Beta-ketothiolase deficiency

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Beta-ketothiolase deficiency is an inherited disorder in which the body cannot effectively process a protein building block (amino acid) called isoleucine. This disorder also impairs the body's ability to process ketones, which are molecules produced during the breakdown of fats.

The signs and symptoms of beta-ketothiolase deficiency typically appear between the ages of 6 months and 24 months. Affected children experience episodes of vomiting, dehydration, difficulty breathing, extreme tiredness (lethargy), and, occasionally, seizures. These episodes, which are called ketoacidotic attacks, sometimes lead to coma. Ketoacidotic attacks are frequently triggered by infections or periods without food (fasting), and increased intake of protein-rich foods can also play a role.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the ACAT1 gene cause beta-ketothiolase deficiency. This gene provides instructions for making an enzyme that is found in the energy-producing centers within cells (mitochondria). This enzyme plays an essential role in breaking down proteins and fats from the diet. Specifically, the ACAT1 enzyme helps process isoleucine, which is a building block of many proteins, and ketones, which are produced during the breakdown of fats.

Mutations in the ACAT1 gene reduce or eliminate the activity of the ACAT1 enzyme. A shortage of this enzyme prevents the body from processing proteins and fats properly. As a result, related compounds can build up to toxic levels in the blood. These substances may cause the blood to become too acidic (ketoacidosis) and can damage the body's tissues and organs, particularly in the nervous system.

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 mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Beta-ketothiolase deficiency appears to be very rare. Fewer than 250 affected individuals have been reported in the medical literature.

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 higher mental function · Very frequent (99-80%)

Cognitive, psychiatric, or memory anomaly.

Acidosis · Very frequent (99-80%)

Abnormal acid accumulation or depletion of base.

Fever · Very frequent (99-80%)

Body temperature elevated above the normal range.

Hyperuricemia · Very frequent (99-80%)

The concentration of uric acid in the blood circulation is above the upper limit of normal.

Ketonuria · Very frequent (99-80%)

High levels of ketone bodies (acetoacetic acid, beta-hydroxybutyric acid, and acetone) in the urine. Ketone bodies are insignificant in the blood and urine of normal individuals in the postprandial or overnight-fasted state.

Metabolic acidosis · Very frequent (99-80%)

Metabolic acidosis (MA) is characterized by a fall in blood pH due to a reduction of serum bicarbonate concentration. This can occur as a result of either the accumulation of acids (high anion gap MA) or the loss of bicarbonate from the gastrointestinal tract or the kidney (hyperchloremic MA). By definition, MA is not due to a respirary cause.

Tachypnea · Very frequent (99-80%)

Very rapid breathing.

Vomiting · Very frequent (99-80%)

Forceful ejection of the contents of the stomach through the mouth by means of a series of involuntary spasmic contractions.

Apathy · Frequent (79-30%)

Apathy is a quantitative reduction of interest, motivation and the initiation and persistence of goal-directed behavior, where often the accompanying emotions, thoughts, and social interactions are also diminished. The individual is typically non-reactive to provocations, positive or negative, and appears to not care. Distinguished from lethargy which involves lack of physical or mental energy.

Coma · Frequent (79-30%)

The complete absence of wakefulness and consciousness, which is evident through a lack of response to any form of external stimuli.

Cough · Frequent (79-30%)

A sudden, audible expulsion of air from the lungs through a partially closed glottis, preceded by inhalation.

Diarrhea · Frequent (79-30%)

Abnormally increased frequency (usually defined as three or more) loose or watery bowel movements a day.

Excessive daytime somnolence · Frequent (79-30%)

A state of abnormally strong desire for sleep during the daytime.

Hyperammonemia · Frequent (79-30%)

An increased concentration of ammonia in the blood.

Other findings in the same source

From: Orphanet

Additional reported features include Increased total leukocyte count (Frequent (79-30%)); Ketoacidosis (Frequent (79-30%)); Reduced consciousness (Frequent (79-30%)); Thrombocytosis (Frequent (79-30%)); Dehydration (Frequent (79-30%)); Abnormal metabolic brain imaging by MRS (Occasional (29-5%)); Agitation (Occasional (29-5%)); Anorexia (Occasional (29-5%)); Ataxia (Occasional (29-5%)); Body odor (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 Beta-ketothiolase 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 Beta-ketothiolase 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.

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.