[5][6] The protein encoded by this gene is a member of the transmembrane 4 superfamily, also known as the tetraspanin family.

The proteins mediate signal transduction events that play a role in the regulation of cell development, activation, growth and motility.

This encoded protein is a cell surface glycoprotein and may have a role in the control of neurite outgrowth.

This gene is associated with X-linked mental retardation and neuropsychiatric diseases such as Huntington's chorea, fragile X syndrome and myotonic dystrophy.

[6] More recently, it has been identified as a key immune system target in type 1 diabetes.