[Hearing loss due to mutations or lack of the gene coding protein stereocillin]

[Hearing loss due to mutations in the genes responsible for Usher syndrome]

Usher syndrome is characterized by congenital bilateral sensorineural hearing loss and progressive retinitis pigmentosa, and has an autosomal recessive type of inheritance. The purpose of this work is to summarize the modern data of a clinical picture of Usher syndrome and analyse hearing impairment properties. The frequency of the syndrome among children suffering from hearing loss and deafness is from 3 to 10%. The prevalence of the syndrome in the world is estimated as 4.4 per 100.000 population. The complexity of the diagnosis of the syndrome lies in the significant clinical and genetic heterogeneity. Hearing and vision problems begin at different ages. Primary diagnosis begins with the clinical diagnosis of bilateral hearing loss and visual impairment manifests later. In this case the initial diagnosis of nonsyndromal hearing loss will not be definitive. Molecular genetic studies contribute to the early clinical diagnosis of the syndrome. Understanding the cause of the disease allows to conduct correct medical and genetic counseling and get closer to solving treatment problems.

Genetic etiology of hearing loss in Russia

Prevalence and locus/allelic heterogeneity of the hereditary hearing loss (HL) vary significantly in different human populations. Investigation of the hereditary HL diversity and the evaluation of the factors determining the region-specific landscapes of genetic HL are important for local healthcare and medical genetic services. This review presents the summarized data from the published studies concerning the genetic etiology of HL in different populations of Russia. Multiethnic population of Russia (in total, about 146 million on 2021) includes over 180 different ethnic groups, the number of which varies from millions to just several thousand people. Among them, Russians are the largest group (about 111 million). The contribution of GJB2 gene in the HL etiology in patients of different ethnicities and ethnic-specific prevalence of the GJB2 pathogenic variants were studied in many local populations of Russia. However, the investigation of other "deafness" genes is still limited to a relatively small number of studies on patients with HL of unsolved etiology.

Clinical features of hearing loss caused by STRC gene deletions/mutations in Russian population

Congenital sensorineural hearing loss is related to mutations in numerous genes encoding the structures of the inner ear in majority of the cases. Mutations in GJB2 gene are the most frequently identified causes of congenital nonsyndromal hearing loss. GJB2 gene testing became a routine clinical tool. For GJB2-negative patients new genetic approaches including methods based on new generation sequencing give a chance to identify mutations in other genes. The frequent reason of mild-to-moderate hearing loss such as the deletions/mutations of the gene STRC encoding stereocilin protein were recognized (OMIM: 606440).

OBJECTIVES

To evaluate the audiological features in hearing impaired patients with deletions and point mutations in the STRC gene.

PATIENTS AND METHODS

The group of 28 patients from 21 unrelated families with pathological mutations in the STRC gene underwent audiological examination. The description and analysis of the results of full audiological examination was provided.

RESULTS

All patients initially had bilateral nonsyndromal sensorineural hearing loss. Among 11 homozygotes of large deletion harboring STRC to CATSPER2 genes were 7 male individuals indicating the presence of male infertility syndrome. In general, 7 children failed audiological screening and 4 children underwent audiological assessment in the age of 3 and 6 months. The most frequently hearing thresholds were registered between 35 and 55 dB that corresponds to mild-to-moderate hearing impairment. The average age of diagnostics was 7.9 years (ranged from 3 months to 45 years). In the majority of patients the audiological profiles were flat or descending with elevation of thresholds at middle and high frequencies and relatively preserved thresholds at low frequencies. Hearing thresholds are symmetric and stable with age.

CONCLUSION

STRC-linked hearing loss is congenital, of mild and moderate severity. Special clinical and genetic approach for children who failed newborn hearing screening with mild-to-moderate hearing loss is necessary.