Polycystic kidney disease and inherited nephropathies: SAQ

This neonate has the perinatal form of autosomal recessive polycystic kidney disease, confirmed by the homozygous PKHD1 mutation. The bilateral enlarged echogenic kidneys with oligohydramnios, the respiratory distress from pulmonary hypoplasia, and the severe hypertension are the classical presenting features. His thrombocytopenia and splenomegaly indicate congenital hepatic fibrosis with portal hypertension and hypersplenism, which is a defining feature of ARPKD because the PKHD1 gene product fibrocystin is expressed in both the collecting ducts and the biliary epithelium. [2]

Question 1 (10 marks)

Outline your immediate neonatal management and your medium-term surveillance plan for this child, addressing both the renal and hepatic complications. [1]

The immediate priority is respiratory support. The pulmonary hypoplasia from oligohydramnios is the leading cause of neonatal mortality in ARPKD, and he needs continued mechanical ventilation with strategies that accommodate the restricted lung capacity caused by the massively enlarged kidneys splinting the diaphragm. I would involve the neonatal and nephrology teams and plan for prolonged respiratory support. [1]

Severe hypertension is the next priority. His blood pressure of 95 over 65 in a term neonate is significantly elevated, and untreated hypertension in ARPKD can cause cardiac failure, neurological complications and accelerated kidney damage. I would treat with intravenous antihypertensives, titrated carefully because these infants are exquisitely sensitive to volume and blood pressure changes, and then transition to oral agents, typically a calcium channel blocker or beta-blocker, with ACE inhibitor added cautiously once renal function and electrolytes are stable. [1]

Fluid and electrolyte management must account for the polyuria and salt wasting that accompany the impaired concentrating ability of the diseased tubules. I would monitor daily weights, strict input and output, and serum and urine electrolytes closely. Sodium supplementation may be required to maintain intravascular volume and support growth, and I would ensure adequate caloric intake, sometimes via nasogastric feeding, because failure to thrive is a major problem in infantile ARPKD. [2]

For medium-term surveillance, the hepatic fibrosis requires the same attention as the renal disease. His thrombocytopenia and splenomegaly already indicate portal hypertension with hypersplenism, and I would monitor platelet counts, liver function, and abdominal ultrasound with Doppler for portal hypertension at regular intervals. Endoscopic screening for oesophageal varices should begin, because variceal bleeding is a life-threatening complication of congenital hepatic fibrosis. As he grows, I would track his renal function with the estimated GFR, blood pressure, urinalysis and growth parameters, and I would begin planning for the eventuality of renal replacement therapy. If he develops both kidney failure and severe portal hypertension, combined liver-kidney transplantation would be considered, because it addresses both complications simultaneously and has been shown to have favourable outcomes in experienced centres. [3]

Question 2 (10 marks)

Contrast the genetic basis, clinical presentation and disease-specific therapy of autosomal dominant polycystic kidney disease in childhood with Alport syndrome, explaining how genetic testing guides management in each. [2]

Autosomal dominant polycystic kidney disease is caused by mutations in PKD1, encoding polycystin 1, in about 85 percent of cases, or PKD2, encoding polycystin 2, in about 15 percent. The inheritance is autosomal dominant, so one affected parent is usually identified, though de novo mutations occur. In childhood, ADPKD is often detected incidentally when cysts are found on ultrasound performed for a family history, and most children are asymptomatic. The disease mechanism is defective ciliary signalling: polycystin 1 and 2 form a complex on the primary cilium of tubular epithelial cells, and their failure causes cyclic AMP accumulation, cell proliferation and fluid secretion into enlarging cysts. [2]

The disease-specific therapy for ADPKD is tolvaptan, a vasopressin V2 receptor antagonist that reduces cyclic AMP signalling and slows cyst growth. The paediatric randomised controlled trial demonstrated that in children and adolescents aged 4 to 17 years with ADPKD and an estimated GFR of 60 mL per minute per 1.73 square metres or more, tolvaptan slowed the rate of height-adjusted total kidney volume increase over one year. Genetic testing and imaging classification using height-adjusted total kidney volume identify the children at highest risk of rapid progression who are most likely to benefit, because the drug carries the burdens of aquaresis and the risk of hepatotoxicity. Very early-onset ADPKD, with symptoms or significant cyst burden before age 15, is the group where tolvaptan is most likely to be considered. [4]

Alport syndrome is caused by mutations in the type IV collagen genes COL4A5, COL4A3 or COL4A4, which encode the alpha chains forming the specialised network of the glomerular basement membrane, lens capsule and cochlea. The X-linked form from COL4A5 accounts for about 85 percent, and autosomal recessive from biallelic COL4A3 or COL4A4 accounts for about 15 percent. It classically presents in a young boy with persistent microscopic haematuria, episodic gross haematuria with upper respiratory infection, and a family history of hearing loss and kidney failure. The sensorineural hearing loss appears in late childhood or adolescence, affecting high frequencies first. [5]

The disease-specific therapy for Alport syndrome is early ACE inhibitor therapy, and genetic testing is what determines when to start it. The 2020 clinical practice recommendations represent a landmark shift: an ACE inhibitor is now recommended at the time of diagnosis in males with X-linked Alport syndrome and in males and females with autosomal recessive disease, because these patients have the highest risk of rapid progression, and starting before overt proteinuria develops delays the onset of kidney failure by years. In females with X-linked disease and in autosomal dominant disease, treatment starts at the onset of microalbuminuria. This is where genetic testing transforms management: knowing the gene and inheritance pattern, rather than just the clinical picture, determines whether to treat now or to wait and monitor. A boy with a COL4A5 truncating mutation starts an ACE inhibitor today, while a girl with heterozygous COL4A3 is monitored until microalbuminuria appears. [5]

The contrast is instructive. Both are progressive inherited nephropathies, but the defective protein, the mechanism, and the therapy differ fundamentally. ADPKD is a ciliary disease where the therapy targets cyclic AMP signalling with tolvaptan, guided by imaging classification of cyst burden. Alport is a basement membrane disease where the therapy targets the haemodynamic and fibrotic consequences of the fragile filter with an ACE inhibitor, guided by genetic classification of risk. In both, genetic testing is the foundation of precision management, and in both the goal is to delay kidney failure for as long as possible and to reach transplantation in the best possible condition. [2]