Is This Congenital Nephrotic Syndrome?
Congenital nephrotic syndrome (CNS) is diagnosed when nephrotic-range proteinuria, hypoalbuminemia, and edema manifest in utero or within the first 3 months of life 1.
Diagnostic Criteria
To determine if this is CNS, you must verify:
- Age of onset: Symptoms appearing within the first 3 months of life (0-3 months)
- Classic triad present:
- Nephrotic-range proteinuria (massive urinary protein loss)
- Hypoalbuminemia
- Edema
If symptoms appear between 3-12 months of age, this is classified as infantile nephrotic syndrome (INS), not CNS 2.
Algorithmic Approach to Diagnosis
Step 1: Confirm Timing and Clinical Features
- Document exact age at symptom onset
- Verify presence of proteinuria, hypoalbuminemia, and edema
- Look for prenatal indicators: elevated maternal serum alpha-fetoprotein, large placenta (>25% of birth weight), oligohydramnios, prematurity 1
Step 2: Determine Etiology
Most cases (>90%) are genetic podocytopathies 1. However, you must exclude:
Non-genetic causes to rule out:
- Congenital infections (syphilis, toxoplasmosis, CMV) - check TORCH titers, CMV PCR 3, 4
- Maternal allo-immune disease (anti-neutral endopeptidase antibodies)
- Maternal systemic lupus erythematosus
Genetic causes (most common):
- NPHS1 (nephrin) - most frequent, especially in Finnish populations 1, 5
- NPHS2 (podocin) - more common in INS than CNS 2
- WT1 - associated with syndromic features (genitourinary abnormalities, Wilms tumor risk) 1
- PLCE1, LAMB2 - syndromic forms 1
Step 3: Genetic Testing Strategy
Perform genetic testing immediately - this is now the gold standard for diagnosis 3, 6:
- Next-generation sequencing panel or whole exome sequencing
- Do NOT wait for genetic results to initiate supportive management
- Genetic diagnosis informs prognosis, recurrence risk, and transplant planning
Critical genotype-phenotype associations 2:
- Compound heterozygous NPHS1 mutations (especially c.2335-1 G>A splice mutation) → more severe proteinuria and aggressive course
- Digenic inheritance (NPHS1/WT1 or NPHS1/NPHS2 with triallelic hits) → higher likelihood of requiring transplantation
- NPHS1 mutations → more common in CNS
- NPHS2 and WT1 variants → more common in INS (3-12 months onset)
Step 4: Look for Syndromic Features
Examine for extrarenal manifestations that suggest specific genetic causes:
- Microcephaly + developmental delay → Galloway-Mowat syndrome (OSGEP gene) 7
- Genitourinary abnormalities (ambiguous genitalia, cryptorchidism) → WT1 mutations
- Ocular abnormalities → LAMB2 mutations (Pierson syndrome)
- Neurologic abnormalities → PLCE1 mutations
Common Pitfalls to Avoid
Do not confuse CNS with INS - the 3-month cutoff is critical for classification and has prognostic implications 2
Do not assume all CNS is genetic - always exclude congenital infections, especially in endemic areas or with maternal risk factors 3, 4
Do not delay genetic testing - immunosuppressive therapy is ineffective in genetic CNS and delays definitive diagnosis 8
Do not overlook WT1 mutations - these require early bilateral nephrectomy before transplantation due to Wilms tumor risk 1
Recognize that histopathology alone is insufficient - there is significant disparity between histological appearance, genotype, and clinical severity 9
Prognosis Based on Diagnosis
If confirmed as genetic CNS:
- Most progress to kidney failure within a few years 1
- Kidney transplantation is the only curative therapy 8
- With modern management (albumin supplementation, nutrition optimization, infection prophylaxis, anticoagulation), survival exceeds 90% post-transplant 1
- Outcomes comparable to other pediatric end-stage renal disease causes 8, 9
The definitive answer requires: documented onset within first 3 months of life + nephrotic syndrome features + genetic confirmation or exclusion of infectious/maternal causes.