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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed October 2009

What is the official name of the HCCS gene?

The official name of this gene is “holocytochrome c synthase.”

HCCS is the gene's official symbol. The HCCS gene is also known by other names, listed below.

What is the normal function of the HCCS gene?

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).

How are changes in the HCCS gene related to health conditions?

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.

Where is the HCCS gene located?

Cytogenetic Location: Xp22.3

Molecular Location on the X chromosome: base pairs 11,111,286 to 11,123,086

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The HCCS gene is located on the short (p) arm of the X chromosome at position 22.3.

The HCCS gene is located on the short (p) arm of the X chromosome at position 22.3.

More precisely, the HCCS gene is located from base pair 11,111,286 to base pair 11,123,086 on the X chromosome.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about HCCS?

You and your healthcare professional may find the following resources about HCCS helpful.

You may also be interested in these resources, which are designed for genetics professionals and researchers.

What other names do people use for the HCCS gene or gene products?

  • CCHL
  • DKFZp779I1858
  • holocytochrome c synthase (cytochrome c heme-lyase)
  • MCOPS7

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding HCCS?

adenosine triphosphate ; apoptosis ; ATP ; cell ; deletion ; enzyme ; gene ; heme ; inflammation ; iron ; mitochondria ; molecule ; necrosis ; oxidative phosphorylation ; phosphorylation ; precursor ; syndrome

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • NCBI Gene (
  • Prakash SK, Cormier TA, McCall AE, Garcia JJ, Sierra R, Haupt B, Zoghbi HY, Van Den Veyver IB. Loss of holocytochrome c-type synthetase causes the male lethality of X-linked dominant microphthalmia with linear skin defects (MLS) syndrome. Hum Mol Genet. 2002 Dec 1;11(25):3237-48. (
  • Wimplinger I, Morleo M, Rosenberger G, Iaconis D, Orth U, Meinecke P, Lerer I, Ballabio A, Gal A, Franco B, Kutsche K. Mutations of the mitochondrial holocytochrome c-type synthase in X-linked dominant microphthalmia with linear skin defects syndrome. Am J Hum Genet. 2006 Nov;79(5):878-89. Epub 2006 Sep 6. (
  • Wimplinger I, Shaw GM, Kutsche K. HCCS loss-of-function missense mutation in a female with bilateral microphthalmia and sclerocornea: a novel gene for severe ocular malformations? Mol Vis. 2007 Aug 27;13:1475-82. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: October 2009
Published: February 8, 2016