Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency is a rare condition that prevents the body from converting certain fats to energy, particularly during periods without food (fasting).

Signs and symptoms of LCHAD deficiency typically appear during infancy or early childhood. Many affected infants have feeding difficulties, such as an extreme dislike of certain foods or of eating at all (food or feeding aversion), nausea, and vomiting. Other signs and symptoms include lack of energy (lethargy), low blood glucose (hypoglycemia), weak muscle tone (hypotonia), delayed development of milestones, liver problems, and abnormalities in the light-sensitive tissue at the back of the eye (retina). Affected individuals can have impaired vision or difficulty seeing things far away (myopia) or in low light (night blindness). These vision problems worsen over time. Later in childhood, people with this condition may experience muscle pain, breakdown of muscle tissue (rhabdomyolysis), and a loss of sensation in their arms and legs (peripheral neuropathy). Infants and children with LCHAD deficiency are also at risk of serious heart problems, such as a weakened heart (cardiomyopathy) and heart failure; breathing difficulties; coma; and sudden death.

Problems related to LCHAD deficiency can be triggered when the body is under stress, for example during periods of fasting, illnesses such as viral infections, or weather extremes. This disorder is sometimes mistaken for Reye syndrome, a severe disorder that may develop in children while they appear to be recovering from viral infections such as chicken pox or flu. Most cases of Reye syndrome are associated with the use of aspirin during these viral infections.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Variants (also known as mutations) in the HADHA gene cause LCHAD deficiency. The HADHA gene provides instructions for making part of an enzyme complex called mitochondrial trifunctional protein. This enzyme complex functions in mitochondria, the energy-producing centers within cells. As the name suggests, mitochondrial trifunctional protein contains three enzymes that each perform a different function. This enzyme complex is required to break down (metabolize) a group of fats called long-chain fatty acids. Long-chain fatty acids are found in foods such as milk and certain oils. These fatty acids are stored in the body's fat tissues. Fatty acids are a major source of energy for the heart and muscles. During periods of fasting, fatty acids are also an important energy source for the liver and other tissues.

Variants in the HADHA gene that cause LCHAD deficiency disrupt one of the functions of this enzyme complex. These variants prevent the normal processing of long-chain fatty acids from food and body fat. As a result, these fatty acids are not converted to energy, which can lead to some features of this disorder, such as lethargy and hypoglycemia. Long-chain fatty acids or partially metabolized fatty acids may also build up and damage the liver, heart, muscles, and retina. This abnormal buildup causes the other signs and symptoms of LCHAD deficiency.

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

The incidence of LCHAD deficiency is unknown. One estimate, based on a Finnish population, indicates that 1 in 62,000 pregnancies is affected by this disorder. In the United States, the incidence is probably much lower.

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.

Hypoglycemia · Very frequent (99-80%)

A decreased concentration of glucose in the blood.

Hypoketotic hypoglycemia · Very frequent (99-80%)

A decreased concentration of glucose in the blood associated with a reduced concentration of ketone bodies.

Photophobia · Very frequent (99-80%)

Excessive sensitivity to light with the sensation of discomfort or pain in the eyes due to exposure to bright light.

Abnormal electroretinogram · Frequent (79-30%)

Any abnormality of the electrical responses of various cell types in the retina as measured by electroretinography.

Exotropia · Frequent (79-30%)

A form of strabismus with one or both eyes deviated outward.

Global developmental delay · Frequent (79-30%)

A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.

Hepatomegaly · Frequent (79-30%)

Abnormally increased size of the liver.

Hypertrophic cardiomyopathy · Frequent (79-30%)

Hypertrophic cardiomyopathy (HCM) is defined by the presence of increased ventricular wall thickness or mass in the absence of loading conditions (hypertension, valve disease) sufficient to cause the observed abnormality.

Other findings in the same source

From: Orphanet

Additional reported features include Hypotonia (Frequent (79-30%)); Peripheral neuropathy (Frequent (79-30%)); Visual loss (Frequent (79-30%)); Abnormality of metabolism/homeostasis (Frequent (79-30%)); Abnormality of retinal pigmentation (Occasional (29-5%)); Chorioretinal abnormality (Occasional (29-5%)); Chorioretinal atrophy (Occasional (29-5%)); Failure to thrive (Occasional (29-5%)); Feeding difficulties (Occasional (29-5%)); Generalized hypotonia (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 Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency is Metabolic Medicine, with a metabolic specialist / clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with metabolic specialist / clinical geneticist referral.

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.

• Is a biochemical or molecular result needed to clarify the diagnosis?
• Does this condition require an individual plan for illness or reduced food intake?
• Should nutrition advice come from a specialist metabolic dietitian?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency. 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.

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.