Congenital Nephrotic Syndrome: Etiologies and Clinical Features
Congenital nephrotic syndrome (CNS) is predominantly caused by genetic defects in podocyte proteins, with NPHS1 (nephrin) being the most common culprit, though rare cases result from congenital infections or maternal allo-immune disease. 1
Etiologies
Genetic Causes (Primary)
Most cases of CNS are genetic podocytopathies caused by mutations in genes encoding structural proteins of the glomerular filtration barrier 1:
Isolated CNS - Most Common Genes:
- NPHS1 (nephrin): Most frequent cause, particularly in Finnish populations but with genetic heterogeneity in non-Finnish populations 2, 3
- NPHS2 (podocin): More common in infantile nephrotic syndrome (3-12 months) than true CNS 3
- WT1 (Wilms tumor protein 1): Associated with both isolated and syndromic forms
- PLCE1 (NPHS3): Phosphodiesterase ε1 mutations
Syndromic Forms - Key Genes:
- WT1: Associated with genitourinary abnormalities, Denys-Drash syndrome, Frasier syndrome
- LAMB2 (laminin β-2): Causes Pierson syndrome with ocular abnormalities
Important genotype-phenotype correlation: Compound heterozygous NPHS1 mutations, particularly the c.2335-1 G>A splice mutation, are associated with more severe proteinuria (112.4 vs. 53.9 mg/dL) 3. Digenic inheritance patterns (NPHS1/WT1 or NPHS1/NPHS2 with biallelic or triallelic hits) predict more aggressive disease requiring earlier transplantation 3.
Non-Genetic Causes (Rare)
- Congenital infections: Syphilis, toxoplasmosis, cytomegalovirus 4, 5
- Maternal allo-immune disease: Transplacental transfer of maternal antibodies targeting neutral endopeptidase or other kidney proteins 1, 4, 5
- Other rare causes: Maternal systemic lupus erythematosus, mercury poisoning, renal vein thrombosis 4
Clinical Features
Defining Characteristics
CNS manifests in utero or within the first 3 months of life with the classic nephrotic tetrad 1:
- Nephrotic-range proteinuria (massive protein loss)
- Hypoalbuminemia (severe, often <2 g/dL)
- Edema (generalized, often severe)
- Hyperlipidemia/hypercholesterolemia
Prenatal Indicators
Severe Complications (Life-Threatening)
Patients with CNS are prone to multiple severe complications that directly impact mortality 1:
- Haemodynamic instability/collapse: Leading cause of death historically
- Recurrent infections: Second leading cause of death; patients are severely immunocompromised due to immunoglobulin loss
- Thrombotic events: Due to loss of anticoagulant proteins (antithrombin III, protein C/S)
- Impaired growth and failure to thrive: From massive protein and nutrient losses
- Hypothyroidism: From thyroid hormone loss
- Mineral deficiencies: Calcium, vitamin D, iron losses
Disease Progression
Most children with CNS progress to kidney failure within a few years 1. Historical data from Finland (1965-1973) showed mean survival of only 7.6 months (range 0-26 months), with most deaths from infection or hemodynamic collapse 1.
Syndromic Features (Red Flags)
When present, these indicate specific genetic syndromes and warrant immediate genetic testing 6:
- Microcephaly with brain malformations (Galloway-Mowat syndrome) 7
- Genitourinary abnormalities (WT1 mutations)
- Ocular abnormalities (LAMB2/Pierson syndrome)
- Skeletal abnormalities
- Neurodevelopmental delays
- Deafness
- Facial dysmorphisms
Clinical Severity Predictors
Compound heterozygous NPHS1 mutations and digenic inheritance patterns predict more aggressive disease requiring earlier intervention and transplantation 3. The presence of splice site variants, particularly c.2335-1 G>A, correlates with significantly higher proteinuria levels.
Critical Pitfalls
- Do not delay genetic testing: Next-generation sequencing should be performed early to guide prognosis and management 4, 8
- Exclude infections first: Rule out congenital syphilis, toxoplasmosis, and CMV before assuming genetic etiology 4, 5
- Screen for syndromic features: Their presence changes genetic testing strategy and prognosis 6
- Monitor for complications aggressively: Infection and thrombosis are preventable causes of mortality with proper prophylaxis 1