CPT® Code 81254

GJB6 (gap junction protein, beta 6, 30kDa, connexin 30) (eg, nonsyndromic hearing loss) gene analysis, common variants (eg, 309kb [del(GJB6-D13S1830)] and 232kb [del(GJB6-D13S1854)])

Molecular genetic testing, specifically for the GJB6 gene, is conducted to identify mutations that lead to nonsyndromic hearing loss. The GJB6 gene encodes for gap junction proteins, also known as connexin proteins, which are essential for the transport of nutrients, ions, and signaling molecules between adjacent cells. Connexin 30, the protein produced by the GJB6 gene, is particularly important in the functioning of cells located in the brain, skin, and inner ear, specifically within the cochlea. This gene is situated on chromosome 13 and plays a critical role in auditory function. Nonsyndromic deafness, referred to as NFNB1, is an autosomal recessive condition, meaning that an individual must inherit two mutated copies of the gene to exhibit the hearing loss associated with this disorder. Carriers, who possess only one mutated gene, typically do not show symptoms. In certain instances of NFNB1, both copies of the GJB6 gene may experience a deletion of a protein, indicating a monogenic inheritance pattern. Alternatively, a digenic inheritance pattern may occur, where one copy of the GJB6 gene is deleted while a different mutation exists on the neighboring GJB2 gene, leading to impaired function of the gap junctions, reduced potassium levels, and subsequent hearing loss. These genetic mutations disrupt the process of converting sound waves into nerve impulses, which is essential for hearing. Additionally, a less common form of nonsyndromic deafness, known as DFNA3, is characterized as an autosomal dominant disorder, requiring only one altered copy of the GJB6 gene. In this case, a specific amino acid change occurs, where threonine is replaced by methionine at position 5 (Thr5Met), which negatively impacts the activity of the gap junction and affects potassium levels within the cells.