The HCCS gene helps the mitochondria, the parts of cells that make energy, prepare an important protein for normal cell function. If this gene does not work properly, cells may struggle to manage energy and early development, especially in the eyes and skin. Pathogenic variants in the HCCS gene are linked to a rare condition called microphthalmia with linear skin lesions syndrome, which can cause small or missing eyes and streaky skin changes. This is not a gene that is widely known in popular culture.
What is a gene?
Genes are sections of DNA that hold instructions your cells use to make molecules or manage activities in the body. Some provide the code for proteins, which are the cell’s working parts. Others are mainly involved in regulating when certain processes happen, where they happen, and how active they are. In combination, genes affect how the body grows and works, and they may also influence how you react to food, stress, or medicines. For a deeper look at this subject, visit the LearnHub.
Overview
HCCSGene function
What if the gene works
The HCCS gene helps mitochondria, your cells’ energy centers, make energy. It helps prepare key proteins that let cells use oxygen to release energy from food.
Risk
What if the gene does not work
Variants in the HCCS gene most often cause microphthalmia with linear skin lesions syndrome, with underdeveloped eyes and streaky skin changes present from birth. Milder to more severe variants can also affect brain, heart, and growth, so features vary widely.
Treatment
What does that mean for your treatment
For people with a pathogenic variant in the HCCS gene, no HCCS-specific treatment or management approach is currently established. Treatment choices are supportive and based on a person’s symptoms, not on a distinct drug plan linked to the HCCS gene.
Conditions associated with HCCS
Gene function
What if the gene works
Inside mitochondria, the HCCS gene helps finish two small proteins that cells use to release energy from food. It does this by attaching heme, an iron containing helper, to cytochrome c and cytochrome c1. This step is central to how the HCCS gene helps mitochondria make energy for everyday cell work.
The HCCS gene helps attach heme to cytochrome c and cytochrome c1 inside mitochondria. This finishing step lets these proteins take on their active form.
Active cytochrome c proteins pass electrons through the cell’s energy pathway in mitochondria. This helps cells produce ATP, the main form of usable energy.
By preparing key cytochrome proteins, HCCS supports smooth teamwork among parts of the mitochondrial energy system. This helps many tissues meet steady day to day energy needs.
What is a variant?
A genetic variant is a minor difference in the DNA sequence within a gene. These differences are common and are part of normal human diversity, including variation in appearance, metabolism, and the way the body reacts to environmental influences. Many do not have any noticeable effect and are simply part of natural genetic variation. At times, though, a variant can more significantly change how a gene works and may contribute to, or directly cause, a genetic condition.
Genetic variants
What if the gene does not work
Variants in the HCCS gene can reduce or stop production of a mitochondrial protein that helps switch on key energy-making proteins inside cells. Some variants change the protein’s shape or stability, while more disruptive changes shorten it or stop it from being made at all. This explains how HCCS gene variants affect cell function, with effects ranging from partial loss to near-complete loss of activity. In HCCS-related MLS syndrome, greater loss of activity often links to earlier or more marked features.
How variants are linked to conditions
Pathogenic variants in the HCCS gene cause microphthalmia with linear skin defects syndrome, an X linked condition often called MLS syndrome. In descriptions of HCCS gene variants and microphthalmia with linear skin defects syndrome, the main findings are small or absent eyes and streaky skin changes on the face and neck, with some people also having brain or heart differences. This diagnosis is seen mainly in females, because loss of HCCS is usually not compatible with survival in males.
A variant is not necessarily a diagnosis
Gene variants are a usual part of human biology and are common throughout the general population. Most have no direct impact on health and instead reflect natural human diversity. For many genes, carrying a variant associated with a condition indicates a possible link rather than a definite diagnosis, especially when more than one gene and environmental factors are involved. Still, in some cases, a single well-characterized variant in a particular gene is enough to confirm a diagnosis.
Are there things that can increase or change my risk?
For HCCS-related conditions, risk is mainly determined by whether a harmful change in the HCCS gene is present and whether it is inherited in a family. People assigned female at birth are more often affected, and there is not enough evidence to say that lifestyle changes lower the chance of developing the condition.
Inheritance of HCCS variants
HCCS-related conditions are inherited in an X linked dominant pattern. In practice, how HCCS gene variants are inherited differs for daughters and sons because the HCCS gene sits on the X chromosome. A parent carrying the variant can pass it on with each pregnancy, but this condition is seen mainly in females because affected male pregnancies often do not survive. Many people diagnosed with an HCCS-related condition have a new, de novo variant, meaning it was not inherited from either parent.
What does my HCCS result mean for my family?
For HCCS, the main family pattern is X-linked, so close relatives on the mother’s side may also carry the gene change. Female relatives can sometimes have related features, while male pregnancies are often more severely affected and may not survive. Some HCCS changes happen for the first time in one child, so a parent does not always carry the same result.
Genetic information
Genetic testing
How you find out about variants
Genetic testing for HCCS variants usually uses a blood or saliva sample. A lab reads the HCCS gene to look for small DNA changes and may also check for missing pieces of the gene, which can help confirm an HCCS related diagnosis or clarify whether a familial variant is present.
When should I consider getting a genetic test?
Consider HCCS genetic testing if there is a personal or family history of very small or missing eyes and streaky skin changes present from birth, especially in girls and women. Testing can help confirm the cause of this condition and clarify whether it may run in the family.
A genetic result is only one part of your health story
A genetic result can be informative, but what it can tell you varies based on the condition and the type of variant. Factors like lifestyle, environment, age, and medical history also influence how the body functions over time. For some conditions, particularly those shaped by many genes, genetic information provides context rather than certainty and makes the most sense when considered together with other parts of care. In other situations, a genetic result can give a clear answer. For topics such as medication response, genetic results may help put personal experiences in context.
Pharmacogenetics
How variants shape your response to medicine
Genetic variation can affect how your body responds to medicines. Some people break down a drug more slowly or more quickly than others, while some are more or less sensitive to its effects. This is a common reason the same treatment may work well for one person, cause side effects in another, or seem less helpful in someone else.
What is Pharmacogenetics?
Pharmacogenetics looks at how inherited genetic differences can shape a person’s response to medicines. By examining connections between genes and specific drugs, it helps clarify why the same treatment may work differently from one person to another. For many medications, genes affect both how the body processes a drug and how strongly that drug works. This information can support more informed, individualized treatment choices. You can read more about this topic in the LearnHub.
Drugs influenced by the HCCS gene
When should I seek medical advice?
There is not yet a broadly confirmed role for this gene in predicting how medicines will work, so questions about side effects, new symptoms, or medication choices are best discussed with your doctor or pharmacist.
History
HCCS entered medical genetics through work on a rare inherited condition marked by eye changes and streaks of affected skin, now called microphthalmia with linear skin lesions syndrome. Families and clinicians first recognized the pattern long before the exact gene was known. Initially understood only through visible traits, later recognized as tied to a specific gene, the picture became clearer when researchers mapped the condition to the X chromosome. From these first observations, research expanded steadily. In the mid 2000s, studies identified variants and deletions involving the HCCS gene in affected people, linking earlier clinical reports to a defined genetic cause. That discovery helped bring more precise diagnosis and sharpened understanding of this X linked condition.