Definition of GJB2
GJB2: A gene that provides instructions to make a protein called gap junction beta 2. Mutations in the GJB2 gene are responsible for autosomal dominant and autosomal recessive forms of nonsyndromic deafness (hearing loss without related signs and symptoms affecting other parts of the body) as well as some other genetic disorders.
The GJB2 gene is a member of the gap junction or connexin family. This family of genes produces protein subunits for channels (gap junctions) that connect neighboring cells. The channels (which are made from several protein subunits) permit the movement of nutrients, charged atoms (ions), and communication signals between cells. The size of the channel opening and the specific particles that move through the channel are determined by the protein subunits that make up the channel. For example, channels made with gap junction beta 2 protein permit the movement of potassium ions, along with other molecules.
Gap junction beta 2 protein is found in cells throughout the body, particularly in the inner ear and the skin. Because of its presence in the inner ear, especially the snail-shaped structure called the cochlea, researchers have focused on the role of this protein in hearing. Hearing requires the conversion of sound waves to electrical nerve impulses. This conversion involves many processes, including maintaining the proper level of potassium ions in the inner ear. Some studies indicate that channels made with gap junction beta 2 protein help to maintain the correct level of potassium ions. Other research suggests that the GJB2 gene is required for the maturation of certain cells in the cochlea. The GJB2 gene also plays a role in the growth and maturation of the outermost layer of skin (epidermis). Mutations in the GJB2 gene cause a number of diseases, including:
Some recessive mutations delete or insert base pairs, the building material of DNA. The most common mutation, particularly in the Caucasian (white) population, deletes 1 base pair between positions 30 and 35 in the gene sequence. This mutation is written as 30delG or 35delG. The deletion results in the production of an extremely short protein, which cannot form proper transport channels. Other deletions are frequently reported in Asian populations (235delC) and among people with an eastern European (Ashkenazi) Jewish ancestry (167delT).
GJB2 mutations can also cause an incorrect replacement of an amino acid (the building material of proteins) in the gap junction beta 2 protein. Substitution mutations can have various effects, including production of an unstable protein that is rapidly broken down, reduced assembly of transport channels, or formation of channels that do not function properly.
Gap junction beta 2 (GJB2) is also known as connexin 26.
Last Editorial Review: 6/14/2012
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