Harlequin ichthyosis

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Harlequin ichthyosis is a severe genetic disorder that affects the skin. Infants with this condition are born prematurely with very hard, thick skin covering most of their bodies. The skin forms large, diamond-shaped plates that are separated by deep cracks (fissures). These skin abnormalities affect the shape of the eyelids, nose, mouth, and ears, and limit movement of the arms and legs. Restricted movement of the chest can lead to breathing difficulties and respiratory failure in babies with harlequin ichthyosis. Affected infants also have feeding problems.

The skin normally forms a protective barrier between the body and its surrounding environment. The skin abnormalities associated with harlequin ichthyosis disrupt this barrier, making it difficult for affected infants to control water loss, regulate their body temperature, and fight infections. Infants with harlequin ichthyosis often experience an excessive loss of fluids (dehydration) and develop life-threatening infections in the first few weeks of life.

Following the newborn period, the hard, skin plates are shed and the skin develops widespread scales and redness.

It used to be very rare for affected infants to survive the newborn period. However, with intensive medical support and improved treatment, babies with this disorder now have a better chance of living into childhood and early adulthood.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Variants (also known as mutations) in the ABCA12 gene cause harlequin ichthyosis. The ABCA12 gene provides instructions for making a protein that is essential for the normal development of skin cells. This protein plays a major role in the transport of fats (lipids) and enzymes in the outermost layer of skin (the epidermis).

Some variants in the ABCA12 gene prevent the cell from making any ABCA12 protein. Other variants lead to the production of an abnormally small version of the protein that cannot transport lipids properly. A loss of functional ABCA12 protein disrupts the normal development of the epidermis before and after birth, resulting in the severe skin abnormalities characteristic of harlequin ichthyosis.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have variants. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Harlequin ichthyosis is very rare; its exact incidence is unknown.

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.

Congenital ichthyosiform erythroderma · Very frequent (99-80%)

An ichthyosiform abnormality of the skin with congenital onset.

Depressed nasal ridge · Very frequent (99-80%)

Lack of prominence of the nose resulting from a posteriorly-placed nasal ridge.

Ectropion · Very frequent (99-80%)

An outward turning (eversion) or rotation of the eyelid margin.

Hearing abnormality · Very frequent (99-80%)

An abnormality of the sensory perception of sound.

Hyperkeratosis · Very frequent (99-80%)

Hyperkeratosis is a histopathological term defining a thickened stratum corneum and may be present in many different skin conditions, with many possible overlaps. Hyperkeratosis refers to the increased thickness of the stratum corneum, the outer layer of the skin. Hyperkeratosis is subclassified as orthokeratotic or parakeratotic. Orthokeratotic hyperkeratosis refers to the thickening of the keratin layer with preserved keratinocyte maturation, while parakeratotic hyperkeratosis shows retained nuclei as a sign of delayed maturation of keratinocytes.

Ichthyosis · Very frequent (99-80%)

An abnormality of the skin characterized the presence of excessive amounts of dry surface scales on the skin resulting from an abnormality of keratinization.

Recurrent respiratory infections · Very frequent (99-80%)

An increased susceptibility to respiratory infections as manifested by a history of recurrent respiratory infections.

Eclabion · Frequent (79-30%)

A turning outward of the lip or lips, that is, eversion of the lips.

Erythroderma · Frequent (79-30%)

An inflammatory exfoliative dermatosis involving nearly all of the surface of the skin. Erythroderma develops suddenly. A patchy erythema may generalize and spread to affect most of the skin. Scaling may appear in 2-6 days and be accompanied by hot, red, dry skin, malaise, and fever.

Limitation of joint mobility · Frequent (79-30%)

A reduction in the freedom of movement of one or more joints.

Cataract · Occasional (29-5%)

A cataract is an opacity or clouding that develops in the crystalline lens of the eye or in its capsule.

Foot polydactyly · Occasional (29-5%)

A kind of polydactyly characterized by the presence of a supernumerary toe or toes.

Hand polydactyly · Occasional (29-5%)

A kind of polydactyly characterized by the presence of a supernumerary finger or fingers.

Malignant hyperthermia · Occasional (29-5%)

Malignant hyperthermia is characterized by a rapid increase in temperature to 39-42 degrees C. Malignant hyperthermia may occur in response to either inhalational anesthetics such as halothane, to muscle relaxants such as succinylcholine, or to exercise.

Other findings in the same source

From: Orphanet

Additional reported features include Self-injurious behavior (Occasional (29-5%)); Sudden cardiac death (Occasional (29-5%)); Dehydration (Occasional (29-5%)); Respiratory insufficiency (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Harlequin ichthyosis is Dermatology, with a dermatologist as the relevant type of clinician. Dermatologist; paediatric services for children as appropriate.

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

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.

• Which features of the skin, hair or nails distinguish the possibilities?
• Would photographs over time help document the changes?
• What should be expected from treatment, and how will irritation or other adverse effects be managed?

Treatment discussions and follow-up

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

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.