FAM126A

The FAM126A gene provides instructions for making a protein called hyccin, which is active (expressed) throughout the nervous system. Researchers believe that hyccin is involved in the formation of myelin, which is the covering that protects nerves and promotes the efficient transmission of nerve impulses. Hyccin is also active in the lens of the eye, the heart, and the kidneys; however, the protein's function in these tissues is unclear.

hypomyelination and congenital cataract - caused by mutations in the FAM126A gene

At least four mutations in the FAM126A gene have been found to cause hypomyelination and congenital cataract. Most mutations delete a large portion of the gene or create a premature stop signal in the instructions for making hyccin. These mutations prevent the production of any functional protein. One FAM126A gene mutation allows some protein to be produced. This mutation replaces the protein building block (amino acid) leucine with the amino acid proline at position 53 in the hyccin protein (written as Leu53Pro or L53P). People with the Leu53Pro mutation tend to have milder symptoms than those with mutations that prevent the production of any protein.

Any disruption in the production of hyccin impairs its role in the formation of myelin, leading to neurological problems such as intellectual disability and walking difficulties. It is unclear how a lack of hyccin causes a clouding of the lens (cataract) in both eyes that is typically present from birth in affected individuals. The neurological problems and cataracts are the characteristic features seen in people with hypomyelination and congenital cataract.