# Unusual phenotype in 35delG mutation: a case report

## TL;DR

This case report describes an unusual hearing loss pattern in a patient with a common GJB2 gene mutation, showing that the expected phenotype may not always occur.

## Contribution

Highlights a rare audiologic manifestation of the 35delG mutation in the GJB2 gene.

## Key findings

- An 18-year-old Turkish female with a heterozygous 35delG mutation showed postlingual, unilateral, progressive hearing loss.
- The observed phenotype deviates from the typical prelingual, bilateral, nonprogressive hearing loss associated with the 35delG mutation.

## Abstract

Mutations in the GJB2 gene, which encodes the protein connexin 26 and is involved in inner ear homeostasis, are identified in approximately 50% of patients with autosomal recessive nonsyndromic hearing loss, making it one of the primary causes of prelingual nonsyndromic hearing loss in various populations. The 35delG mutation, one of the most common mutations of the GJB2 gene, usually causes prelingual, bilateral mild to profound, nonprogressive sensorineural hearing loss.

We present an unusual case of an 18-year-old Turkish female with heterozygous 35delG mutation and postlingual, profound-sloping, progressive and fluctuating unilateral sensorineural hearing loss. The phenotype is different from the usual findings.

The 35delG mutation causing hearing loss may not always be reflected in the phenotype as expected and therefore may have different audiologic manifestations.