Novel Mutations of COL4A5 Identified in Chinese Families with X-Linked Alport Syndrome and Literature Review

Abstract

Alport syndrome (AS) is an inherited kidney disease caused by defects in type IV collagen, which is characterized by hematuria, progressive nephritis or end-stage renal disease (ESRD), hearing loss, and occasionally ocular lesions. Approximately 80% of AS cases are caused by X-linked mutations in the COL4A5 gene. This study explored novel deletion and missense mutations in COL4A5 responsible for renal disorder in two Han Chinese families. In pedigree 1, the five male patients all had ESRD at a young age, while the affected female members only presented with microscopic hematuria. Whole exome sequencing and Sanger sequencing identified a novel frameshift deletion mutation (c.422_428del, p.Leu142Valfs$\ast$11) in exon 7 of COL4A5. In pedigree 2, the 16-year-old male proband had elevated serum creatinine (309 μmol/L) without extrarenal manifestations, while his mother only manifested with hematuria. A missense mutation (c.476G>T, p.Gly159Val) was found in exon 9 of the COL4A5 gene. Neither of these mutations was present in the Exome Variant Server of the NHLBI-ESP database, nor was it found in the ExAC or 1000 Genomes databases. Through the literature review, it was found that male Chinese patients with X-linked AS carried COL4A5 deletion or missense mutations had a more severe phenotype than female patients, particularly in proteinuria and impaired renal function. Compared to male patients with missense mutations, patients in whom deletion mutations were found were more likely to progress to ESRD (15.4% vs. 36.0%,$P=0.041$). This study identified two novel COL4A5 mutations in Chinese families with X-linked AS, expanded the mutational spectrum of the COL4A5 gene, and presented findings that are significant for the screening and genetic diagnosis of AS.