Deciphering the pathogenesis of the COL4-related hematuric nephritis: A genotype/phenotype study

Background Alport syndrome (ATS) is a hereditary progressive hematuric nephropathy associated with sensorineural deafness and ocular abnormalities, which is caused by mutations in the COL4A5 gene (X-linked ATS) and in two autosomal genes, COL4A4 and COL4A3, responsible of both recessive ATS and, when present in heterozygosity, of a spectrum of phenotypes ranging from isolated hematuria to frank renal disease. Methods Retrospective analysis of the clinical and genetic features of 76 patients from 34 unrelated ATS families (11 with mutations in COL4A5, 11 in COL4A3, and 12 in COL4A4) and genotype/phenotype correlation for the COL4A3/COL4A4 heterozygotes (34 patients from 14 families). Results Eight (24%) of the 34 heterozygous COL4A3 and COL4A4 carriers developed renal failure at a mean age of 57 years, with a significantly lower risk than hemizygous COL4A5 or double heterozygous COL4A3/COL4A4 carriers (p < 0.01), but not different from that of the heterozygous COL4A5 females (p = 0.6). Heterozygous carriers of frameshift/splicing variants in COL4A3/COL4A4 presented a higher risk of developing renal failure than those with missense variants in the glycine domains (p = 0.015). Conclusion The renal functional prognosis of patients with COL4A3/COL4A4-positive ATS recapitulates that of the X-linked ATS forms, with differences between heterozygous vs. double heterozygous patients and between carriers of loss-of-function vs. missense variants.

Automated summary

The study retrospectively analyzed the clinical and genetic features of 76 ATS patients from 34 unrelated families and investigated the genotype/phenotype correlation for COL4A3/COL4A4 heterozygotes. The results showed that heterozygous carriers of COL4A3 and COL4A4 had a lower risk of developing renal failure compared to hemizygous COL4A5 or double heterozygous COL4A3/COL4A4 carriers, but not different from heterozygous COL4A5 females.