SET binding factor 2
The SBF2 gene (also called MTMR13) provides instructions for making a protein called SET binding factor 2. The function of this protein is unknown, but it is probably involved in the development of specialized cells in the nervous system called Schwann cells. Schwann cells produce myelin, the protective substance that covers nerve cells and promotes the rapid transmission of nerve impulses. SET binding factor 2 probably also plays a role in the development of mesh-like canals (trabecular meshwork) that surround the colored part of the eye (the iris). The trabecular meshwork helps drain excess fluid from the eye.
At least five SBF2 gene mutations have been identified in patients with a form of Charcot-Marie-Tooth disease known as type 4B2. Some of these mutations alter the structure of SET binding factor 2 by introducing a premature stop signal that results in an abnormally short protein. Other mutations lead to the production of a protein that is missing a critical segment. All of these mutations probably result in a nonfunctional protein. Although it is unclear how SBF2 gene mutations lead to this disorder, myelin production is probably disrupted. Irregular myelin structure (called outfolding) is a characteristic sign of type 4B2 Charcot-Marie-Tooth disease.
Individuals with this disorder may also experience a buildup of fluid pressure within the eye (glaucoma) beginning in childhood or adolescence. Researchers believe that the appearance of glaucoma depends on the type of SBF2 gene mutation. A mutation that causes complete loss of protein function interferes with the development of the eye's trabecular meshwork, leading to impaired fluid drainage and glaucoma. Less severe mutations, which allow partial function of the SET binding factor 2 protein, do not cause glaucoma.