Hereditary Podocytopathies in Adults: The Next Generation

Abstract

Idiopathic nephrotic syndrome may have two underlying mechanisms: either (1) an alteration of the immune system resulting in the production of a putative circulating factor of glomerular permeability; or (2) mutations in the structural genes of the glomerular filtration barrier in which case patients are typically multidrug resistant and do not recur after transplantation. The latter forms have been recently recognized as “hereditary podocytopathies.” In the past few years, positional cloning approaches that allow the identification of gene mutations underlying diseases whose pathophysiology is unknown and animal models have helped decipher the pathophysiological mechanisms of the glomerular filtration process. Recently, the advent of next-generation sequencing (NGS) techniques has greatly facilitated the identification of numerous novel causative genes in hereditary podocytopathies. Moreover, it has revealed mutations in unexpected genes and has widened the phenotypes associated with podocyte gene mutations. The list of genes mutated in hereditary podocytopathies is constantly evolving and consists to date of more than 40 genes. However, the most recently identified genes are extremely rarely mutated and may concern only a couple of families worldwide. These discoveries provided crucial insight into the pathophysiological mechanisms linking podocyte proteins to kidney function. This review will focus on monogenic podocytopathies affecting adult patients.

Rare inherited kidney diseases: an evolving field in Nephrology

“…More than 50 genes related to FSGS have been described so far, most of them related to function or structure of podocytes. The identification of these genes and the understanding of the role of the mutation type in physiopathology and genotype/phenotype characterization have redefined diagnosis, treatment, and prognosis of nephrotic syndrome 11,12 . The genetic causes of FSGS may present as sporadic or familial disease, with autosomal dominant, autosomal recessive, X-linked, or mitochondrial (matrilineal) inheritance patterns.…”

“…Some of the gene mutations (Table 2) that cause childhood and adulthood disease presentation are discussed below. A more detailed review of gene mutations related to FSGS may be found elsewhere 12 . Footnote: #response in heterozygous mutation has been reported; *partial response has been reported.…”

Podocytopathies

“…is usually manifested in childhood as idiopathic steroid resistant nephrotic syndrome (SRNS). For FSGS two main pathogenic mechanisms are assumed: either (1) an alteration of the immune system resulting in the production of a putative circulating glomerular permeability factor; or (2) mutations in more than 50 structural genes of the glomerular filtration barrier, mainly in the podocytes for which they are named hereditary podocytopathies[17]. Genetic mutations that are responsible for non syndromic FSGS include those that encode SD associated and adaptor proteins such as NPHS1, NPHS1+ NPHS2, NPHS2, CD2AP, TRPC6, PTRO, CRB2, PLCe1), actin-based cytoskeleton complex and signaling including at least ACTN4, MYH9, INF2 , MYO1E, ARHGAP24, ARHGDIA and ANLN or nuclear transcriptional factor (WT1)[9,[17][18][19][20][21][22][23][24].…”

“…For FSGS two main pathogenic mechanisms are assumed: either (1) an alteration of the immune system resulting in the production of a putative circulating glomerular permeability factor; or (2) mutations in more than 50 structural genes of the glomerular filtration barrier, mainly in the podocytes for which they are named hereditary podocytopathies[17]. Genetic mutations that are responsible for non syndromic FSGS include those that encode SD associated and adaptor proteins such as NPHS1, NPHS1+ NPHS2, NPHS2, CD2AP, TRPC6, PTRO, CRB2, PLCe1), actin-based cytoskeleton complex and signaling including at least ACTN4, MYH9, INF2 , MYO1E, ARHGAP24, ARHGDIA and ANLN or nuclear transcriptional factor (WT1)[9,[17][18][19][20][21][22][23][24]. Syndromic FSGS may be a consequence of genetic mutations that are responsible for mutations in GBM proteins such as the mutated COL4 genes in Alport syndrome, WT-1in Denys-Drash (DDS) and Frasier syndrome (FS), LMX1B in nail-patella syndrome, metabolic disorders such as GLA, encoding -galactosidase A in Fabry disease, and mitochondriopathies (mitochondrial tRNA mutations in MELAS syndrome, and COQ2 mutations[9,17,18,25].…”

“…Genetic mutations that are responsible for non syndromic FSGS include those that encode SD associated and adaptor proteins such as NPHS1, NPHS1+ NPHS2, NPHS2, CD2AP, TRPC6, PTRO, CRB2, PLCe1), actin-based cytoskeleton complex and signaling including at least ACTN4, MYH9, INF2 , MYO1E, ARHGAP24, ARHGDIA and ANLN or nuclear transcriptional factor (WT1)[9,[17][18][19][20][21][22][23][24]. Syndromic FSGS may be a consequence of genetic mutations that are responsible for mutations in GBM proteins such as the mutated COL4 genes in Alport syndrome, WT-1in Denys-Drash (DDS) and Frasier syndrome (FS), LMX1B in nail-patella syndrome, metabolic disorders such as GLA, encoding -galactosidase A in Fabry disease, and mitochondriopathies (mitochondrial tRNA mutations in MELAS syndrome, and COQ2 mutations[9,17,18,25]. The best-studied susceptibility gene (a genetic variant that represents important risk factors in the presence of a 'second hit') APOL1 (G1 and G2 alleles encoding apolipoprotein L1) is a major cause of podocytopathy among African Americans, formerly called hypertensive chronic kidney disease (CKD)[18].Reactive FSGS occur in CKD with reduced renal mass (e.g., renal dysplasia, surgical renal mass reduction, reflux nephropathy, chronic interstitial nephritis) or in the presence of initially normal renal mass (obesity, sickle cell anemia, or cyanotic congenital heart disease)[9,18].Diffuse mesangial sclerosis is characterized by the presence of dediferented podocyte phenotype (increased expression of cytokeratin) and increased expression of proliferative markers, such as Ki67.…”