A 60-year-old man was referred to the ENT department for intense episodic vertigo triggered by loud sounds. Pure tone audiometry and otoneurological assessment, including videonystagmography using auditory stimulation and cervical vestibular evoked myogenic potential measures, conducted to the hypothesis of a third window syndrome in the left ear. Results from the high-resolution computed tomography of the petrous bone confirmed the hypothesis and revealed the presence of a submillimeter semicircular canal dehiscence, located between the left lateral and superior semicircular canal ampullae on the left side.

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Although etiologically heterogeneous at least 50% of all early on-set hearing losses have a genetic cause and of these, the large majority, 75-80% are most probably autosomal recessive and 70% are non-syndromic. The rest of the congenital hearing losses are determined by clinical and environmental factors such as ototoxic medication, prematurity, and complications at birth. During the last decade it became clear that 50-80% of all such afflictions result from mutations in a single gene, GJB2, which encodes the protein Connexin 26. In order to, at least partially clarify this problem, especially in an emerging country such as Romania, where the problem is not studied adequately, we developed a comprehensive study of genetic, clinical and environmental risk factors for congenital hearing loss. The two most common variations of this gene, 35delG and W24X in children with positive diagnosis of bilateral severe to profound sensorineural hearing loss were investigated. A cohort of 34 children (20 female and 14 male), ages between 2 and 10 (mean age 4.62 years), coming from 33 non-related families were evaluated. All cases were diagnosed with severe or profound bilateral congenital SNHL. A statistical comparison of genetic and environmental/clinical prevalence was also attempted since the presence of a genetic disorder cannot rule out the role of other documented risk factors in the etiology of SNHL. The results showed that, 29.4% of cases (10/34) were homozygotic for the 35delG mutation 35delG/35delG), also known as genotype Δ/Δ. 5.88% of cases (2/34) belong to the heterozygotic bi-genic group 35delG/W24X. The clinical factors with high statistical significance for SNHL in a non-genetic group have no significance for genetic SNHL patients. Thus, the present study confirms the relatively high prevalence of the 35delG and W24X mutations in cases of congenital non-syndromic severe of profound bilateral SNHL.

(1) Background: In this paper, we report on three cases of hypoacusis as part of a complex phenotype and some rare gene variants. An extensive review of literature completes the newly reported clinical and genetic information. (2) Methods: The cases range from 2- to 11-year-old boys, all with a complex clinical picture and hearing impairment. In all cases, whole exome sequencing (WES) was performed, in the first case in association with mitochondrial DNA study. (3) Results: The detected variants were: two heterozygous variants in the TWNK gene, one likely pathogenic and another of uncertain clinical significance (autosomal recessive mitochondrial DNA depletion syndrome type 7—hepatocerebral type); heterozygous variants of uncertain significance PACS2 and SYT2 genes (autosomal dominant early infantile epileptic encephalopathy) and a homozygous variant of uncertain significance in SUCLG1 gene (mitochondrial DNA depletion syndrome 9). Some of these genes have never been previously reported as associated with hearing problems. (4) Conclusions: Our cases bring new insights into some rare genetic syndromes. Although the role of TWNK gene in hearing impairment is clear and accordingly reflected in published literature as well as in the present article, for the presented gene variants, a correlation to hearing problems could not yet be established and requires more scientific data. We consider that further studies are necessary for a better understanding of the role of these variants.

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