A Case Report of Auditory Neuropathy Due to TWNK Gene Mutations

Abstract

Mutations in the TWNK gene were described in patients with Perrault syndrome—an autosomal-recessive disease that includes hearing loss, central auditory and speech disorders, cerebellar ataxia, motor and sensory neuropathy, and ovarian dysfunction. Only around 100 cases of Perrault syndrome have been described to date. Genetically, it caused by biallelic pathologic variants in 1 of 6 genes. A literature review and a case study of Perrault syndrome are given in the article. Two mutations in the TWNK gene were detected in a 13-year-old girl with the phenotype of auditory neuropathy spectrum disorder (ANSD). The nucleotide variant c.1523A>G (p.(Tyr508Cys), NM_021830.5) was previously described; another variant c.1199G>T (p.(Arg400Leu) NM_021830.5) is a new one with an unknown population frequency. The main value of this case is the combination of mutations in the TWNK gene with the phenotype of ANSD, as well as the manifestation of the disease with hearing impairment but without neurological symptoms, unlike what was described in the literature. Specifically, in this case, progression of hearing disorders, ineffective amplification, and limited CI effect were noted. Genetic testing results suggested endocrine system testing, which revealed ovarian dysfunction at a preclinical stage; cerebellar ataxia was also diagnosed. The patient requires further monitoring by a multidisciplinary team.

Keywords: Auditory neuropathy spectrum disorder; cochlear implantation; Perrault syndrome; TWNK gene.

Figure 1.

Initial audiological data (a) Distortion product otoacoustic emissions (DPOAEs), (b) click-auditory brainstem response on stimulus at the level of 100 dB nHL, and (c) pure tone audiogram at the age of 8 years old.

Figure 2.

Electrocochleography results: upper curves—rarefaction and condensation polarities, clear response (cochlear microphonics); lower curves—clamped tube (no response).

Figure 3.

Electrically evoked auditory brainstem response results.

Figure 4.

Sanger sequencing results demonstrating TWNK variants in the compound-heterozygous state in the proband and in the heterozygous state in parents and siblings (marked with arrows).