Microphthalmia with linear skin defects syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Microphthalmia with linear skin defects syndrome is a disorder that mainly affects females. In people with this condition, one or both eyes may be very small or poorly developed (microphthalmia). Affected individuals also typically have unusual linear skin markings on the head and neck. These markings follow the paths along which cells migrate as the skin develops before birth (lines of Blaschko). The skin defects generally improve over time and leave variable degrees of scarring.

The signs and symptoms of microphthalmia with linear skin defects syndrome vary widely, even among affected individuals within the same family. In addition to the characteristic eye problems and skin markings, this condition can cause abnormalities in the brain, heart, and genitourinary system. A hole in the muscle that separates the abdomen from the chest cavity (the diaphragm), which is called a diaphragmatic hernia, may occur in people with this disorder. Affected individuals may also have short stature and fingernails and toenails that do not grow normally (nail dystrophy).

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the HCCS gene or a deletion of genetic material on the X chromosome that includes the HCCS gene cause microphthalmia with linear skin defects syndrome. 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. 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).

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. A lack of functional holocytochrome c-type synthase enzyme can damage cells by impairing their ability to generate energy. In addition, without the 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 abnormalities and other signs and symptoms of microphthalmia with linear skin defects syndrome.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an X-linked dominant pattern. The gene associated with this condition is located on the X chromosome, which is one of the two sex chromosomes. In females (who have two X chromosomes), a mutation in one of the two copies of the gene in each cell is sufficient to cause the disorder. Some cells produce a normal amount of the holocytochrome c-type synthase enzyme and other cells produce none. The resulting overall reduction in the amount of this enzyme leads to the signs and symptoms of microphthalmia with linear skin defects syndrome.

In males (who have only one X chromosome), mutations result in a total loss of the holocytochrome c-type synthase enzyme. A lack of this enzyme appears to be lethal very early in development, so almost no males are born with microphthalmia with linear skin defects syndrome. A few affected individuals with male appearance but who have two X chromosomes have been identified.

Most cases of microphthalmia with linear skin defects syndrome occur in people with no history of the disorder in their family. These cases usually result from the deletion of a segment of the X chromosome during the formation of reproductive cells (eggs and sperm) or in early fetal development. They may also result from a new mutation in the HCCS gene.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

The prevalence of microphthalmia with linear skin defects syndrome is unknown. More than 50 affected individuals have been identified.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormality of skin pigmentation · Very frequent (99-80%)

An abnormality of the pigmentation of the skin.

Anophthalmia · Very frequent (99-80%)

Absence of the globe or eyeball.

Congenital diaphragmatic hernia · Very frequent (99-80%)

The presence of a hernia of the diaphragm present at birth.

Corneal opacity · Very frequent (99-80%)

A reduction of corneal clarity.

Dermal atrophy · Very frequent (99-80%)

Partial or complete wasting (atrophy) of the skin.

Erythema · Very frequent (99-80%)

Redness of the skin, caused by hyperemia of the capillaries in the lower layers of the skin.

Hyperpigmentation of the skin · Very frequent (99-80%)

A darkening of the skin related to an increase in melanin production and deposition.

Microphthalmia · Very frequent (99-80%)

A developmental anomaly characterized by abnormal smallness of one or both eyes.

Other findings in the same source

From: Orphanet

Additional reported features include Midface retrusion (Very frequent (99-80%)); Sclerocornea (Very frequent (99-80%)); Aplasia/Hypoplasia of the skin (Very frequent (99-80%)); Abnormal cardiac septum morphology (Frequent (79-30%)); Abnormal eyelash morphology (Frequent (79-30%)); Abnormal eyelid morphology (Frequent (79-30%)); Abnormal facial shape (Frequent (79-30%)); Abnormal nasolacrimal system morphology (Frequent (79-30%)); Abnormal vitreous humor morphology (Frequent (79-30%)); Abnormality of retinal pigmentation (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Microphthalmia with linear skin defects syndrome is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

Additional services that may be relevant, depending on the findings, include: Dermatology.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Microphthalmia with linear skin defects syndrome. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.