BackgroundAuditory neuropathy spectrum disorder (ANSD) is a form of hearing loss in which auditory signal transmission from the inner ear to the auditory nerve and brain stem is distorted, giving rise to speech perception difficulties beyond that expected for the observed degree of hearing loss. For many cases of ANSD, the underlying molecular pathology and the site of lesion remain unclear. The X-linked form of the condition, AUNX1, has been mapped to Xq23-q27.3, although the causative gene has yet to be identified.MethodsWe performed whole-exome sequencing on DNA samples from the AUNX1 family and another small phenotypically similar but unrelated ANSD family.ResultsWe identified two missense mutations in AIFM1 in these families: c.1352G>A (p.R451Q) in the AUNX1 family and c.1030C>T (p.L344F) in the second ANSD family. Mutation screening in a large cohort of 3 additional unrelated families and 93 sporadic cases with ANSD identified 9 more missense mutations in AIFM1. Bioinformatics analysis and expression studies support this gene as being causative of ANSD.ConclusionsVariants in AIFM1 gene are a common cause of familial and sporadic ANSD and provide insight into the expanded spectrum of AIFM1-associated diseases. The finding of cochlear nerve hypoplasia in some patients was AIFM1-related ANSD implies that MRI may be of value in localising the site of lesion and suggests that cochlea implantation in these patients may have limited success.

Autosomal dominant non-syndromic hearing loss (ADNSHL) is highly heterogeneous, among them, KCNQ4 is one of the most frequent disease-causing genes. More than twenty KCNQ4 mutations have been reported, but none of them were detected in Chinese mainland families. In this study, we identified a novel KCNQ4 mutation in a five generation Chinese family with 84 members and a known KCNQ4 mutation in a six generation Chinese family with 66 members. Mutation screening of 30 genes for ADNSHL was performed in the probands from thirty large Chinese families with ADNSHL by targeted region capture and high-throughput sequencing. The candidate variants and the co-segregation of the phenotype were verified by polymerase chain reaction (PCR) amplification and Sanger sequencing in all ascertained family members. Then we identified a novel KCNQ4 mutation p.W275R in exon 5 and a known KCNQ4 mutation p.G285S in exon 6 in two large Chinese ADNSHL families segregating with post-lingual high frequency-involved and progressive sensorineural hearing loss. This is the first report of KCNQ4 mutation in Chinese mainland families. KCNQ4, a member of voltage-gated potassium channel family, is likely to be a common gene in Chinese patients with ADNSHL. The results also support that the combination of targeted enrichment and high-throughput sequencing is a valuable molecular diagnostic tool for autosomal dominant hereditary deafness.

Autosomal recessive non‐syndromic hearing loss (ARNSHL) is a highly heterogeneous genetic condition. PDZD7 has emerged as a new genetic etiology of ARNSHL. Biallelic mutations in the PDZD7 gene have been reported in two German families, four Iranian families, and a Pakistani family with ARNSHL. The effect of PDZD7 on ARNSHL in other population has yet to be elucidated. Two Chinese ARNSHL families, each of which had two affected siblings, were included in this study. The families underwent target region capture and high‐throughput sequencing to analyze the exonic, splice‐site, and intronic sequences of 128 genes. Furthermore, 1751 normal Chinese individuals served as controls, and 122 Chinese families segregating with apparent ARNSHL, who had been previously excluded for variants in the common deafness genes GJB2 and SLC26A4, were subjected to screening for candidate mutations. We identified a novel homozygous missense mutation (p.Arg66Leu) and novel compound heterozygous frameshift mutations (p.Arg56fsTer24 and p.His403fsTer36) in Chinese families with ARNSHL. This is the first report to identify PDZD7 as an ARNSHL‐associated gene in the Chinese population. Our finding could expand the pathogenic spectrum and strengthens the clinical diagnostic role of the PDZD7 gene in ARNSHL patients.

A couple with a proband child of GJB2 (encoding the gap junction protein connexin 26)-associated hearing impairment and a previous pregnancy miscarriage sought for a reproductive solution to bear a healthy child. Our study aimed to develop a customized preconception-to-neonate care trajectory to fulfill this clinical demand by integrating preimplantation genetic diagnosis (PGD), noninvasive prenatal testing (NIPT), and noninvasive prenatal diagnosis (NIPD) into the strategy. Auditory and genetic diagnosis of the proband child was carried out to identify the disease causative mutations. The couple then received in-vitro-fertilization treatment, and eight embryos were obtained for day 5 biopsy. PGD was performed by short-tandem-repeat linkage analysis and Sanger sequencing of GJB2 gene. Transfer of a GJB2c.235delC heterozygous embryo resulted in a singleton pregnancy. At the 13th week of gestation, genomic DNA (gDNA) from the trio family and cell-free DNA (cfDNA) from maternal plasma were obtained for assessment of fetal chromosomal aneuploidy and GJB2 mutations. NIPT and NIPD showed the absence of chromosomal aneuploidy and GJB2-associated disease in the fetus, which was later confirmed by invasive procedures and postnatal genetic/auditory diagnosis. This strategy successfully prevented the transmission of hearing impairment in the newborn, thus providing a valuable experience in reproductive management of similar cases and potentially other monogenic disorders.

To report two DFNA5 pathogenic splice-site variations and a novel benign frameshift variation to further support the gain-of-function mechanism of DFNA5 related hearing impairment, targeted genes capture and next generation sequencing were performed on selected members from Family 1007208, 1007081 and a sporadic case with sensorineural hearing loss. Reverse transcriptase polymerase chain reaction was conducted on the proband from Family 1007208 to test how the splice-site variation affects the transcription in RNA level. A novel heterozygous splice-site variation c.991-3 C > A in DFNA5 was found in Family 1007208; a known hotspot heterozygous splice-site variation c.991-15_991_13delTTC was identified in Family 1007081. Both the splice-site variations were segregated with the late onset hearing loss phenotype, leading to the skipping of exon 8 at RNA level. In addition, a novel DFNA5 frameshift variation c.116_119delAAAA was found in the sporadic case, but was not segregated with the hearing impairment phenotype. In conclusion, we identified one novel and one known pathogenic DFNA5 splice-site variation in two Chinese Families, as well as a novel DFNA5 frameshift variation c.116_119delAAAA in a sporadic case, which does not the cause for the hearing loss case. Both the two pathogenic splice-site variations and the nonpathogenic frameshift variation provide further support for the specific gain-of-function mechanism of DFNA5 related hearing loss.