Autosomal recessive polycystic kidney disease (ARPKD) is a severe, monogenic hepatorenal fibrocystic disorder with an estimated incidence of 1 in 20,000 live births and a carrier frequency of 1:70.
Classic ARPKD is caused by biallelic pathogenic variants in the PKHD1 gene (located on chromosome 6), which encodes fibrocystin/polyductin (FPC), a large protein localized to the primary apical cilium, basal body, and endoplasmic reticulum.
A rare, atypical form of ARPKD is caused by mutations in the DZIP1L gene, presenting with moderate cystic kidney disease but lacking clinically apparent liver involvement.
Pathologically, the kidneys are massively enlarged and feature innumerable microcysts derived from ectatic, dilated collecting ducts radiating from the medulla to the cortex.
ARPKD is a dual-organ disease characterized universally by congenital hepatic fibrosis (CHF) resulting from a ductal plate malformation, leading to bile duct proliferation, progressive hepatic fibrosis, and Caroli syndrome.
Clinical Manifestations
The clinical spectrum is highly variable, with the most severe presentations diagnosed antenatally via the detection of bilaterally enlarged, hyperechoic kidneys and oligohydramnios.
Neonates classically present with Potter sequence (oligohydramnios complex), characterized by pulmonary hypoplasia, flattened nose, micrognathia, low-set ears, and limb-positioning defects, leading to significant perinatal mortality from respiratory failure.
Infants who survive the neonatal period frequently develop severe systemic hypertension requiring aggressive multi-drug therapy within the first few weeks of life.
A subset of patients presents later in infancy or childhood with a predominantly hepatic phenotype, manifesting as portal hypertension, hepatosplenomegaly, gastroesophageal varices, hypersplenism (thrombocytopenia), and recurrent ascending cholangitis.
Hyponatremia is frequently observed in the first weeks of life but is typically transient, while progressive decline in glomerular filtration rate (GFR) leads to end-stage kidney disease (ESKD) in approximately 50% of classical cases by 10 years of age.
Diagnostic Evaluation
Prenatal and postnatal renal ultrasonography demonstrates bilaterally enlarged, reniform kidneys with uniformly increased echogenicity (a “salt and pepper” pattern) and loss of corticomedullary differentiation.
High-resolution ultrasonography may reveal small elliptical cysts arranged radially in the medulla and cortex.
Liver ultrasonography often reveals periportal echogenicity, intrahepatic bile duct dilatation, and macroscopic cysts consistent with Caroli disease.
Diagnosis relies on the modified Zerres criteria, which combine typical renal imaging with clinical/pathological signs of congenital hepatic fibrosis, absence of renal cysts in parents, or a confirmed ARPKD sibling.
Genetic testing with a comprehensive gene panel validates the diagnosis and distinguishes ARPKD from early-onset dominant forms or phenocopies.
Management
Neonatal management is primarily supportive, often requiring aggressive mechanical ventilation for pulmonary hypoplasia and management of spontaneous pneumothorax.
Strict blood pressure control is paramount; renin-angiotensin-aldosterone system (RAAS) blockade with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) serves as first-line therapy.
Severe massive nephromegaly severely restricting diaphragmatic excursion or enteral feeding may necessitate early unilateral or bilateral nephrectomy.
Dialysis (peritoneal or hemodialysis) and eventual kidney transplantation are required for ESKD, and select patients with severe portal hypertension or recurrent cholangitis may require combined liver-kidney transplantation.
Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary kidney disease, affecting 1 in 400 to 1,000 individuals, and accounts for nearly 5% of all ESKD cases.
The disorder is genetically heterogeneous; approximately 78% of cases are caused by mutations in the PKD1 gene (chromosome 16p13.3) encoding polycystin-1 (PC1), and 15% by mutations in the PKD2 gene (chromosome 4q22) encoding polycystin-2 (PC2).
Emerging atypical genetic variants causing ADPKD include mutations in GANAB, DNAJB11, and ALG9, which often present with mild renal enlargement but significant interstitial fibrosis or polycystic liver disease.
A contiguous gene deletion syndrome involving adjacent TSC2 and PKD1 genes causes a severe, very early-onset cystic phenotype with features of tuberous sclerosis.
Pathophysiologically, defective polycystin function in the primary cilium alters intracellular calcium homeostasis, increases cyclic AMP (cAMP) levels, and upregulates the mechanistic target of rapamycin (mTOR) pathway.
These cellular alterations drive abnormal tubular epithelial cell proliferation, fluid secretion (mediated by CFTR channels), and continuous cyst expansion from any segment of the nephron.
Clinical Manifestations in Childhood
While ADPKD is traditionally considered an adult-onset disease, progressive structural kidney damage (cyst formation and kidney enlargement) begins in utero or early childhood.
Hypertension is a frequent and early manifestation in children, affecting 20-40% of pediatric patients, and is associated with larger Total Kidney Volume (TKV) and faster disease progression.
Masked hypertension and loss of nocturnal blood pressure dipping are common, making 24-hour ambulatory blood pressure monitoring (ABPM) a critical evaluation tool in pediatric ADPKD.
Macroscopic or microscopic hematuria may occur due to cyst hemorrhage, nephrolithiasis, or urinary tract infections.
Impaired urinary concentrating capacity leads to early polyuria, polydipsia, and nocturnal enuresis.
Extrarenal manifestations include an increased left ventricular mass index (LVMI), early vascular dysfunction (increased pulse wave velocity), and mitral valve prolapse.
Very Early Onset (VEO) ADPKD, diagnosed before 18 months of age, presents with massive nephromegaly and hypertension, mimicking ARPKD, and carries a high risk of progression to ESKD in childhood.
Diagnosis
Renal ultrasonography is the primary screening modality, demonstrating bilaterally enlarged kidneys with multiple distinct macrocysts.
For at-risk individuals aged 15 to 39 years with a positive family history, the presence of three or more unilateral or bilateral kidney cysts is sufficient for establishing an ADPKD diagnosis.
Total Kidney Volume (TKV) measured via Magnetic Resonance Imaging (MRI) is the most reliable biomarker for predicting the risk of functional decline and chronic kidney disease progression.
In families without a known history (de novo mutations occur in 8-10% of cases) or in children with VEO ADPKD, genetic panel testing is strongly advised to differentiate from ARPKD and other ciliopathies.
Management
Lifestyle modifications include high water intake to suppress endogenous arginine vasopressin (AVP) production, dietary sodium restriction, and maintaining a normal body mass index.
Strict blood pressure control is paramount to slow cardiovascular and renal progression; ACE inhibitors or ARBs are the preferred first-line agents, targeting a blood pressure below the 50th to 75th percentile for age, sex, and height.
Tolvaptan, a vasopressin V2 receptor antagonist, decreases cAMP levels and has been shown to reduce TKV growth and GFR decline in rapidly progressive adult ADPKD; pediatric clinical trials are currently underway.
Pravastatin (an HMG-CoA reductase inhibitor) has demonstrated efficacy in significantly slowing the progression of height-adjusted TKV in children and young adults with ADPKD.