A single-gene cause in 29.5% of cases of steroid-resistant nephrotic syndrome

Abstract

Steroid-resistant nephrotic syndrome (SRNS) is the second most frequent cause of ESRD in the first two decades of life. Effective treatment is lacking. First insights into disease mechanisms came from identification of single-gene causes of SRNS. However, the frequency of single-gene causation and its age distribution in large cohorts are unknown. We performed exon sequencing of NPHS2 and WT1 for 1783 unrelated, international families with SRNS. We then examined all patients by microfluidic multiplex PCR and next-generation sequencing for all 27 genes known to cause SRNS if mutated. We detected a single-gene cause in 29.5% (526 of 1783) of families with SRNS that manifested before 25 years of age. The fraction of families in whom a single-gene cause was identified inversely correlated with age of onset. Within clinically relevant age groups, the fraction of families with detection of the single-gene cause was as follows: onset in the first 3 months of life (69.4%), between 4 and 12 months old (49.7%), between 1 and 6 years old (25.3%), between 7 and 12 years old (17.8%), and between 13 and 18 years old (10.8%). For PLCE1, specific mutations correlated with age of onset. Notably, 1% of individuals carried mutations in genes that function within the coenzyme Q10 biosynthesis pathway, suggesting that SRNS may be treatable in these individuals. Our study results should facilitate molecular genetic diagnostics of SRNS, etiologic classification for therapeutic studies, generation of genotype-phenotype correlations, and the identification of individuals in whom a targeted treatment for SRNS may be available.

Keywords: FSGS; SRNS; genetic disease; kidney failure; nephrosis; steroid-resistant nephrotic syndrome.

Figure 1.

Geographic distribution of the study cohort of 1783 families with SRNS. The number of affected families in the respective countries or cities is represented by the surface area (red) of a circle. Data from countries not represented on the map are shown in the blue box. Insert shows higher resolution of the New York Metropolitan area.

Figure 2.

Age of onset distribution (in years) for 1589 of 1783 examined SRNS families. The displayed 1589 families represent the number of families with available data for age of onset of proteinuria <18 years. (A) Red curve and histograms represent the number of families in each age of onset (years) of SRNS for 1093 families without molecular genetic diagnosis. Blue curve and histograms show number of 496 families with causative mutations identified for each age of onset. (B) Graph indicates percentage of solved families per year of age of onset (from A). Black dotted line represents a binomial fit of age-related percent of families with causative mutation. (Data are not displayed for 72 individuals who were older than 17 years at onset of SRNS and for 122 families with no available information for age of onset. In families with >1 affected family member, the mean age of onset from all affected individuals was used.)

Figure 3.

Detection of the causative mutation in 502 families in an international cohort of 1617 families with SRNS in 21 SRNS-causing genes in relation to age of onset of proteinuria in clinically relevant age groups. The displayed 502 families represent the number of families with detected causative mutation and available data for age of onset of proteinuria <26 years. (A) Percentage of families with causative mutation detected per gene per age group. Histograms indicate fraction (in percentage) of families with causative gene detected in n families per families examined (on top of histograms) per age group. (B) Percentages shown in A are represented by separate bars to highlight distribution across age groups as further delineated in C. Note that mutations in NPHS1 or LAMB2 cause early-onset SRNS, whereas mutations in INF2 or TRPC6 cause late-onset SRNS. (C) Percentages of families with causative mutation detected (from B) are interconnected by lines between age groups and shown in different colors for each causative gene (lower panel for recessive genes, upper panel for dominant genes). NPHS1 mutations (red) have an early age of onset and are rarely found in patients older than 6 years. The dominant genes INF2 and TRPC6 manifest in early adulthood and WT1 (black) shows a biphasic distribution (upper panel). (For families with detected disease-causing mutation, data are not shown for 11 families where no age of onset was available, and for 10 families with an age of onset older than 25 years. For families with no detection of the disease-causing mutation, data are not displayed for 111 families for whom no data for age of onset were available and for 34 families with age of onset older than 25 years. In families with >1 affected family member the mean age of onset from all affected individuals was calculated.).

Figure 4.

Distribution for age of onset of NS in 35 individuals with homozygous mutations in PLCE1. (A) Homozygous PLCE1 mutations are represented by 30 different alleles. The x-axis indicates the mutations sorted by median age of onset. The y-axis indicates the age of onset of SRNS. Symbols are colored red, green, or blue if the allele is truncating, splice, or missense, respectively. (B) Age of onset of SRNS with causative mutations detected in PLCE1, grouped by type of mutation. The x-axis indicates the type of mutations (truncating mutations before amino acid (aa) residue 1000 (N-terminal), truncating mutations after aa residue 1000 (C-terminal), splice and missense mutations. The y-axis indicates the age of onset of proteinuria. Symbols are blue for missense, green for splice, and red for stop and frameshift. Note that the age of onset was significantly different between splice site mutations versus C-terminal truncating mutations (P<0.05), or splice site versus missense mutations (P<0.05). P values are from two-tailed t test. Arrows represent position of outlier values.