HCCS

The HCCS gene carries instructions for producing an enzyme called holocytochrome c-type synthase. This enzyme is active in many tissues of the body and is found in the mitochondria, the energy-producing centers within cells.

Within the mitochondria, the holocytochrome c-type synthase enzyme helps produce a molecule called cytochrome c. Specifically, holocytochrome c-type synthase is involved in a reaction that adds an iron-containing molecule called heme to make mature cytochrome c, also called holocytochrome c, from a precursor form called apocytochrome c.

Cytochrome c is involved in a process called oxidative phosphorylation, by which mitochondria generate adenosine triphosphate (ATP), the cell's main energy source. It also plays a role in the self-destruction of cells (apoptosis).

microphthalmia with linear skin defects syndrome - caused by mutations in the HCCS gene

At least three HCCS gene mutations have been identified in individuals with microphthalmia with linear skin defects syndrome. Deletions of genetic material that include the HCCS gene have also been identified in affected individuals. HCCS gene mutations result in a holocytochrome c-type synthase enzyme that cannot perform its function. A deletion of genetic material that includes the HCCS gene prevents the production of the enzyme from that copy of the gene. This loss of functional holocytochrome c-type synthase enzyme can damage cells by impairing their ability to generate energy. In addition, without sufficient holocytochrome c-type synthase enzyme, the damaged cells may not be able to undergo apoptosis. These cells may instead die in a process called necrosis that causes inflammation and damages neighboring cells. During early development this spreading cell damage may lead to the eye and skin abnormalities characteristic of microphthalmia with linear skin defects syndrome.