A disease-causing variant of COL4A5 in a Chinese family with Alport syndrome: a case series

Background Alport syndrome (AS), which is a rare hereditary disease caused by mutations of genes including COL4A3, COL4A4 and COL4A5, has a wide spectrum of phenotypes. Most disease-causing variants of AS are located in the exons or the conservative splicing sites of these genes, while little is known about the intronic disease-causing variants. Methods A Chinese AS family was recruited in this study. All the clinical data of AS patient were collected from medical records. After pedigree analysis, the pathogenic variants were studied by the whole exome sequencing (WES). Minigene assay and in vivo RT-PCR analysis were performed to validate the functions of the variants. Results Renal biopsy showed a typical histopathology changes of AS. WES revealed compound heterozygous substitution, NM_033380 c.991–14(IVS17) A > G, in the intron 17 of the COL4A5 gene, which were confirmed by Sanger sequencing. Moreover, the variant was co-segregated with the phenotype in this family. Minigene assay in cultured cell lines showed that a splicing error was induced by this intronic variant, which further confirmed by in vivo RT-PCR analysis. Conclusion A novel intronic disease-causing variant in COL4A5 gene was identified by WES, which was the molecular pathogenic basis of AS.

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

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 ∗ 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.

Implications of a Genetic Etiology for Renal Transplant: Early-Onset Alport Syndrome with a Novel Mutation

Alport's syndrome (AS) is a rare disorder characterized by a triad of deafness, progressive renal dysfunction, and ocular abnormalities. We present a patient of early onset AS with a novel frameshift pathogenic variant in the COL4A5 gene and discuss the utility of genetic testing in the family as well as for the transplant recipient. The patient was a 17-year-old boy with end-stage renal disease (ESRD) and hearing loss. In the setting of ESRD, since hearing loss and anterior lenticonus was detected on an ophthalmologic exam, AS was suspected. On genetic testing, a novel hemizygous frameshift variant was identified in the COL4A5 gene (c.1392del (p.Asp464GlufsTer10)), which was also segregated in the family. In this report, we will discuss the early severe presentation, typical ocular findings, genotype–phenotype correlation, and implications of genetic testing for renal transplant. We will also explore the challenges of genetic testing in developing countries and the potential of pharmacogenomics.