Steroid resistant nephrotic syndrome caused by mutation in gene encoding.
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"steroid-resistant nephrotic syndrome" AND "genetic mutations"
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I now have comprehensive data from authoritative nephrology textbooks. Here is the complete answer:
Steroid-Resistant Nephrotic Syndrome (SRNS) - Genetic Causes
SRNS is caused by mutations in genes encoding proteins that maintain the integrity of the glomerular filtration barrier, particularly the podocyte slit diaphragm, podocyte cytoskeleton, and podocyte-GBM adhesion complex. A single-gene cause is identifiable in approximately 25-30% of SRNS cases.
Key Concept: Why These Mutations Cause Steroid Resistance
SRNS due to genetic mutations is not immune-mediated - the defect is structural, affecting the podocyte architecture. Steroids have no effect on a structurally defective slit diaphragm, which explains the resistance.
Genes and Their Encoded Proteins
GROUP 1 - Slit Diaphragm Proteins (Most Common)
| Gene | Protein Encoded | Inheritance | Disease / Notes |
|---|---|---|---|
| NPHS2 | Podocin | AR | Most common genetic cause of childhood SRNS (~18-30% of familial cases). Podocin is a 383-amino acid integral membrane protein at the slit diaphragm. R138Q mutation = severe phenotype; R229Q = late-onset FSGS |
| NPHS1 | Nephrin | AR | Classic congenital nephrotic syndrome (Finnish type); nephrin forms the zipper-like slit diaphragm structure. Over 200 mutations described |
| CD2AP | CD2-associated protein | AR/AD | Scaffolding molecule at slit diaphragm; interacts with nephrin and regulates actin cytoskeleton |
| PLCE1 | Phospholipase C epsilon 1 | AR | Early-onset SRNS with diffuse mesangial sclerosis; important in podocyte development |
| FAT1 | FAT protocadherin 1 | AR | Slit diaphragm component; causes glomerular and tubular ectasia |
| MAGI-2 | Membrane-associated guanylate kinase inverted 2 | AR | Slit diaphragm scaffolding protein; binds nephrin |
GROUP 2 - Podocyte Cytoskeletal Proteins
| Gene | Protein Encoded | Inheritance | Disease / Notes |
|---|---|---|---|
| ACTN4 | Alpha-actinin-4 | AD | Actin cross-linking protein; late-onset proteinuria with slow progression; mutations in the actin-binding domain alter cytoskeletal dynamics |
| INF2 | Inverted formin-2 | AD | Formin (actin regulatory protein); among the most common forms of AD FSGS (>45 mutations); subset also have Charcot-Marie-Tooth disease |
| TRPC6 | Transient receptor potential cation channel 6 | AD | Calcium-permeable cation channel in podocytes; interacts with nephrin and podocin; adult-onset FSGS |
| MYO1E | Myosin 1E | AR | Non-muscle myosin; actin motor protein in podocytes |
GROUP 3 - Podocyte-GBM Adhesion
| Gene | Protein Encoded | Inheritance | Notes |
|---|---|---|---|
| LAMB2 | Laminin beta-2 | AR | GBM component; early-onset; Pierson syndrome (nephrotic syndrome + ocular defects) |
| ITGB4 | Integrin beta-4 | AR | Recessive; associated with epidermolysis bullosa + congenital nephrosis |
| ITGA3 | Integrin alpha-3 | AR | Gain of glycosylation mutation; nephrosis + interstitial lung disease |
| CD151 | Tetraspanin CD151 | AR | Modulates integrin-laminin interactions |
GROUP 4 - Transcription Factors
| Gene | Protein Encoded | Inheritance | Notes |
|---|---|---|---|
| WT1 | Wilms tumor suppressor 1 | AD/AR | Biphasic onset: peaks at 4-12 months AND >18 years; associated with Denys-Drash syndrome and Frasier syndrome |
GROUP 5 - Nuclear Pore Proteins (Rare)
| Gene | Protein Encoded | Inheritance | Notes |
|---|---|---|---|
| NUP93 | Nucleoporin 93 | AR | Recessive early-onset SRNS; can present with microcephaly |
| NUP107 | Nucleoporin 107 | AR | Similar phenotype; links to Galloway-Mowat syndrome |
| NUP205 | Nucleoporin 205 | AR | Early-onset SRNS |
| XPO5 | Exportin-5 | AR | Rare cause of SRNS |
GROUP 6 - Coenzyme Q Biosynthesis (Mitochondrial)
| Gene | Protein Encoded | Notes |
|---|---|---|
| COQ2, COQ6, ADCK4, PDSS2 | CoQ biosynthesis enzymes | Rare mitochondrial causes; importantly, CoQ10 supplementation can help in some CoQ-pathway mutations |
GROUP 7 - Rho GTPase Regulators
| Gene | Protein Encoded | Notes |
|---|---|---|
| ARHGDIA | Rho GDP-dissociation inhibitor alpha | Rare; affects Rho GTPase signaling in podocytes |
Age of Onset Pattern (Clinically Useful)
The chart below shows how gene mutations distribute by age of onset:
Key pattern:
- Neonatal/infantile (0-3 months): NPHS1 (nephrin) - 39.9% of this age group
- Infant to early childhood (0-6 years): NPHS1, LAMB2, PLCE1 - all recessive genes
- Childhood (1-6 years): NPHS2 (podocin) predominates
- Adolescent/young adult: INF2, TRPC6 (dominant genes rise)
- Bimodal: WT1 (peaks at 4-12 months and again >18 years)
- Recessive genes are more common in early-onset disease; dominant genes more common in adult-onset disease
Key Clinical Points
- NPHS2 mutations: Do NOT respond to steroids; treatment is ACE inhibitor/ARB + supportive care; transplant is NOT contraindicated; FSGS does not recur post-transplant
- NPHS1 mutations: FSGS does not recur, but anti-nephrin antibodies can cause proteinuria in the allograft
- Whole-exome sequencing identifies a causal mutation in ~25% of SRNS families across 20+ known genes (Warejko et al., CJASN 2018)
- Genetic SRNS should not receive aggressive immunosuppression (no benefit, potential harm)
Sources: Brenner and Rector's The Kidney, 2-Volume Set; Comprehensive Clinical Nephrology, 7th Edition; Robbins, Cotran & Kumar Pathologic Basis of Disease
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