Aberrant Splicing of COL4A5 Intronic Variant Contribute to the Pathogenesis of X-Linked Alport Syndrome: A Case Series

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Introduction: X-linked Alport syndrome (XLAS) is caused by pathogenic variants in COL4A5 which lead to abnormalities of the glomerular basement membrane (GBM) structural and is characterized by progressive kidney disease, hearing loss, and ocular abnormalities. The aim of this study was to identify gene mutations in a Chinese family with XLAS by whole-exome sequencing (WES) and verified the pathogenicity of the mutation in vitro experiments. Case Presentation: A five-generation pedigree with a total of 49 family members originating from Hainan province of China was investigated in this study. The proband was a 23-year-old male who developed microscopic hematuria, proteinuria and end-stage kidney disease (ESKD) at age 17. WES identified a novel splicing mutation c.321+5G>A of COL4A5 , which cause exon skip. Further co-segregation analysis confirmed that this mutation exists in relatives who had renal abnormalities using Sanger sequencing. According to American College of Medical Genetics and Genomics guidelines (ACMG), the mutation was determined to be of uncertain significance (VUS). In vitro splicing experiments have shown that the COL4A5 variant induces aberrant mRNA splicing and transcript deletion. Conclusion: We identified a novel intronic COL4A5 pathogenic mutation (c.321+5G>A) in a Chinese XLAS family and described the phenotypes of affected relatives. This study expands the mutation spectrum of COL4A5 gene in XLAS and demonstrates the importance of gene screening for AS. Keywords: Alport syndrome , COL4A5 , whole exome sequencing , mRNA splicing , case series

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