Detecting novel mutations and combined Klinefelter syndrome in Usher syndrome cases

MPZL2-a common autosomal recessive deafness gene related to moderate sensorineural hearing loss in the Chinese population

BACKGROUND

Mutations in MPZL2, the characteristic genetic etiology of autosomal recessive deafness loci 111 (DFNB111), cause non-syndromic and moderate sensorineural hearing loss.

METHODS

In this study, we analyzed the phenotype and genotype of eight pedigrees consisting of 10 hearing loss patients with bi-allelic pathogenic or likely pathogenic variants in MPZL2. These patients were identified from a 3272 Chinese patient cohort who underwent genetic testing.

RESULTS

Apart from symmetrical and moderate sensorineural hearing loss, the MPZL2-related phenotype was characterized by progressive hearing loss with variation in the onset age (congenital defect to onset at the young adult stage). We determined that in the Chinese population, the genetic load of MPZL2 defects was 0.24% (8/3272) in patients diagnosed with hearing loss and 7.02% (8/114) in patients diagnosed with hereditary moderate sensorineural hearing loss caused by STRC, OTOA, OTOG, OTOGL, TECTA, MPZL2 and others. Three known MPZL2 variants (c.220C > T (p.Gln74*), c.68delC (p.Pro23Leufs*2), c.463delG (p.Ala155Leufs*10)) and a novel start loss variant (c.3G > T (p.Met1?)) were identified. MPZL2 c.220C > T was identified as the hotspot variant in the Chinese population and even in East Asia compared with c.72delA (p.Ile24Metfs*22) in European and West Asia through allele frequency.

CONCLUSIONS

We concluded that apart from moderate HL, progressive HL is another character of MPZL2-related HL. No specified variant was verified for the progression of HL, the penetrance and expressivity cannot be determined yet. A novel MPZL2 variant at the start codon was identified, enriching the variant spectrum of MPZL2. The hotspot variants of MPZL2 vary in different ethnicities. This study provides valuable data for the diagnosis, prognosis evaluation and genetic counseling of patients with moderate sensorineural hearing loss related to MPZL2.

Putative Digenic GJB2/MYO7A Inheritance of Hearing Loss Detected in a Patient with 48,XXYY Klinefelter Syndrome

OBJECTIVES

Nonsyndromic hearing loss (NSHL) is the most frequent type of hereditary hearing impairment. Here, we explored the underlying genetic cause of NSHL in a three-generation family using whole-exome sequencing. The proband had concomitant NSHL and rare 48,XXYY Klinefelter syndrome.

MATERIAL AND METHODS

Genomic DNA was extracted from the peripheral blood of the proband and their family members. Sanger sequencing and pedigree verification were performed on the pathogenic variants filtered by whole-exome sequencing. The function of the variants was analyzed using bioinformatics software.

RESULTS

The proband was digenic heterozygous for p.V37I in the GJB2 gene and p.L347I in the MYO7A gene. The proband's mother had normal hearing and did not have any variant. The proband's father and uncle both had NSHL and were compound for the GJB2 p.V37I and MYO7A p.L347I variants, thus indicating a possible GJB2/MYO7A digenic inheritance of NSHL. 48,XXYY Klinefelter syndrome was discovered in the proband after the karyotype analysis, while his parents both had normal karyotypes.

CONCLUSIONS

Our findings reported a putative GJB2/MYO7A digenic inheritance form of hearing loss, expanding the genotype and phenotype spectrum of NSHL. In addition, this is the first report of concomitant NSHL and 48,XXYY syndrome.

Prelingual Sensorineural Hearing Loss Caused by a Novel GJB2 Dominant Mutation in a Chinese Family

Background

GJB2 mutation is the most common cause of genetic deafness. Many pathogenic variations have already been identified, and thus, fewer and fewer novel pathogenic variations remain to be identified. Here, we describe a novel pathogenic variation associated with dominant hereditary deafness in a Chinese family.

Methods

In this study, we examined four generations of a Chinese family (M127) with hearing loss. Temporal CT scan, complete physical examination (including skin and hair), and audiological tests were performed. Targeted next-generation and Sanger sequencing were used to identify pathogenic mutations in affected individuals.

Results

All patients exhibited prelingual nonsyndromic sensorineural hearing loss, with severity ranging from moderate to severe. A novel dominant pathogenic variant c.205T > C (p.Phe69Leu) was identified in all patients in this family.

Conclusions

c.205T > C (p.Phe69Leu) was identified as a novel dominant pathogenic variant of GJB2 associated with prelingual nonsyndromic sensorineural hearing loss.GJB2 mutation is the most common cause of genetic deafness. Many pathogenic variations have already been identified, and thus, fewer and fewer novel pathogenic variations remain to be identified. Here, we describe a novel pathogenic variation associated with dominant hereditary deafness in a Chinese family.