HID is a rare disorder. Its prevalence is unknown.

HID is caused by mutations in the GJB2 gene. This gene provides instructions for making a protein called gap junction beta 2, more commonly known as connexin 26. Connexin 26 is a member of the connexin protein family. Connexin proteins form channels called gap junctions that permit the transport of nutrients, charged atoms (ions), and signaling molecules between neighboring cells that are in contact with each other. Gap junctions made with connexin 26 transport potassium ions and certain small molecules.

Connexin 26 is found in cells throughout the body, including the inner ear and the skin. In the inner ear, channels made from connexin 26 are found in a snail-shaped structure called the cochlea. These channels may help to maintain the proper level of potassium ions required for the conversion of sound waves to electrical nerve impulses. This conversion is essential for normal hearing. In addition, connexin 26 may be involved in the maturation of certain cells in the cochlea. Connexin 26 also plays a role in the growth and maturation of the outermost layer of skin (the epidermis).

At least one GJB2 gene mutation has been identified in people with HID. This mutation changes a single protein building block (amino acid) in connexin 26. The mutation is thought to result in channels that constantly leak ions, which impairs the health of the cells and increases cell death. Death of cells in the skin and the inner ear may underlie the signs and symptoms of HID.

Because the GJB2 gene mutation identified in people with HID also occurs in keratitis-ichthyosis-deafness syndrome (KID syndrome), a disorder with similar features and the addition of eye abnormalities, many researchers categorize KID syndrome and HID as a single disorder, which they call KID/HID. It is not known why some people with this mutation have eye problems while others do not.