Novel compound heterozygous ATP6V1B1 mutations in a Chinese child patient with primary distal renal tubular acidosis: a case report

Genetic Determinants of Non-Syndromic Enlarged Vestibular Aqueduct: A Review

Hearing loss is the most common sensorial deficit in humans and one of the most common birth defects. In developed countries, at least 60% of cases of hearing loss are of genetic origin and may arise from pathogenic sequence alterations in one of more than 300 genes known to be involved in the hearing function. Hearing loss of genetic origin is frequently associated with inner ear malformations; of these, the most commonly detected is the enlarged vestibular aqueduct (EVA). EVA may be associated to other cochleovestibular malformations, such as cochlear incomplete partitions, and can be found in syndromic as well as non-syndromic forms of hearing loss. Genes that have been linked to non-syndromic EVA are SLC26A4, GJB2, FOXI1, KCNJ10, and POU3F4. SLC26A4 and FOXI1 are also involved in determining syndromic forms of hearing loss with EVA, which are Pendred syndrome and distal renal tubular acidosis with deafness, respectively. In Caucasian cohorts, approximately 50% of cases of non-syndromic EVA are linked to SLC26A4 and a large fraction of patients remain undiagnosed, thus providing a strong imperative to further explore the etiology of this condition.

Identification of seven exonic variants in the SLC4A1, ATP6V1B1, and ATP6V0A4 genes that alter RNA splicing by minigene assay

Primary distal renal tubular acidosis (dRTA) is a rare tubular disease associated with variants in SLC4A1, ATP6V0A4, ATP6V1B1, FOXⅠ1, or WDR72 genes. Currently, there is growing evidence that all types of exonic variants can alter splicing regulatory elements, affecting the precursor messenger RNA (pre-mRNA) splicing process. This study was to determine the consequences of variants associated with dRTA on pre-mRNA splicing combined with predictive bioinformatics tools and minigene assay. As a result, among the 15 candidate variants, 7 variants distributed in SLC4A1 (c.1765C>T, p.Arg589Cys), ATP6V1B1 (c.368G>T, p.Gly123Val; c.370C>T, p.Arg124Trp; c.484G>T, p.Glu162* and c.1102G>A, p.Glu368Lys) and ATP6V0A4 genes (c.322C>T, p.Gln108* and c.1572G>A, p.Pro524Pro) were identified to result in complete or incomplete exon skipping by either disruption of exonic splicing enhancers (ESEs) and generation of exonic splicing silencers, or interference with the recognition of the classic splicing site, or both. To our knowledge, this is the first study on pre-mRNA splicing of exonic variants in the dRTA-related genes. These results highlight the importance of assessing the effects of exonic variants at the mRNA level and suggest that minigene analysis is an effective tool for evaluating the effects of splicing on variants in vitro.

Genotypic and phenotypic analysis in 51 Chinese patients with primary distal renal tubular acidosis

The aim of this study was to analyze the genetic variants of 51 Chinese patients with distal renal tubular acidosis (dRTA) and explore the correlation between their genotype and phenotype. Eight variants of SLC4A1, 19 variants of ATP6V0A4, and 16 variants of ATP6V1B1 have been identified, and of which 14 were novel ones. Eleven patients with autosomal dominant dRTA, and four patients with autosomal recessive dRTA were caused by genetic defects in SLC4A1; 18 and nine patients with recessive dRTA were resulted by defects in ATP6V0A4 and ATP6V1B1 respectively; no causal gene was identified in seven patients. Mutation frequency of SLC4A1 in Chinese populations was more common than Europeans. The incidence of deafness in ATP6V0A4 and ATP6V1B1 groups was 16.7% and 54.5%, respectively. The frequency of CKD in adults, children and infants was 100%, 51%, and 3%, separately. Our study will further expand the mutation spectrum of primary dRTA and provide valuable references to genetic counseling of Chinese populations.