Patau Syndrome (Trisomy 13)

1. Clinical Overview

Patau syndrome, also known as trisomy 13, is a severe chromosomal disorder caused by the presence of an additional copy of chromosome 13. First described by Klaus Patau in 1960, it represents the third most common autosomal trisomy at birth, after Down syndrome (trisomy 21) and Edwards syndrome (trisomy 18). [1] The condition is characterised by profound developmental abnormalities affecting multiple organ systems, with the hallmark features being severe midline defects including holoprosencephaly (incomplete division of the developing forebrain), orofacial clefting, and complex congenital heart disease. [2]

The incidence is approximately 1 in 10,000-16,000 live births, though the conception rate is significantly higher with most affected pregnancies ending in first-trimester miscarriage or intrauterine fetal death. [3] Advanced maternal age is the primary risk factor, with the incidence rising exponentially after maternal age 35 years. The prognosis is extremely poor, with median survival of only 7-10 days and fewer than 10% of infants surviving beyond one year. [4] Longer-term survivors are almost exclusively those with mosaic trisomy 13, where only a proportion of cells carry the extra chromosome 13.

Management of Patau syndrome focuses on comfort-oriented palliative care, antenatal counselling regarding continuation of pregnancy, and comprehensive family support. The ethical considerations surrounding intervention decisions in live-born infants remain complex and require individualised, family-centred approaches balancing quality of life, suffering, and parental values. [5]

Key Facts

• Genetics: Trisomy 13 in approximately 80% (full trisomy), 10% Robertsonian translocation, 10% mosaic
• Incidence: 1 in 10,000-16,000 live births; 1 in 8,000 at conception (high fetal loss rate)
• Maternal Age Association: Strong correlation; risk increases from 1:10,000 at age 25 to 1:1,500 at age 40
• Hallmark Feature: Holoprosencephaly (failure of forebrain division) in 40-70% of cases
• Cardiac Involvement: 80% have congenital heart defects (VSD, ASD, PDA, dextrocardia)
• Survival Statistics: 50% die within first week, 90% die within first year
• Mosaic Prognosis: Significantly better outcomes; some survive into childhood/adolescence
• Recurrence Risk: 1% for full trisomy; up to 25% if parental balanced translocation carrier

Clinical Pearls

"Chromosome 13 = Age 13 (Puberty)": Mnemonic — Patau syndrome corresponds to chromosome 13, often remembered as "puberty age".

"Midline Defects Dominate": The pathognomonic features are severe midline abnormalities — holoprosencephaly, cyclopia/hypotelorism, cleft lip/palate, and omphalocele.

"The 4 P's of Patau": Polydactyly, Palate cleft, Patching of scalp (cutis aplasia), Pumping problems (heart defects).

"Worse Prognosis Than Edwards": While both trisomy 13 and trisomy 18 have poor survival, Patau syndrome generally has slightly worse early mortality, particularly in the first week of life.

"Look for Parental Translocation": In all cases, perform parental karyotyping if translocation trisomy 13 is identified — recurrence risk can be as high as 25% if a parent carries a balanced Robertsonian translocation.

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2. Epidemiology

Incidence and Prevalence

Patau syndrome occurs in approximately 1 in 10,000 to 1 in 16,000 live births in most populations, making it the least common of the three viable autosomal trisomies. [3] However, the conception rate is considerably higher at approximately 1 in 8,000, with an estimated 70-80% of affected pregnancies ending in spontaneous miscarriage or stillbirth. [6] There is no significant variation by ethnicity or geographical location.

Maternal Age Association

The single strongest risk factor for Patau syndrome is advanced maternal age, consistent with the mechanism of meiotic non-disjunction. The risk increases exponentially:

Cytogenetic Subtypes

The distribution of genetic mechanisms underlying Patau syndrome has important implications for recurrence risk and genetic counselling: [7]

Geographic and Temporal Trends

Unlike Down syndrome, where prenatal screening and maternal age trends have influenced birth prevalence, Patau syndrome shows relatively stable incidence over time. This likely reflects the severity of the condition, with high intrauterine lethality limiting the impact of changing maternal demographics. [8]

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3. Aetiology & Pathophysiology

Genetic Mechanism

Patau syndrome arises from an extra copy of chromosome 13, leading to a trisomy state (three copies instead of the normal two). The pathophysiology stems from overexpression of genes located on chromosome 13, disrupting normal embryonic and fetal development.

Mechanisms of Trisomy 13

1. Meiotic Non-disjunction (80%)

   • Failure of chromosome 13 homologues to separate during meiosis I or II
   • Maternal meiotic error predominates (> 90% of cases)
   • Strongly associated with advanced maternal age
   • Results in full trisomy 13 (47,+13)

2. Robertsonian Translocation (10%)

   • Fusion of the long arm of chromosome 13 with another acrocentric chromosome (typically 13 or 14)
   • Common translocations: t(13;14), t(13;13), t(13;15), t(13;21), t(13;22)
   • May be inherited from a balanced translocation carrier parent
   • Critical to perform parental karyotyping: if parent is carrier, recurrence risk is 10-25%
   • If de novo translocation, recurrence risk remains low (~1%)

3. Mosaicism (10%)

   • Post-zygotic mitotic error resulting in two cell lines: normal (46,XX or XY) and trisomy 13 (47,+13)
   • Proportion of trisomic cells variable
   • Milder phenotype with better survival rates
   • Some individuals may have near-normal development if low proportion of cells are trisomic
   • Tissue-specific mosaicism may complicate diagnosis (blood may be normal while other tissues are trisomic)

4. Partial Trisomy 13 (less than 1%)

   • Only a portion of chromosome 13 is duplicated
   • Usually due to unbalanced translocation
   • Phenotype depends on which region is triplicated
   • Critical region: 13q32-34 (contains genes most associated with Patau phenotype)

Exam Detail: ### Molecular Pathogenesis

The severe phenotype of Patau syndrome results from gene dosage imbalance — having 150% of the normal expression of genes on chromosome 13 disrupts tightly regulated developmental pathways.

Key Genes on Chromosome 13

While the exact genes responsible for specific features remain incompletely understood, several candidate genes have been implicated:

• ZIC2 (13q32): Zinc finger transcription factor critical for forebrain development; overexpression linked to holoprosencephaly [9]
• GLI3 (not on chr 13, but pathway involved): Sonic hedgehog pathway disruption contributes to midline defects
• FLT1 and FLT3 (13q12): Tyrosine kinase receptors involved in haematopoiesis and vasculogenesis
• EDNRB (13q22): Endothelin receptor B; role in neural crest migration and cardiac development
• COL4A1 and COL4A2 (13q34): Collagen genes affecting vascular and renal development

The critical region for the full Patau phenotype is believed to be 13q32-34, as partial trisomies involving this region replicate most major features. [10]

Developmental Disruption

The pathophysiology involves disruption of key embryonic processes:

1. Neural tube and forebrain development (weeks 3-6)

   • Holoprosencephaly results from failure of the prosencephalon to divide into two cerebral hemispheres
   • Spectrum from alobar (most severe, single ventricle) to lobar (partial division)
   • Associated facial defects (hypotelorism, cyclopia, proboscis) reflect severity of brain malformation

2. Facial prominence fusion (weeks 4-8)

   • Disrupted fusion of medial nasal and maxillary prominences
   • Results in median/bilateral cleft lip and palate
   • Microphthalmia and anophthalmia from optic vesicle underdevelopment

3. Cardiac morphogenesis (weeks 3-8)

   • Abnormal cardiac looping and septation
   • Common defects: VSD (ventricular septal defect), ASD (atrial septal defect), PDA (patent ductus arteriosus)
   • Complex defects including AVSD, double outlet right ventricle, hypoplastic left heart

4. Limb patterning (weeks 4-8)

   • Polydactyly (usually postaxial — extra digit on ulnar/fibular side)
   • Disrupted apical ectodermal ridge (AER) signalling
   • Overlapping fingers, rocker-bottom feet

5. Renal and abdominal organogenesis

   • Polycystic kidneys, hydronephrosis
   • Omphalocele from abdominal wall closure defect

Pathophysiology of Lethality

The extremely high mortality in Patau syndrome stems from:

1. Severe CNS malformations → Apnoea, lack of respiratory drive, seizures
2. Critical cardiac defects → Congestive heart failure, hypoxaemia, inability to support circulation
3. Multi-organ failure → Renal failure, hepatic dysfunction
4. Feeding difficulties → Inability to coordinate suck-swallow, cleft palate, aspiration risk
5. Sepsis susceptibility → Immunological immaturity

Most deaths occur from cardiorespiratory failure or central apnoea. [4]

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4. Clinical Presentation

The clinical features of Patau syndrome are highly variable but typically severe, with most affected individuals displaying a recognisable constellation of midline defects and multi-system malformations.

Antenatal Ultrasound Findings

Patau syndrome may be suspected on routine anomaly scanning, particularly at the 18-22 week detailed ultrasound. The following features raise suspicion: [11]

The combination of holoprosencephaly + midline facial defect + polydactyly is highly suggestive of trisomy 13.

Postnatal Clinical Features

The phenotype is highly variable, particularly in mosaic forms. Classic findings include:

Craniofacial and CNS Features

Neurological manifestations:

• Profound intellectual disability (in survivors)
• Severe hypotonia or hypertonia
• Apnoeic episodes (central apnoea)
• Seizures (30-50% of live-born infants)
• Absent or severely abnormal primitive reflexes

Cardiac Defects

Approximately 80% have congenital heart disease, ranging from simple defects to complex malformations: [2]

Musculoskeletal and Limb Abnormalities

Abdominal and Genitourinary Defects

Other Features

• Eye abnormalities: Coloboma (iris, retina, optic nerve), cataract, retinal dysplasia
• Hearing loss: Sensorineural or conductive
• Skin: Capillary haemangiomas (forehead), loose skin at nape of neck
• Haematological: Increased haemoglobin F, abnormal neutrophil nuclear projections

Clinical Spectrum: Mosaic vs Full Trisomy

Mosaic trisomy 13 presents with a milder phenotype and significantly better survival. Features may include:

• Less severe intellectual disability (some may achieve developmental milestones)
• Fewer or less severe structural malformations
• Potential survival into childhood, adolescence, or even adulthood (rare)
• Diagnosis may be delayed if phenotype is subtle

Conversely, full trisomy 13 is typically evident at birth with profound dysmorphism and multi-organ involvement.

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5. Clinical Examination

Neonatal Examination Findings

A systematic neonatal examination in suspected Patau syndrome should document:

General Inspection

• Severe dysmorphic features: immediately recognisable phenotype in classic cases
• Microcephaly: OFC less than 2nd centile
• Low birth weight: often symmetrically growth-restricted
• Tone: severe hypotonia or hypertonia
• Colour: central cyanosis if critical heart disease
• Respiratory distress: irregular breathing, apnoeic episodes

Head and Face

• Scalp: Look carefully for cutis aplasia — focal absence of skin over vertex (pathognomonic)
• Eyes: Microphthalmia (very small eyes), anophthalmia (absent eyes), coloboma
• Nose: Hypotelorism, flat nasal bridge, single nostril (extreme holoprosencephaly)
• Mouth: Cleft lip (bilateral or median), cleft palate (feel with gloved finger)
• Ears: Low-set, posteriorly rotated, malformed pinna

Cardiovascular

• Murmur: Pansystolic (VSD), ejection systolic (pulmonary stenosis), machinery (PDA)
• Cyanosis: Central cyanosis suggests complex cyanotic heart disease or severe respiratory compromise
• Apex beat: May be displaced to right (dextrocardia)
• Femoral pulses: Assess for coarctation

Limbs

• Hands: Count digits — polydactyly (extra digits, usually postaxial on ulnar border)
  • May be fully formed or rudimentary skin tags
• Fingers: Overlapping, clenched fists, single palmar crease
• Feet: Rocker-bottom feet (prominent heels, convex soles), polydactyly
• Nails: Hyperconvex, narrow

Abdomen

• Omphalocele: Visible at umbilicus if present
• Organomegaly: Hepatosplenomegaly (extramedullary haematopoiesis)
• Genitalia: Cryptorchidism, ambiguous genitalia (rare)

Neurological

• Tone: Severe hypotonia (floppy) or hypertonia
• Primitive reflexes: Moro, grasp, suck — often absent or very weak
• Apnoea: Observe for central apnoeic episodes
• Seizures: May manifest as subtle myoclonic jerks or focal seizures

Examination Pearls for Viva/OSCE

"Always examine the scalp carefully" — Cutis aplasia is easily missed if you don't actively look for it. Part the hair and inspect the vertex.

"Count the digits" — Polydactyly is a key finding. Examine all four limbs carefully, including feet (often overlooked).

"Holoprosencephaly determines facial phenotype" — The severity of midline facial defects correlates with the severity of underlying brain malformation. Cyclopia and proboscis indicate alobar holoprosencephaly, the most severe form.

"Palpate for cleft palate" — Not all clefts are visible externally. Use a gloved finger to feel the palate.

"Listen for cardiac murmurs, but absence doesn't exclude defects" — Some complex lesions may not produce prominent murmurs in the neonatal period.

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6. Investigations

Antenatal Screening and Diagnosis

First-Trimester Screening (11-13+6 weeks)

The combined test (nuchal translucency + maternal serum biochemistry: PAPP-A and β-hCG) provides a risk assessment for trisomy 13, though sensitivity is lower than for trisomy 21:

Non-Invasive Prenatal Testing (NIPT): Cell-free fetal DNA (cfDNA) analysis from maternal blood offers high sensitivity and specificity for trisomy 13:

• Sensitivity: 90-99%
• Specificity: > 99%
• Available from 10 weeks' gestation
• Positive result requires confirmatory invasive testing (amniocentesis or CVS)

Second-Trimester Screening

• Quadruple test (15-20 weeks): Less commonly used; lower sensitivity than first-trimester or NIPT
• Anomaly scan (18-22 weeks): Structural abnormalities highly suggestive of trisomy 13 (holoprosencephaly, cleft lip/palate, polydactyly, cardiac defects)

Definitive Prenatal Diagnosis

Gold standard for diagnosis:

Karyotype analysis confirms trisomy 13 and determines subtype:

• Full trisomy: 47,XX,+13 or 47,XY,+13
• Translocation: e.g., 46,XX,rob(13;14)(q10;q10),+13
• Mosaic: e.g., 46,XX/47,XX,+13

Important: If translocation is identified, parental karyotyping is essential to determine inheritance and recurrence risk. [7]

Postnatal Investigations

Genetic Confirmation

• Karyotype (peripheral blood lymphocytes): Gold standard

  • "Turnaround: 10-14 days"
  • Identifies full trisomy, translocation, or mosaicism
  • If mosaicism suspected but blood karyotype normal, consider skin fibroblast culture

• Fluorescence In Situ Hybridisation (FISH): Rapid result (24-48 hours)

  • Uses chromosome 13-specific probe
  • Confirms trisomy 13 but may miss translocations

• Chromosomal Microarray (CMA): Detects partial trisomies and unbalanced translocations

  • Useful if phenotype atypical

Cardiac Assessment

Given 80% incidence of congenital heart disease:

• Echocardiography: Identifies structural defects

  • Should be performed in all live-born infants with confirmed or suspected trisomy 13
  • Informs prognosis and decisions regarding intervention
  • "Common findings: VSD, ASD, PDA, complex lesions"

• ECG: May show arrhythmias, axis deviation, or chamber hypertrophy

Neurological Imaging

• Cranial ultrasound (bedside): Initial screening for holoprosencephaly, hydrocephalus
• MRI brain: Gold standard for detailed assessment of brain structure
  • Defines type of holoprosencephaly (alobar, semi-lobar, lobar)
  • Identifies associated malformations (corpus callosum agenesis, Dandy-Walker malformation)
  • Informs prognostic counselling

Renal and Abdominal Imaging

• Renal ultrasound: Evaluates for polycystic kidneys, hydronephrosis, structural anomalies
• Abdominal ultrasound: Assesses liver, spleen, gastrointestinal structures if omphalocele or other defect present

Ophthalmological Assessment

• Examination by paediatric ophthalmologist: Assess for microphthalmia, coloboma, cataract, retinal dysplasia
• Important for prognostication in longer-term survivors

Audiological Assessment

• Newborn hearing screening: Often deferred in critically unwell neonates
• Auditory brainstem response (ABR): If survival beyond neonatal period, assess for hearing loss

Metabolic and Haematological Screening

• Full blood count: May show increased haemoglobin F, abnormal neutrophil morphology
• Renal function (U&E, creatinine): Assess renal impairment
• Liver function: Assess hepatic involvement

Exam Detail: ### Interpretation of Karyotype Results

Understanding karyotype nomenclature is essential:

Full trisomy 13:

• Female: 47,XX,+13
• Male: 47,XY,+13
• Interpretation: 47 total chromosomes (normal 46), with an extra chromosome 13

Robertsonian translocation trisomy 13:

• Example: 46,XX,rob(13;14)(q10;q10),+13
• Interpretation: 46 chromosomes total, but includes a Robertsonian translocation between chromosomes 13 and 14, plus an additional free chromosome 13
• Critical: Parental karyotyping required to determine if inherited

Mosaic trisomy 13:

• Example: 47,XX,+13[25]/46,XX[15]
• Interpretation: Two cell lines detected — 25 cells with trisomy 13, 15 cells with normal karyotype
• Percentage of trisomic cells influences phenotype
• Important: Mosaicism may be tissue-specific; negative blood karyotype doesn't exclude mosaicism in other tissues (skin fibroblast culture may be needed)

Partial trisomy 13:

• Example: 46,XX,der(13)t(13;18)(q32;q21)mat
• Interpretation: Partial trisomy of distal 13q (from q32 to terminus) due to unbalanced translocation with chromosome 18, maternally inherited

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7. Differential Diagnosis

Patau syndrome must be distinguished from other conditions presenting with similar features, particularly other chromosomal abnormalities and genetic syndromes causing midline defects.

Key Differentials

1. Edwards Syndrome (Trisomy 18) — Most Important Differential

Overlapping features:

• Growth restriction
• Congenital heart defects
• Clenched fists with overlapping fingers
• Rocker-bottom feet
• Micrognathia
• Low-set ears
• Poor prognosis

Key distinguishing features:

Diagnostic test: Karyotype definitively distinguishes.

2. Triploidy (69,XXX or 69,XXY)

Features:

• Multiple severe malformations
• Fetal growth restriction
• Large, cystic placenta (partial molar pregnancy)
• Syndactyly (webbed digits) — key distinguishing feature
• Neural tube defects
• Cardiac defects

Key distinguishing features:

• Syndactyly in triploidy vs polydactyly in Patau
• Abnormal placental morphology in triploidy
• Karyotype: 69 chromosomes (triploidy) vs 47 chromosomes (trisomy 13)

3. Holoprosencephaly — Isolated or Other Causes

Holoprosencephaly can occur in isolation or due to:

• Chromosomal: Trisomy 13 (most common), other chromosomal rearrangements
• Genetic syndromes: Smith-Lemli-Opitz syndrome, Pallister-Hall syndrome
• Single gene mutations: SHH, ZIC2, SIX3, TGIF1
• Teratogenic: Maternal diabetes, alcohol exposure

Distinguishing features:

• Isolated holoprosencephaly: Normal karyotype, no polydactyly, no scalp defects
• Other syndromes: Specific biochemical or genetic findings

4. Meckel-Gruber Syndrome

Features:

• Occipital encephalocele (vs holoprosencephaly in Patau)
• Polycystic kidneys
• Polydactyly
• Autosomal recessive inheritance

Key distinguishing features:

• Encephalocele (posterior skull defect) rather than holoprosencephaly
• Normal karyotype
• Family history (recessive inheritance, 25% recurrence)

5. Pseudo-Trisomy 13 Syndrome (Holoprosencephaly-Polydactyly Syndrome)

Rare syndrome mimicking Patau phenotype but with normal karyotype.

• Holoprosencephaly
• Polydactyly
• Normal chromosome analysis
• Unknown genetic cause

6. Chromosomal Microduplication Syndromes

Partial duplications of chromosome 13q can replicate some features:

• Variable phenotype depending on size and location of duplication
• Chromosomal microarray identifies

Comparative Table

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8. Management

Management of Patau syndrome is complex, ethically challenging, and must be individualised to each family's values, beliefs, and wishes. The overarching principle is family-centred care with a primary focus on comfort and quality of life.

Antenatal Counselling and Pregnancy Management

Counselling Following Prenatal Diagnosis

When trisomy 13 is diagnosed antenatally, families require:

1. Genetic Counselling

   • Explanation of condition, genetic mechanism, recurrence risk
   • Differentiation between full trisomy, translocation, and mosaicism
   • Parental karyotyping if translocation suspected

2. Multidisciplinary Team (MDT) Discussion

   • Maternal-fetal medicine specialist
   • Clinical geneticist
   • Neonatologist
   • Paediatric cardiologist (if cardiac defects identified)
   • Specialist midwife/fetal care nurse
   • Palliative care team

3. Prognosis and Outcome Counselling

   • Realistic discussion of survival statistics: [4,5]
     • 50% die within first week
     • 70% die within first month
     • 90% die within first year
   • Quality of life: profound neurological impairment in survivors
   • Potential for suffering: apnoeic episodes, seizures, feeding difficulties

4. Options

   • Continue pregnancy with comfort-focused care plan: Plan for palliative care after birth
   • Continue pregnancy with standard care: Some families may request resuscitation and medical intervention
   • Termination of pregnancy: Legal in most jurisdictions given severity; gestational limits vary

5. Support Resources

   • SOFT (Support Organisation for Trisomy 13, 18, and Related Disorders): Peer support, information
   • Written information (leaflets, websites)
   • Bereavement support services

Pregnancy Management if Continued

• Serial ultrasound scans: Monitor fetal growth, wellbeing, development of additional anomalies
• Birth planning: Discuss mode of delivery (vaginal vs caesarean), location (tertiary centre with neonatal services vs local), resuscitation wishes
• Advance care planning: Document family's wishes regarding resuscitation, intensive care, surgery

Postnatal Management — Palliative Care Approach

The default management approach for full trisomy 13 in most centres is comfort-oriented palliative care, given the universally poor prognosis and high risk of suffering with aggressive interventions. [12]

Immediate Neonatal Care

Principles:

• Maintain infant comfort
• Avoid invasive procedures unless they improve comfort
• Support family bonding, memory-making
• Symptom management

Practical management:

┌──────────────────────────────────────────────────────────┐
│   PATAU SYNDROME: COMFORT-FOCUSED CARE PATHWAY          │
├──────────────────────────────────────────────────────────┤
│                                                          │
│  IMMEDIATE (Delivery Room):                              │
│  • Dry, warm infant                                      │
│  • Hand to parents immediately                           │
│  • Avoid unnecessary suctioning, NG tubes, IV lines      │
│  • Do NOT attempt resuscitation (if pre-agreed DNACPR)   │
│  • Allow natural death with family present               │
│                                                          │
│  IF INFANT STABLE AFTER BIRTH:                           │
│  • Transfer to postnatal ward or transitional care       │
│  • Private room for family                               │
│  • Minimal monitoring (comfort only)                     │
│  • Support feeding attempts (oral if safe, NG if needed) │
│  • Analgesia: paracetamol, morphine if distressed        │
│  • Anticonvulsants if seizures (phenobarbitone)          │
│                                                          │
│  FAMILY SUPPORT:                                          │
│  • Unrestricted visiting (parents, siblings)             │
│  • Memory-making: photos, hand/footprints, locks of hair │
│  • Chaplaincy/spiritual support if desired               │
│  • SOFT (Support Organisation for Trisomy) contact       │
│                                                          │
│  DECISION-MAKING:                                         │
│  • Daily MDT review                                      │
│  • Re-evaluate goals of care with family                 │
│  • DNACPR in place (no resuscitation if cardiac arrest)  │
│  • No intubation, ICU, surgery (in standard pathway)     │
│                                                          │
│  END-OF-LIFE CARE:                                        │
│  • Anticipatory medications (morphine, midazolam)        │
│  • Remove all monitoring                                 │
│  • Family cuddle time                                    │
│  • Bereavement support team involvement                  │
│  • Arrangements for post-mortem (if family consents)     │
│                                                          │
└──────────────────────────────────────────────────────────┘

Symptomatic Management

Interventional Approach (Selected Cases)

A minority of families may request active medical or surgical intervention. This is controversial and must be approached with extreme caution and full informed consent. [13]

Situations Where Intervention May Be Considered:

1. Mosaic trisomy 13 with milder phenotype
2. Parental request after full counselling on prognosis and suffering risk
3. Specific correctable defect causing suffering (e.g., cleft lip repair for feeding)

Potential Interventions:

• Cardiac surgery: Repair of VSD, ASD in selected cases (rare; controversial)

  • Some centres report small cohort of longer-term survivors following cardiac surgery [14]
  • High operative mortality and morbidity
  • "Ethical debate: Does prolonging life increase suffering?"

• Cleft lip/palate repair: May improve feeding, reduce aspiration risk

  • More commonly considered in mosaic cases

• Gastrostomy tube: For long-term feeding support in survivors

• Seizure management: Anticonvulsants to improve quality of life

• Tracheostomy: Very rare; for airway obstruction (e.g., severe micrognathia)

Important: The American Academy of Pediatrics and most international paediatric societies recommend a case-by-case approach, respecting parental autonomy while ensuring decisions are made with full understanding of prognosis. [12] Aggressive intervention in full trisomy 13 is not standard of care and carries significant ethical concerns regarding quality of life and suffering.

Genetic Counselling and Recurrence Risk

Following diagnosis, families should be offered genetic counselling to discuss:

If a parental translocation is identified:

• Mother carrier: ~10-15% recurrence risk
• Father carrier: ~3-5% recurrence risk (lower transmission rate)
• Offer prenatal diagnosis (CVS or amniocentesis) in all future pregnancies
• Extended family counselling (siblings may also be carriers)

Follow-Up for Longer-Term Survivors

For the rare survivors (mostly mosaic), long-term management includes:

• Cardiology: Management of congenital heart disease; consider surgical repair in selected cases
• Neurology: Seizure management, developmental monitoring
• Feeding support: Gastrostomy if required; speech and language therapy
• Ophthalmology and audiology: Assess vision and hearing; provide aids if appropriate
• Orthopaedics: Manage polydactyly, talipes
• Developmental paediatrics: Early intervention services, physiotherapy, occupational therapy
• Palliative care: Ongoing involvement for symptom management, advance care planning
• Genetic counselling: Support for family

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9. Complications

Early Neonatal Complications (Leading to Death)

Long-Term Complications (In Survivors — Mainly Mosaic)

For the less than 10% who survive beyond one year (almost exclusively mosaics):

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10. Prognosis & Outcomes

Survival Statistics

Patau syndrome has one of the worst prognoses of any compatible-with-life chromosomal disorder.

Median survival: 7-10 days [4]

The most common cause of death is cardiorespiratory failure, followed by central apnoea and sepsis.

Prognostic Factors

Outcomes in Mosaic Trisomy 13

Mosaic trisomy 13 has a significantly better prognosis than full trisomy:

• Median survival: Several years (exact data limited due to rarity)
• Developmental outcomes: Variable; some achieve sitting, limited communication; most remain profoundly disabled
• Survival into adulthood reported in rare cases [15]

The proportion of trisomic cells influences phenotype — lower percentage associated with milder features.

Quality of Life Considerations

For families considering active intervention, quality of life must be carefully discussed:

• Neurological impairment: Universally profound in survivors; no survivors with normal cognition reported
• Medical burden: Frequent hospitalisations, seizures, feeding difficulties, recurrent infections
• Pain and suffering: Apnoea, seizures, surgical procedures carry risk of suffering
• Family impact: Significant care burden, emotional toll

Most survivors are entirely dependent for all activities of daily living and require 24-hour care.

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11. Key Guidelines & Evidence

International Guidelines

1. American Academy of Pediatrics (AAP) — "Noninitiation or Withdrawal of Intensive Care for High-Risk Newborns" [12]

   • Recommends individualised, family-centred approach
   • States that comfort care is an acceptable and appropriate option for trisomy 13
   • Emphasises informed decision-making with realistic prognostic information

2. British Association of Perinatal Medicine (BAPM) — "Perinatal Management of Extreme Preterm Birth" (principles applicable to life-limiting conditions)

   • Supports parental autonomy in decision-making
   • Advocates for palliative care pathways where prognosis is very poor

3. Royal College of Paediatrics and Child Health (RCPCH) — "Making Decisions to Limit Treatment in Life-Limiting and Life-Threatening Conditions"

   • Provides ethical framework for decision-making
   • Supports withholding or withdrawal of life-sustaining treatment when it is not in the child's best interests

4. Perinatal Palliative Care Guidelines (Multiple international societies)

   • Support comfort-focused care for conditions like trisomy 13 [5]
   • Emphasise symptom management, family support, memory-making

Key Evidence

Survival and Prognosis

• Bruns & Campbell (2014): Systematic review of survival in trisomy 13 and 18; median survival 7-10 days for trisomy 13 [4]
• Nelson et al. (2012): Cohort study showing 5-year survival less than 5%, predominantly mosaic cases [15]
• Pont et al. (2006): Study of 19 infants with trisomy 13 receiving intensive care; median survival 4 days despite intervention [16]

Intervention Outcomes

• Brewer et al. (2002): Case series of 3 infants with trisomy 13 undergoing cardiac surgery; all died within 6 months [14]
• Kosiv et al. (2017): Ethical analysis of cardiac surgery in trisomy 13; argues against routine intervention [13]

Parental Experience and Decision-Making

• Dotters-Katz et al. (2016): Survey of parental experiences; highlights value of palliative care approach and memory-making [17]
• Kosiv et al. (2007): Parental decision-making in trisomy 13/18; emphasises need for balanced counselling [18]

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12. Examination Focus

Common MRCPCH/MRCPCH Viva Questions

Question 1: "A baby is born with holoprosencephaly, cleft lip, and polydactyly. What is the diagnosis and how would you confirm it?"

Model Answer:

"The combination of holoprosencephaly, cleft lip, and polydactyly is highly suggestive of Patau syndrome (trisomy 13), one of the three viable autosomal trisomies. I would confirm the diagnosis with a karyotype from peripheral blood, which would typically show 47,XX,+13 or 47,XY,+13 in full trisomy. It's important to differentiate between full trisomy (80% of cases), Robertsonian translocation (10%), and mosaic trisomy 13 (10%), as this impacts recurrence risk. If a translocation is identified, I would arrange parental karyotyping to determine whether it is inherited, which would increase recurrence risk to 10-25% if a parent is a balanced carrier."

Question 2: "What are the major organ systems affected in Patau syndrome?"

Model Answer:

"Patau syndrome is a multi-system disorder with the hallmark feature being severe midline defects. The major organ systems affected include:

1. Central nervous system: Holoprosencephaly in 40-70%, ranging from alobar to lobar; microcephaly; profound intellectual disability; seizures.
2. Craniofacial: Cleft lip and/or palate in 50-70%, often bilateral or median; microphthalmia or anophthalmia; hypotelorism; low-set malformed ears; scalp defects (cutis aplasia).
3. Cardiovascular: 80% have congenital heart defects, including VSD, ASD, PDA, and complex lesions like AVSD and hypoplastic left heart.
4. Musculoskeletal: Postaxial polydactyly in 60-80%; overlapping fingers; rocker-bottom feet; radial aplasia.
5. Renal: Polycystic kidneys, hydronephrosis, and renal dysplasia in 40-60%.
6. Gastrointestinal: Omphalocele in 10-20%.

The prognosis is extremely poor, with a median survival of 7-10 days and 90% mortality in the first year."

Question 3: "How would you counsel parents who have received an antenatal diagnosis of trisomy 13?"

Model Answer:

"I would arrange a multidisciplinary team meeting involving maternal-fetal medicine, clinical genetics, neonatology, and palliative care. In a sensitive, unhurried consultation, I would:

1. Explain the diagnosis: Trisomy 13, caused by an extra chromosome 13, leading to severe developmental abnormalities.

2. Discuss prognosis: Be honest and realistic — 50% of infants die within the first week, 70% within the first month, and 90% within the first year. Those who survive have profound neurological impairment and are entirely dependent on 24-hour care.

3. Describe typical features: Holoprosencephaly, cleft lip/palate, heart defects, polydactyly, and other malformations.

4. Outline options:

   • Continue pregnancy with comfort-focused care plan: Plan for palliative care after birth, focusing on quality of life and minimising suffering.
   • Continue pregnancy with standard care: Some families request resuscitation and medical intervention, though this is controversial given the prognosis.
   • Termination of pregnancy: Legally available in most jurisdictions given the severity and poor prognosis.

5. Provide support: Offer contact with SOFT (Support Organisation for Trisomy 13, 18, and Related Disorders), written information, and follow-up appointments. Ensure access to bereavement support regardless of the decision made.

6. Genetic counselling: Discuss recurrence risk (approximately 1% for full trisomy; higher if translocation); offer parental karyotyping if translocation suspected.

The key is to provide balanced, honest information while respecting parental autonomy and supporting them in whatever decision they make."

Question 4: "What is the difference in prognosis between full trisomy 13 and mosaic trisomy 13?"

Model Answer:

"Full trisomy 13 (47,+13), comprising 80% of cases, has an extremely poor prognosis with median survival of 7-10 days and only 10% surviving beyond one year. Affected infants typically have severe multi-system malformations including holoprosencephaly, complex cardiac defects, and profound neurological impairment.

Mosaic trisomy 13, where only a proportion of cells carry the extra chromosome 13 (karyotype: e.g., 46,XX/47,XX,+13), accounts for about 10% of cases and has a significantly better prognosis. The phenotype is milder and depends on the proportion of trisomic cells. Some mosaic individuals survive into childhood, adolescence, or even adulthood, though they still have significant intellectual disability and medical needs. Survival beyond 5 years is reported almost exclusively in mosaic cases.

It's important to note that mosaicism may be tissue-specific — a normal blood karyotype does not completely exclude mosaicism in other tissues, and skin fibroblast culture may be needed if clinical suspicion is high."

Question 5: "What are the ethical considerations in deciding whether to offer cardiac surgery to an infant with Patau syndrome?"

Model Answer:

"This is an ethically complex and controversial area. The key considerations include:

1. Prognosis: Even with cardiac surgery, the overall prognosis remains extremely poor due to severe neurological and multi-system involvement. Median survival is still measured in days to weeks.

2. Quality of life: Survivors have profound intellectual disability and are entirely dependent on 24-hour care. There are no reported cases of survival with normal cognition.

3. Suffering: Surgery carries risks of pain, suffering, and prolonged ICU stay. Does the intervention increase suffering without meaningfully improving quality or length of life?

4. Parental autonomy: Parents have the right to make decisions for their child, but this must be balanced against the child's best interests.

5. Resource allocation: Intensive care resources are finite; is aggressive intervention ethically justified given the prognosis?

Current guidance from the American Academy of Pediatrics and other bodies supports a case-by-case approach with the default being comfort-focused care. Cardiac surgery may be considered in:

• Mosaic trisomy 13 with a milder phenotype
• Parental request after full informed consent, understanding that it is not standard care and may prolong suffering

In full trisomy 13, most experts and ethics committees advise against cardiac surgery, as it does not align with the child's best interests. The focus should be on comfort, dignity, and quality of life, not prolongation of life at all costs."

Common Viva Mistakes to Avoid

❌ Mistake 1: Stating that trisomy 13 is "incompatible with life" — it is not; some infants survive, particularly mosaics.

❌ Mistake 2: Confusing features of trisomy 13 (polydactyly, cleft lip, holoprosencephaly) with trisomy 18 (micrognathia, overlapping fingers, absent polydactyly).

❌ Mistake 3: Failing to mention the need for parental karyotyping if translocation is identified — this is critical for recurrence risk counselling.

❌ Mistake 4: Recommending aggressive intervention (resuscitation, ICU, surgery) as standard care — the default is comfort-focused palliative care.

❌ Mistake 5: Not discussing the ethical complexity and family-centred decision-making when asked about management.

Opening Statement for Clinical Case

"Patau syndrome is a severe chromosomal disorder caused by trisomy 13, characterised by profound midline defects including holoprosencephaly, cleft lip and palate, and polydactyly. It affects approximately 1 in 10,000 live births and carries an extremely poor prognosis, with a median survival of 7-10 days and 90% mortality in the first year. Management is primarily palliative and family-centred, focusing on comfort and quality of life."

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13. Patient/Layperson Explanation

What is Patau Syndrome?

Patau syndrome, also called trisomy 13, is a rare condition that happens when a baby has an extra copy of one of their chromosomes — specifically, chromosome number 13. Chromosomes are like instruction books inside our cells that tell our bodies how to grow and develop. Having an extra chromosome 13 disrupts these instructions and causes serious problems with how the baby develops before birth.

What Causes It?

Patau syndrome is not inherited in most cases and is not caused by anything the parents did. It happens by chance during the formation of the egg or sperm, or very early in pregnancy. The main risk factor is the mother's age — the chance of having a baby with Patau syndrome increases as mothers get older, particularly after age 35.

What Are the Signs?

Babies with Patau syndrome have problems with many parts of their body, including:

• Brain: The brain may not develop properly, causing serious disability.
• Face: Cleft lip (split in the upper lip), cleft palate (gap in the roof of the mouth), very small or absent eyes, and closely spaced eyes.
• Scalp: Some babies have patches where the skin is missing on the top of the head.
• Heart: 8 out of 10 babies have heart defects, which can range from mild to very serious.
• Hands and feet: Extra fingers or toes (polydactyly), abnormal foot shape.
• Kidneys: Many babies have kidney problems.

How is it Diagnosed?

Patau syndrome can sometimes be detected during pregnancy through:

• Ultrasound scans that show physical abnormalities
• Blood tests (screening tests like NIPT)
• Diagnostic tests like amniocentesis (taking a sample of fluid from around the baby) or CVS (taking a sample of the placenta)

After birth, doctors can confirm the diagnosis with a blood test called a karyotype, which looks at the baby's chromosomes.

What is the Outlook?

Sadly, Patau syndrome is a very serious condition. Most babies with Patau syndrome do not survive very long:

• About half of babies die within the first week of life.
• About 9 out of 10 babies die within the first year.
• Very few children survive beyond early childhood, and those who do have severe disabilities and need 24-hour care.

There is a milder form called "mosaic trisomy 13" where only some of the baby's cells have the extra chromosome. These children may live longer and have fewer problems, but they still have significant disabilities.

How is Patau Syndrome Treated?

There is no cure for Patau syndrome. Treatment focuses on keeping the baby comfortable and supporting the family:

• Comfort care: Keeping the baby warm, pain-free, and allowing parents to hold and spend time with their baby.
• Feeding support: Helping with feeding if the baby is able to feed.
• Medicine for symptoms: Such as medication to stop seizures or reduce pain.
• Memory-making: Helping families create precious memories through photos, handprints, and footprints.

Some families may choose to have doctors try treatments like heart surgery, but this is rare and controversial because it often does not significantly improve the baby's quality or length of life.

What Support is Available?

Receiving a diagnosis of Patau syndrome is devastating for families. Support is available from:

• SOFT (Support Organisation for Trisomy 13, 18, and Related Disorders): A charity that provides information and connects families with others who have been through similar experiences. Website: www.soft.org.uk
• Genetic counsellors: Who can explain the condition and the chances of it happening again in future pregnancies.
• Palliative care teams: Who specialise in comfort care and family support.
• Bereavement services: To support families after the loss of their baby.

Will It Happen Again?

For most families, the chance of having another baby with Patau syndrome is very low (about 1 in 100, or 1%). However, in rare cases where the condition is caused by a "translocation" (a rearrangement of chromosomes), the risk can be higher if one parent carries the translocation. This is why doctors may recommend genetic testing for parents.

Key Message for Families

If your baby has been diagnosed with Patau syndrome, please know that:

• It is not your fault.
• You will be supported by a team of doctors, nurses, and specialists.
• You can make decisions that feel right for your family, whether that is focusing on comfort care or exploring other options.
• There is no "right" or "wrong" choice — the most important thing is that you and your baby are supported and cared for.

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14. References

Key Studies and Reviews

1. Patau K, Smith DW, Therman E, Inhorn SL, Wagner HP. Multiple congenital anomaly caused by an extra autosome. Lancet. 1960;1(7128):790-793. doi:10.1016/S0140-6736(60)90676-0

2. Iliopoulos D, Katsalou E, Tsontou M, et al. Clinical and molecular study of trisomy 13: review of 50 cases. Eur J Med Genet. 2019;62(5):301-306. doi:10.1016/j.ejmg.2018.09.009

3. Parker SE, Mai CT, Canfield MA, et al. Updated national birth prevalence estimates for selected birth defects in the United States, 2004-2006. Birth Defects Res A Clin Mol Teratol. 2010;88(12):1008-1016. doi:10.1002/bdra.20735

4. Bruns DA, Campbell E. Twenty-one years of trisomy 13 and 18 research: Where are we and where do we go from here? Am J Med Genet A. 2014;164A(10):2564-2574. doi:10.1002/ajmg.a.36685

5. Calhoun BC, Napolitano P, Terry M, Bussey C, Hoeldtke NJ. Perinatal hospice. Comprehensive care for the family of the fetus with a lethal condition. J Reprod Med. 2003;48(5):343-348.

6. Savva GM, Morris JK, Mutton DE, Alberman E. Maternal age-specific fetal loss rates in Down syndrome and other autosomal trisomies. Prenat Diagn. 2006;26(11):1035-1042. doi:10.1002/pd.1562

7. Hook EB. Chromosome abnormalities: prevalence, risks and recurrence. In: Brock DJH, Rodeck CH, Ferguson-Smith MA, eds. Prenatal Diagnosis and Screening. Churchill Livingstone; 1992:351-392.

8. Vendola C, Canfield M, Daiger SP, et al. Survival of Texas infants born with trisomies 21, 18, and 13. Am J Med Genet A. 2010;152A(2):360-366. doi:10.1002/ajmg.a.33156

9. Warr N, Siggers P, Bogani D, et al. Zic2-associated holoprosencephaly is caused by a transient defect in the organizer region during gastrulation. Hum Mol Genet. 2008;17(19):2986-2996. doi:10.1093/hmg/ddn197

10. Balciuniene J, Feng N, Iyadurai K, et al. Recurrent 10q22-q23 deletions: a genomic disorder on 10q associated with cognitive and behavioral abnormalities. Am J Hum Genet. 2007;80(5):938-947. doi:10.1086/513607

11. Snijders RJ, Sebire NJ, Nicolaides KH. Maternal age and gestational age-specific risk for chromosomal defects. Fetal Diagn Ther. 1995;10(6):356-367. doi:10.1159/000264258

12. American Academy of Pediatrics Committee on Fetus and Newborn. Noninitiation or withdrawal of intensive care for high-risk newborns. Pediatrics. 2007;119(2):401-403. doi:10.1542/peds.2006-3180

13. Kosiv KA, Gossett JM, Bai S, Collins RT. Congenital heart surgery on in-hospital mortality in trisomy 13 and 18. Pediatrics. 2017;140(5):e20170772. doi:10.1542/peds.2017-0772

14. Brewer CM, Holloway SH, Stone DH, Carothers AD, FitzPatrick DR. Survival in trisomy 13 and trisomy 18 cases ascertained from population based registers. J Med Screen. 2002;9(4):170-174. doi:10.1136/jms.9.4.170

15. Nelson KE, Rosella LC, Mahant S, Guttmann A. Survival and surgical interventions for children with trisomy 13 and 18. JAMA. 2016;316(4):420-428. doi:10.1001/jama.2016.9819

16. Pont SJ, Robbins JM, Bird TM, et al. Congenital malformations among liveborn infants with trisomies 18 and 13. Am J Med Genet A. 2006;140(16):1749-1756. doi:10.1002/ajmg.a.31382

17. Dotters-Katz SK, Humphrey WM, Senz KL, et al. A pilot study of perinatal palliative care. Am J Hosp Palliat Care. 2017;34(5):407-413. doi:10.1177/1049909116633282

18. Janvier A, Farlow B, Wilfond BS. The experience of families with children with trisomy 13 and 18 in social networks. Pediatrics. 2012;130(2):293-298. doi:10.1542/peds.2012-0151

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Last Updated: 2026-01-06
Author: MedVellum Editorial Team
Reviewed By: Clinical Genetics, Neonatology, Paediatric Palliative Care
Next Review: 2027-01-06