Neurofibromatosis Type 1 (NF1)

1. Clinical Overview

Summary

Neurofibromatosis Type 1 (NF1), historically known as Von Recklinghausen disease, is the most common neurocutaneous syndrome (phakomatosis) and one of the most prevalent single-gene disorders affecting the nervous system. It affects approximately 1 in 2,500 to 3,000 live births worldwide, with no ethnic or geographic predilection. [1,2]

NF1 is an autosomal dominant disorder caused by loss-of-function mutations in the NF1 tumour suppressor gene located on chromosome 17q11.2. This gene encodes neurofibromin, a large cytoplasmic protein of 2,818 amino acids that functions primarily as a GTPase-Activating Protein (GAP) for the RAS proto-oncogene family. Loss of neurofibromin results in constitutive activation of the RAS-MAPK signalling cascade, driving uncontrolled cellular proliferation, particularly in neural crest-derived tissues. [3,4]

The disorder demonstrates complete penetrance by age 8-10 years but exhibits remarkably variable expressivity - even within the same family carrying identical mutations, phenotypic severity can range from a few café-au-lait macules to severe disfiguring plexiform neurofibromas and life-threatening malignancies. Approximately 50% of cases arise from de novo mutations, with a notable paternal age effect. [1,5]

Clinical diagnosis follows the revised International Consensus diagnostic criteria (2021), which updated the original 1988 NIH criteria to incorporate genetic testing and distinguish NF1 from the phenotypically overlapping Legius syndrome. The seven diagnostic features include café-au-lait macules, neurofibromas, axillary/inguinal freckling, optic pathway glioma, Lisch nodules, distinctive osseous lesions, and a first-degree relative with NF1. The 2021 revision added bilateral choroidal abnormalities and a heterozygous pathogenic NF1 variant as independent diagnostic criteria. [6]

While most individuals with NF1 have normal or near-normal life expectancy, the condition carries significant morbidity from tumour burden, skeletal abnormalities, cognitive impairment, and cardiovascular disease. The lifetime risk of malignant peripheral nerve sheath tumour (MPNST) is 8-13%, representing the most feared complication. Recent therapeutic advances, particularly the FDA approval of the MEK inhibitor selumetinib for inoperable plexiform neurofibromas in 2020, have transformed the management landscape. [7,8]

Key Facts

Clinical Pearls

"Coast of California": The borders of café-au-lait macules in NF1 are characteristically smooth and regular, likened to the smooth coastline of California. This distinguishes them from McCune-Albright syndrome where macules have irregular, "jagged" borders (Coast of Maine).

"Crowe's Sign": Axillary or inguinal freckling (multiple small pigmented macules in non-sun-exposed skin folds) is pathognomonic for NF1 when present. It typically appears by age 5-7 years and is the most specific sign in early childhood.

"The Ugly Duckling": Among hundreds of soft, mobile cutaneous neurofibromas, any lesion that is hard, fixed, rapidly growing, or painful demands urgent investigation for malignant transformation to MPNST. Pain and rapid growth are the most sensitive warning signs.

"UBOs are not tumours": Unidentified Bright Objects (UBOs) or Focal Areas of Signal Intensity (FASI) on T2-weighted MRI are seen in 70-80% of children with NF1. These represent areas of vacuolar change/myelin dysplasia, NOT neoplasms. They typically regress by adulthood and require no treatment.

"Check the blood pressure": Hypertension in NF1 has three main causes: essential hypertension (vasculopathy), renal artery stenosis (fibromuscular dysplasia pattern), or phaeochromocytoma. All patients require regular BP monitoring.

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2. Epidemiology

Incidence and Prevalence

NF1 is among the most common autosomal dominant genetic disorders worldwide. Epidemiological data demonstrate:

The higher birth incidence compared to population prevalence reflects reduced survival and reproductive fitness in severely affected individuals. The NF1 gene has one of the highest spontaneous mutation rates of any human gene due to its large size (approximately 350 kb of genomic DNA). [3]

Demographics

• Sex Distribution: Equal male:female ratio (1:1)
• Ethnic Distribution: Pan-ethnic with no documented predilection
• Geographic Distribution: Worldwide distribution
• Paternal Age Effect: De novo mutations show correlation with advanced paternal age, consistent with accumulation of errors during spermatogenesis [5]

Genetic Epidemiology

Penetrance and Expressivity

The penetrance of NF1 is virtually 100% by age 8-10 years when using comprehensive clinical evaluation. However, the expressivity is highly variable:

• Affected individuals within the same family carrying identical NF1 mutations can exhibit vastly different phenotypes
• Phenotypic variability is influenced by modifying genes, stochastic events (second-hit mutations), and epigenetic factors
• No reliable genotype-phenotype correlations exist for most mutations, with notable exceptions:
  • "Whole-gene deletions (~1.4 Mb): More severe phenotype, dysmorphic features, lower IQ, earlier/more numerous neurofibromas [9]"
  • "Missense mutation p.Met1149: Mild phenotype with pigmentary features only [6]"
  • "c.2970-2972del (p.Met992del): NF1-Noonan syndrome phenotype [6]"

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3. Aetiology and Genetics

The NF1 Gene

The NF1 gene was identified in 1990 through positional cloning and represents one of the largest human genes:

The gene contains three embedded genes within intron 27 (OMGP, EVI2A, EVI2B) transcribed from the opposite strand, a highly unusual genomic arrangement. [3]

Mutation Spectrum

Over 3,000 different pathogenic NF1 variants have been identified:

Approximately 95% of mutations are predicted to result in loss of function (null alleles), supporting the tumour suppressor model. The remaining 5% are in-frame deletions/insertions or missense variants affecting critical functional domains. [4]

Neurofibromin: Structure and Function

Neurofibromin is a large cytoplasmic protein with multiple functional domains:

Critical Functional Domain:

• GTPase-Activating Protein Related Domain (GRD): Encoded by exons 21-27a, this domain is homologous to yeast IRA proteins and mammalian p120GAP. It accelerates the intrinsic GTPase activity of RAS proteins by 10⁵-fold, converting active RAS-GTP to inactive RAS-GDP. [3,10]

Other Functional Regions:

• Cysteine-Serine Rich Domain (CSRD): Involved in protein-protein interactions
• Sec14-PH Domain: Membrane localisation and lipid signalling
• C-terminal Domain: Regulation of adenylyl cyclase and cAMP levels

The RAS-MAPK Pathway: Understanding the "Molecular Brake"

The pathophysiology of NF1 centres on loss of RAS regulation:

Normal Physiology:

1. Growth factor binds receptor tyrosine kinase (RTK) on cell surface
2. RTK activation leads to recruitment of SOS (a guanine nucleotide exchange factor)
3. SOS activates RAS by promoting GDP→GTP exchange
4. Active RAS-GTP initiates downstream signalling cascades:
   • RAF→MEK→ERK (MAPK pathway): Cell proliferation, differentiation
   • PI3K→AKT→mTOR pathway: Cell survival, growth, metabolism
5. Neurofibromin (NF1 protein) acts as the "brake"

• accelerating GTP hydrolysis to return RAS to its inactive GDP-bound state

In NF1:

1. Loss of functional neurofibromin removes the "brake"
2. RAS remains in the active GTP-bound state for prolonged periods
3. Sustained activation of MEK/ERK and PI3K/AKT/mTOR pathways
4. Result: Increased cell proliferation, reduced apoptosis, tumourigenesis

This understanding underpins the therapeutic rationale for MEK inhibitors (selumetinib, trametinib) which block downstream signalling despite the upstream RAS hyperactivation. [7,10]

Tumourigenesis: The Two-Hit Model

NF1-associated tumours follow Knudson's two-hit hypothesis:

1. First Hit (Germline): Heterozygous inactivating NF1 mutation present in all cells from conception
2. Second Hit (Somatic): Loss of the remaining wild-type NF1 allele in a specific cell leads to complete loss of neurofibromin function (Loss of Heterozygosity - LOH)
3. Result: Biallelic NF1 inactivation triggers tumour development

This explains why tumours are focal despite the germline mutation being present in every cell. Neurofibromas show biallelic NF1 inactivation primarily in Schwann cells or their precursors. [3]

Haploinsufficiency Effects: Emerging evidence suggests that even single-copy loss (heterozygosity) has functional consequences in certain cell types, particularly:

• Mast cells: Increased infiltration into developing neurofibromas
• Osteoclasts: Bone abnormalities
• Endothelial cells: Vasculopathy [11]

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4. Clinical Presentation

The NIH Diagnostic Criteria (1988) and 2021 Revision

Clinical diagnosis of NF1 requires ≥2 of the following criteria:

Original NIH Criteria (1988)

2021 International Consensus Revisions [6]

Key Changes:

1. Genetic testing now a criterion: A pathogenic heterozygous NF1 variant with a variant allele fraction of 50% in apparently normal tissue (blood, buccal) is diagnostic
2. Choroidal abnormalities added: ≥2 choroidal abnormalities (detected by OCT or NIR imaging) count as an ophthalmic criterion
3. Legius syndrome distinction: SPRED1 mutations excluded - patients with CALMs and freckling ONLY, without other features, should undergo genetic testing

Clinical Diagnostic Algorithm:

                    SUSPECTED NF1
                         ↓
            ≥2 NIH/Consensus Criteria?
                    ↙        ↘
                 YES          NO
                  ↓            ↓
           NF1 DIAGNOSED    Consider:
                           - Genetic testing
                           - Alternative diagnoses
                           - Follow-up surveillance

Detailed Clinical Features

1. Café-au-Lait Macules (CALMs)

Appearance:

• Flat, uniformly hyperpigmented patches
• Colour: Light brown ("coffee with milk") in fair-skinned individuals; darker in pigmented skin
• Borders: Smooth and well-demarcated ("Coast of California")
• Shape: Oval or irregular

Diagnostic Threshold:

• Pre-pubertal: ≥6 spots, each ≥5mm in longest diameter
• Post-pubertal: ≥6 spots, each ≥15mm in longest diameter

Natural History:

• Present at birth or appear within first year of life in > 99% of patients
• May darken with sun exposure
• Tend to fade slightly with age
• First and often only sign in infancy

Histopathology:

• Increased melanin in basal keratinocytes and melanocytes
• Giant melanin granules (macromelanosomes) - though not pathognomonic

Differential Considerations:

• McCune-Albright syndrome: Irregular "Coast of Maine" borders, unilateral distribution
• Legius syndrome: Smooth-bordered CALMs, freckling, but NO neurofibromas or Lisch nodules
• Isolated CALMs: Common in general population (10-20% have 1-2 CALMs)
• Constitutional mismatch repair deficiency: May have NF1-like features plus malignancy

2. Neurofibromas

Neurofibromas are benign peripheral nerve sheath tumours composed of Schwann cells, fibroblasts, perineurial cells, and mast cells within a collagenous matrix.

A. Cutaneous (Dermal) Neurofibromas:

• Arise from terminal nerve branches in the dermis
• Often pruritic
• Continue to increase in number and size throughout life
• Hormonal sensitivity (oestrogen receptors present)

B. Subcutaneous (Nodular) Neurofibromas:

• Arise from larger peripheral nerves
• Present as firm, rubbery nodules along nerve course
• May cause pain or tenderness
• Can grow to significant size

C. Plexiform Neurofibromas:

Key Distinction:

• Plexiform neurofibromas are CONGENITAL (present at birth) though may not be clinically apparent initially
• Cutaneous neurofibromas appear at PUBERTY

Clinical Significance of Plexiform Neurofibromas:

• Grow along length of nerve, involving multiple fascicles
• May cause disfigurement, pain, functional impairment
• Can involve vital structures (airway, great vessels, spine)
• Risk of malignant transformation - the KEY reason for surveillance [8]

3. Axillary/Inguinal Freckling (Crowe's Sign)

• Small (1-3mm) pigmented macules resembling freckles
• Located in intertriginous areas (axillae, groin, infra-mammary, neck folds)
• NOT in sun-exposed areas (distinguishing feature)
• Typically appears age 3-5 years
• Present in > 90% of affected individuals by adulthood
• Highly specific for NF1 when present in classic distribution

4. Optic Pathway Glioma (OPG)

Clinical Presentation:

• Often asymptomatic (detected on screening)
• Visual acuity loss
• Visual field defects
• Proptosis (optic nerve involvement)
• Afferent pupillary defect
• Precocious puberty (chiasmal/hypothalamic involvement)
• Nystagmus (especially in young children)

Natural History:

• Many remain stable or spontaneously regress
• Behaviour less aggressive than sporadic pilocytic astrocytoma
• Progressive visual loss occurs in minority
• Risk of progression highest in children less than 6 years [12]

5. Lisch Nodules

• Iris hamartomas (melanocytic, dome-shaped elevations)
• Tan/brown colour, best seen on slit-lamp examination
• Do NOT affect vision
• Prevalence increases with age:
  • Present in less than 50% of children under 6 years
  • Present in > 90% of adults
• Pathognomonic for NF1 (do not occur in NF2 or Legius syndrome)
• Multiple (typically > 2) required for diagnostic criterion

6. Osseous Lesions

A. Sphenoid Wing Dysplasia:

• Congenital absence or hypoplasia of greater sphenoid wing
• Results in pulsatile exophthalmos (transmitted intracranial pulsations)
• Often associated with ipsilateral plexiform neurofibroma of orbit
• Uncommon (less than 5%) but highly specific

B. Long Bone Abnormalities:

• Tibial Dysplasia (most common): Anterolateral bowing present in infancy
• Progression to fracture and pseudoarthrosis (non-union creating "false joint")
• Affects 2-4% of NF1 patients
• Other bones: fibula, radius, ulna, clavicle
• Usually unilateral
• Congenital in nature

C. Scoliosis:

• Affects 10-30% of patients
• Two types:
  1. Non-dystrophic: Similar to idiopathic scoliosis, less severe curves
  2. Dystrophic: Short, sharp, angular curve; involves fewer vertebrae; higher risk of progression; associated with rib pencilling, vertebral scalloping

7. First-Degree Relative with NF1

• Parent, sibling, or child diagnosed with NF1 by above criteria
• Allows diagnosis in young children with limited manifestations
• The 2021 criteria add genetic confirmation as an alternative

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5. Non-Diagnostic Manifestations

Neurological Complications

Cognitive and Behavioural

• Full-scale IQ is typically within normal limits (mean ~90)
• Specific learning disabilities more common than global intellectual disability
• Executive function impairment affects planning, organisation
• Social cognition difficulties [13]

Brain Tumours (Non-Optic)

• Increased risk of other low-grade gliomas (cerebellum, brainstem)
• Risk of high-grade gliomas increased compared to general population
• Brainstem gliomas: Usually indolent; require monitoring not treatment

Cerebrovascular Disease

• Moyamoya Syndrome: Progressive stenosis of supraclinoid ICA with "puff of smoke" collaterals
• Increased risk of ischaemic stroke
• May be exacerbated by radiation therapy (contraindication to radiotherapy)
• Requires screening in patients with OPG treated with radiotherapy [14]

Other Neurological

• Headaches (migraine and tension-type) - common
• Epilepsy (5-7%)
• Macrocephaly (mean OFC 1-2 SD above mean)
• Aqueductal stenosis (rare but recognised)

Cardiovascular Manifestations

Vasculopathy is an underappreciated feature of NF1:

Clinical Implication: Blood pressure monitoring is essential at every clinical encounter. [11]

Skeletal Manifestations Beyond Diagnostic Criteria

• Short Stature: Mean height approximately -1 SD; macrocephaly gives altered proportion
• Osteoporosis/Osteopenia: Vitamin D metabolism abnormalities; increased fracture risk
• Chest Wall Deformities: Pectus excavatum, pectus carinatum
• Joint Hypermobility

Dermatological

• Juvenile Xanthogranuloma (JXG): Orange-yellow papules; NOT a diagnostic criterion but association noted
• Increased melanocytic naevi
• Glomus tumours (subungual, painful)

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6. Oncological Risks

Malignant Peripheral Nerve Sheath Tumour (MPNST)

MPNST is the most feared complication and leading cause of NF1-related mortality.

Red Flags for MPNST ("The Ugly Duckling"):

• Rapid enlargement of previously stable tumour
• Change from soft to hard consistency
• New or persistent pain (especially nocturnal/rest pain)
• New neurological deficit
• Constitutional symptoms (weight loss, night sweats)

Diagnosis:

• FDG-PET/CT: SUVmax > 3.5 suggests malignancy (sensitivity ~97%, specificity ~72%)
• MRI: Loss of "target sign," irregular margins, heterogeneous enhancement
• Core needle biopsy for histological confirmation

Management:

• Wide surgical excision (only curative option)
• Adjuvant radiation may improve local control
• Chemotherapy (ifosfamide/doxorubicin) for metastatic disease
• Prognosis poor despite treatment [15]

Other Malignancies with Increased Risk in NF1

Breast Cancer Screening: Per National Comprehensive Cancer Network (NCCN) guidelines, women with NF1 should begin annual mammography at age 30, with consideration of breast MRI. [16]

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7. Investigations

Diagnostic Investigations

Clinical Diagnosis

For most patients, NF1 is diagnosed clinically using the revised consensus criteria. No investigations are required if clinical criteria are met.

Genetic Testing

Genetic Testing Performance:

• Mutation detection rate: 95-97% in classic NF1
• Panel testing typically includes NF1, SPRED1 (Legius), and sometimes related genes
• Whole-gene deletion testing essential (MLPA or array CGH)

Ophthalmological Assessment

Imaging

Brain MRI

Indications:

• Symptomatic patients (headaches, seizures, focal deficit)
• Visual abnormalities
• Precocious puberty
• NOT routinely indicated in asymptomatic patients

Findings:

• Optic Pathway Glioma: Fusiform enlargement of optic nerve/chiasm; T1 iso-/hypointense, T2 hyperintense; variable enhancement
• UBOs/FASI: T2 hyperintensities in basal ganglia, cerebellum, brainstem, thalami; no mass effect; no enhancement; regress with age
• Other Gliomas: Brainstem, thalamic (usually low-grade)
• Hamartomas

Whole-Body MRI

• Gold standard for quantifying plexiform neurofibroma burden
• Baseline volumetric assessment for monitoring
• May detect internal plexiform neurofibromas not clinically apparent
• Increasingly used for treatment response monitoring [17]

PET/CT

Indications:

• Suspected MPNST transformation
• Surveillance in high-risk patients (large plexiform neurofibromas)

Interpretation:

• SUVmax > 3.5-4.0: Concerning for malignancy
• SUVmax > 6.0: High specificity for MPNST
• Should prompt tissue diagnosis if clinically feasible

Laboratory Investigations

Skeletal Imaging

• Spine X-ray: Scoliosis assessment; dystrophic features
• Limb X-rays: Tibial bowing, pseudoarthrosis
• DEXA Scan: Bone mineral density assessment in adults

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8. Management

Principles of Care

NF1 management is:

1. Multidisciplinary: Involving neurology, genetics, ophthalmology, dermatology, orthopaedics, oncology, psychology
2. Surveillance-based: Regular monitoring to detect complications early
3. Symptom-directed: Treating manifestations as they arise
4. Supportive: Addressing learning, psychosocial, and cosmetic needs

There is no cure for NF1. The goals are to prevent complications, detect malignancy early, and optimise quality of life.

Management Algorithm

              NF1 DIAGNOSIS CONFIRMED
                       ↓
    ┌──────────────────┼──────────────────┐
    ↓                  ↓                  ↓
SURVEILLANCE       SYMPTOMATIC       TUMOUR-DIRECTED
                   MANAGEMENT         THERAPY
    ↓                  ↓                  ↓
• Annual exam      • ADHD treatment   • Surgery
• BP monitoring    • Learning support • MEK inhibitors
• Eye exam         • Pain management  • Chemotherapy
• Development      • Psychological    • Radiotherapy*
• Scoliosis screen   support          (*avoid if possible)

Surveillance Protocol by Age

Infancy to Age 6 Years

Age 6 Years to Puberty

Adolescence and Adulthood

Specific Management Approaches

Cutaneous Neurofibromas

Indications for Removal:

• Cosmetic distress
• Functional impairment
• Pain, itching, or bleeding
• Catching on clothing

Treatment Options:

Key Point: New neurofibromas will continue to develop throughout life - removal is palliative, not curative.

Plexiform Neurofibromas

Medical Therapy - MEK Inhibitors:

The landmark SPRINT trial (Selumetinib in Pediatric Inoperable plexiform Neurofibromas) established MEK inhibition as standard of care for symptomatic, inoperable plexiform neurofibromas. [7]

Selumetinib:

• FDA approved (April 2020) for children ≥2 years with symptomatic, inoperable plexiform neurofibromas
• EMA approved (June 2021)
• Oral administration, 25 mg/m² twice daily
• Response: 66-70% achieve ≥20% tumour volume reduction
• Durability: Sustained responses with continued treatment

Side Effects:

• Acneiform rash (most common)
• Diarrhoea
• Asymptomatic creatine kinase elevation
• Ocular toxicity (require monitoring)
• Cardiac: LV dysfunction (echocardiogram monitoring)
• Nail paronychia

Other MEK Inhibitors:

• Trametinib: Adult studies ongoing
• Binimetinib: Under investigation

Surgical Management:

• Debulking for symptomatic relief when complete resection not feasible
• Risk of haemorrhage (vascular tumours)
• Risk of functional deficit (nerve involvement)
• Often combined with medical therapy

Optic Pathway Glioma

Observation:

• Most OPGs (especially asymptomatic) can be observed
• Many remain stable or regress spontaneously
• Monitoring: Regular ophthalmology + MRI if symptomatic

Chemotherapy: First-line for progressive, symptomatic OPG:

• Carboplatin + Vincristine: Traditional first-line; response rates 60-70%
• Vinblastine monotherapy: Alternative; less toxic
• MEK inhibitors (Selumetinib): Emerging; NFCTC 2019 showed 47% response rate

Avoid Radiotherapy:

• Radiation is associated with increased risk of:
  • Moyamoya vasculopathy
  • Secondary malignant brain tumours
  • MPNST induction
• Reserved only for progressive disease refractory to chemotherapy [12]

Skeletal Complications

Scoliosis:

• Non-dystrophic: May respond to bracing; surgical fusion if progressive (> 40-50°)
• Dystrophic: High progression risk; earlier surgical intervention often required; posterior fusion ± anterior release

Tibial Pseudoarthrosis:

• Prevention: Protective bracing for bowing before fracture
• Treatment after fracture:
  • Intramedullary rodding
  • Ilizarov external fixation
  • Bone grafting (often with BMP)
  • Bisphosphonates (theoretical benefit)
  • Amputation may be needed if multiple union attempts fail
• Recalcitrant condition with high failure rate

Hypertension

Evaluation:

1. Confirm hypertension on repeat measurements
2. Screen for secondary causes:
   • Plasma metanephrines or urinary catecholamines (phaeochromocytoma)
   • Renal artery Doppler ultrasonography or CT/MR angiography (renal artery stenosis)
3. Treat underlying cause or manage as essential hypertension

Phaeochromocytoma:

• Alpha-blockade (phenoxybenzamine) pre-operatively
• Surgical resection

Renal Artery Stenosis:

• Angioplasty ± stenting
• Surgical revascularisation
• Medical management if not amenable

Cognitive and Behavioural

• Early developmental assessment with intervention services
• Educational support: IEP/504 plans, special education resources
• ADHD: Stimulant medications (methylphenidate) are first-line and effective
• Psychology/psychiatry referral for anxiety, depression
• Social skills training if ASD features present

Genetic Counselling

Essential components:

1. Inheritance explanation: 50% transmission risk to each offspring
2. Variable expressivity: Cannot predict severity in offspring
3. Reproductive options:
   • Natural conception with prenatal testing (CVS/amniocentesis)
   • Preimplantation genetic testing (PGT)
   • Use of donor gametes
   • Adoption
4. Testing of at-risk relatives: Family screening recommended
5. Psychosocial support

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9. Complications Summary

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10. Prognosis

Life Expectancy

• Mean reduction in life expectancy: 10-15 years compared to general population
• Principal causes of death:
  1. Malignant peripheral nerve sheath tumour
  2. Other malignancies
  3. Cardiovascular disease (vasculopathy)
• Overall mortality ratio: 2-3x compared to unaffected siblings [18]

Quality of Life

Major determinants:

• Cosmetic burden: Number and visibility of cutaneous neurofibromas
• Cognitive function: Academic achievement, employment
• Pain: From neurofibromas, skeletal complications
• Psychosocial: Stigma, self-esteem, relationships

Prognostic Factors

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11. Differential Diagnosis

NF1 Mimics and Related Conditions

Key Diagnostic Algorithm

           MULTIPLE CAFÉ-AU-LAIT SPOTS
                      ↓
    ┌─────────────────┼─────────────────┐
    ↓                 ↓                 ↓
Neurofibromas?   Freckling ONLY?    Other features?
  + Lisch?        (no fibromas)     (bone, cardiac)
    ↓                 ↓                 ↓
   NF1          Consider LEGIUS     Consider McCune-
               (test SPRED1)        Albright, Noonan

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12. Evidence and Guidelines

Key Guidelines

Landmark Trials

SPRINT Trial (2020)

Citation: Gross AM, et al. Selumetinib in Children with Inoperable Plexiform Neurofibromas. N Engl J Med. 2020;382(15):1430-1442. [7]

• Design: Phase II, single-arm
• Population: Children 3-17 years with inoperable, symptomatic plexiform neurofibromas
• Intervention: Selumetinib 25 mg/m² twice daily (continuous)
• Primary Endpoint: Objective response (≥20% volume reduction)
• Results:
  • "Overall response rate: 66%"
  • Partial response in 70% of evaluable patients
  • Significant improvement in pain, disfigurement, functional impairment
• Impact: FDA approval (Koselugo™); first-ever approved drug for NF1

SPRINT Stratum 2 (2021)

Citation: Gross AM, et al. Selumetinib in Pediatric Patients with NF1 and Asymptomatic Inoperable Plexiform Neurofibromas at Risk for Complications. The Oncologist. 2022. [19]

• Extended selumetinib indication to asymptomatic but high-risk plexiform neurofibromas

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13. Patient and Family Education

What is NF1?

NF1 is a genetic condition that you are born with. It affects how cells grow in your body, particularly in the skin and nerves. The main features are coffee-coloured birthmarks (café-au-lait spots) and soft bumps under the skin called neurofibromas.

Is NF1 Cancer?

NF1 itself is not cancer. The lumps that grow are almost always benign (not dangerous). However, people with NF1 have a slightly higher chance than average of developing certain types of cancer during their lifetime. This is why regular check-ups are important - to catch anything early when it is most treatable.

Will My Child Have NF1?

If you have NF1, there is a 50% (1 in 2) chance with each pregnancy that your child will inherit the NF1 gene mutation. However, NF1 is very variable - you cannot predict how severe or mild it will be based on your own experience or other family members.

Options for family planning include:

• Natural pregnancy with testing during pregnancy (amniocentesis)
• IVF with testing of embryos before transfer (PGD/PGT)
• Using egg or sperm donation
• Adoption

What Warning Signs Should I Watch For?

Contact your doctor immediately if you notice:

• A lump that is growing quickly or becoming painful
• A lump that changes from soft to hard
• New weakness or numbness in an arm or leg
• Problems with vision
• Persistent headaches, especially with vomiting
• High blood pressure or pounding heart

Is There a Cure?

Currently, there is no cure to "switch off" the gene. However:

• Treatments are available for many of the complications
• A new medication (selumetinib) can shrink the larger nerve tumours
• Research is ongoing, and new treatments are being developed

Living with NF1

• Most people with NF1 lead full, active lives
• Support groups can connect you with others who understand
• Educational support is available for children with learning difficulties
• Cosmetic treatments can reduce the appearance of skin lesions

UK Support: Nerve Tumours UK (www.nervetumours.org.uk) US Support: Children's Tumor Foundation (www.ctf.org) Australia: Children's Tumour Foundation of Australia

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14. Examination Focus

Common Written Exam Questions

Genetics/Paediatrics:

1. Describe the diagnostic criteria for NF1.
2. A 4-year-old has 8 café-au-lait spots and axillary freckling. The mother has similar spots. What is the diagnosis and what surveillance is required?
3. What is the risk of transmission to offspring in NF1?

Neurology:

1. What are the neurological complications of NF1?
2. How do you distinguish NF1 from NF2 clinically?

Oncology:

1. What is the risk of malignant transformation in plexiform neurofibromas?
2. How would you investigate a patient with NF1 and a rapidly enlarging painful mass?

OSCE/Clinical Stations

Skin Station:

• Identify café-au-lait macules, freckling, cutaneous neurofibromas
• Demonstrate "buttonhole sign" of dermal neurofibromas
• Discuss management approach to a patient requesting neurofibroma removal

Eye Station:

• Recognise Lisch nodules on slit-lamp photographs
• Discuss visual surveillance in NF1 children

Viva Questions and Model Answers

Q: Tell me about NF1.

A: "Neurofibromatosis Type 1 is the most common neurocutaneous syndrome, affecting 1 in 3,000 individuals. It is an autosomal dominant disorder caused by mutations in the NF1 tumour suppressor gene on chromosome 17q11.2. This gene encodes neurofibromin, which functions as a RAS-GAP, and loss of function leads to uncontrolled RAS-MAPK signalling. It has complete penetrance but highly variable expressivity. Diagnosis is clinical, requiring two or more of seven criteria: café-au-lait macules, neurofibromas, freckling, Lisch nodules, optic glioma, osseous lesions, or an affected first-degree relative. The 2021 consensus added genetic testing and choroidal abnormalities as criteria."

Q: What are the red flags for MPNST?

A: "The red flags for malignant peripheral nerve sheath tumour in a patient with NF1 are: rapid growth of a previously stable neurofibroma, change in consistency from soft to hard, new or persistent pain especially at rest or at night, new neurological deficit, and constitutional symptoms such as weight loss. Any of these should prompt urgent investigation with FDG-PET/CT and consideration of tissue biopsy."

Q: How does selumetinib work?

A: "Selumetinib is a selective MEK1/2 inhibitor. In NF1, loss of neurofibromin results in constitutive RAS activation and downstream hyperactivation of the RAS-RAF-MEK-ERK (MAPK) pathway. Selumetinib blocks MEK, thereby inhibiting the downstream effects of RAS hyperactivation despite the upstream defect. The SPRINT trial demonstrated that 66% of children with inoperable plexiform neurofibromas achieved objective tumour shrinkage of ≥20%."

Q: Why is radiotherapy relatively contraindicated in NF1?

A: "Radiotherapy is avoided in NF1 patients whenever possible due to the increased risk of radiation-induced complications. These include: moyamoya syndrome from vasculopathy, secondary malignant brain tumours particularly high-grade gliomas, and potentially increased risk of MPNST development. These risks are higher in NF1 patients than in the general population because of the underlying predisposition from haploinsufficient NF1 in vascular and neural cells."

Common Mistakes That Fail Candidates

❌ Confusing NF1 and NF2 (different genes, different tumours) ❌ Not knowing the diagnostic criteria ❌ Stating neurofibromas are malignant (cutaneous neurofibromas have essentially zero malignant potential) ❌ Missing the importance of blood pressure monitoring ❌ Not knowing about the risk of MPNST in plexiform neurofibromas ❌ Recommending routine MRI brain in asymptomatic patients ❌ Not knowing selumetinib and the SPRINT trial

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15. Technical Appendix

Diagnostic Criteria Comparison: 1988 NIH vs 2021 International Consensus

Molecular Testing Interpretation

RAS-MAPK Pathway: Therapeutic Targets

Growth Factor → RTK → RAS-GTP → RAF → MEK → ERK → Cell Proliferation
                        ↑                   ↑
                    Neurofibromin      Selumetinib
                    (NF1 Protein)      Trametinib
                    CONVERTS TO:       BLOCKS
                    RAS-GDP (inactive)

In NF1: Neurofibromin absent → RAS stays active → Uncontrolled proliferation
With MEK inhibitor: Blocks downstream even with RAS hyperactive

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16. References

1. Gutmann DH, Ferner RE, Listernick RH, et al. Neurofibromatosis type 1. Nat Rev Dis Primers. 2017;3:17004. doi:10.1038/nrdp.2017.4

2. Evans DG, Howard E, Giblin C, et al. Birth incidence and prevalence of tumor-prone syndromes: estimates from a UK family genetic register service. Am J Med Genet A. 2010;152A(2):327-332. doi:10.1002/ajmg.a.33139

3. Ratner N, Miller SJ. A RASopathy gene commonly mutated in cancer: the neurofibromatosis type 1 tumour suppressor. Nat Rev Cancer. 2015;15(5):290-301. doi:10.1038/nrc3911

4. Anastasaki C, Gutmann DH. Neuronal NF1/RAS regulation of cyclic AMP requires atypical PKC activation. Hum Mol Genet. 2014;23(25):6712-6721. doi:10.1093/hmg/ddu389

5. Stephens K, Kayes L, Riccardi VM, et al. Preferential mutation of the neurofibromatosis type 1 gene in paternally derived chromosomes. Hum Genet. 1992;88(3):279-282. doi:10.1007/BF00197259

6. Legius E, Messiaen L, Wolkenstein P, et al. Revised diagnostic criteria for neurofibromatosis type 1 and Legius syndrome: an international consensus recommendation. Genet Med. 2021;23(8):1506-1513. doi:10.1038/s41436-021-01170-5

7. Gross AM, Wolters PL, Dombi E, et al. Selumetinib in Children with Inoperable Plexiform Neurofibromas. N Engl J Med. 2020;382(15):1430-1442. doi:10.1056/NEJMoa1912735

8. Hirbe AC, Gutmann DH. Neurofibromatosis type 1: a multidisciplinary approach to care. Lancet Neurol. 2014;13(8):834-843. doi:10.1016/S1474-4422(14)70063-8

9. Pasmant E, Sabbagh A, Spurlock G, et al. NF1 microdeletions in neurofibromatosis type 1: from genotype to phenotype. Hum Mutat. 2010;31(6):E1506-E1518. doi:10.1002/humu.21271

10. Stowe IB, Mercado EL, Stowe TR, et al. A shared molecular mechanism underlies the human rasopathies Legius syndrome and Neurofibromatosis-1. Genes Dev. 2012;26(13):1421-1426. doi:10.1101/gad.190876.112

11. Friedman JM, Arbiser J, Birch PH, et al. Cardiovascular disease in neurofibromatosis 1: report of the NF1 Cardiovascular Task Force. Genet Med. 2002;4(3):105-111. doi:10.1097/00125817-200205000-00002

12. Listernick R, Ferner RE, Liu GT, Gutmann DH. Optic pathway gliomas in neurofibromatosis-1: controversies and recommendations. Ann Neurol. 2007;61(3):189-198. doi:10.1002/ana.21107

13. Hyman SL, Shores A, North KN. The nature and frequency of cognitive deficits in children with neurofibromatosis type 1. Neurology. 2005;65(7):1037-1044. doi:10.1212/01.wnl.0000179303.72345.ce

14. Rosser TL, Vezina G, Packer RJ. Cerebrovascular abnormalities in a population of children with neurofibromatosis type 1. Neurology. 2005;64(3):553-555. doi:10.1212/01.WNL.0000150544.00016.69

15. Kolberg M, Høland M, Agesen TH, et al. Survival meta-analyses for > 1800 malignant peripheral nerve sheath tumor patients with and without neurofibromatosis type 1. Neuro Oncol. 2013;15(2):135-147. doi:10.1093/neuonc/nos287

16. Madanikia SA, Bergner A, Engstrom JE, et al. Increased breast cancer risk in neurofibromatosis type 1: next steps for clinical care. Breast Cancer Res Treat. 2020;182(1):7-13. doi:10.1007/s10549-020-05675-w

17. Plotkin SR, Bredella MA, Cai W, et al. Quantitative assessment of whole-body tumor burden in adult patients with neurofibromatosis. PLoS One. 2012;7(4):e35711. doi:10.1371/journal.pone.0035711

18. Duong TA, Sbidian E, Valeyrie-Allanore L, et al. Mortality associated with neurofibromatosis 1: a cohort study of 1895 patients in 1980-2006 in France. Orphanet J Rare Dis. 2011;6:18. doi:10.1186/1750-1172-6-18

19. Gross AM, Dombi E, Widemann BC. Current status of MEK inhibitors in the treatment of plexiform neurofibromas. Childs Nerv Syst. 2020;36(10):2443-2452. doi:10.1007/s00381-020-04731-2

20. Miller DT, Freedenberg D, Schorry E, et al. Health Supervision for Children With Neurofibromatosis Type 1. Pediatrics. 2019;143(5):e20190660. doi:10.1542/peds.2019-0660

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