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Beta-ketothiolase deficiency

Beta-ketothiolase deficiency



Overview

Beta-ketothiolase deficiency is a rare inherited metabolic disorder that stops the body from properly processing the amino acid isoleucine and ketone bodies. Caused by mutations in the ACAT1 gene, it leads to harmful ketoacidotic crises triggered by fasting or common infections

Symptoms

Signs of a Metabolic Crises

Children with this condition are typically healthy between episodes, but attacks can be triggered by infections, fasting, or high-protein meals. Common signs include:

Severe vomiting and poor appetitee

Extreme lack of energy or sleepiness (lethargy)Trouble breathing or fast breathing (tachypnea)Dehydration

Unusual fruity or sweet-smelling breath/urine

Seizures or convulsionss

Loss of consciousness or coma in severe cases

Long-Term Effects

Most children recover quickly if treated during an attack.Repeated or severe untreated crises can lead to developmental delays or intellectual disability.Symptoms often become less frequent or severe as the child gets older.

Causes

Genetic and Biological Mechanisms

Gene Mutation: Changes or pathogenic variants in the ACAT1 gene stop the body from making a working mitochondrial acetoacetyl-CoA thiolase enzyme.

Impaired Breakdown: The missing or weak enzyme cannot process the amino acid isoleucine or breakdown ketone bodies used for energy.

Toxic Buildup: Unprocessed organic acids and related compounds accumulate in the blood and tissues.Inheritance Pattern

Autosomal Recessive: A child must inherit one faulty gene copy from each parent to develop the disorder.

Carrier Parents: Parents of an affected child are typically asymptomatic carriers possessing one normal and one mutated gene copy.

Common Triggers for Episodes

Fasting: Long periods without food.Infections: Fever or acute illnesses.Dietary Stress: Eating high-protein meals.

Diagnosis

Clinical Suspicion: Evaluated when an infant or young child (typically 5 months to 2 years old) experiences a sudden metabolic crisis with ketoacidosis, vomiting, lethargy, or breathing difficulties, often triggered by a viral illness or fasting.

Urine Organic Acid Analysis (GC-MS): Detects pathognomonic marker metabolites including elevated 2-methyl-3-hydroxybutyrate, 2-methylacetoacetate, and tiglylglycine.

Plasma Acylcarnitine Profile (Tandem Mass Spectrometry): May reveal elevated tiglyl-carnitine (C5:1) or other branched-chain intermediates.

Molecular Genetic Testing: Sequencing of the ACAT1 gene confirms the diagnosis by identifying pathogenic mutations.

Enzyme Assay: Measured in cultured skin fibroblasts if genetic variants are unclear or novel

Treatment

Acute Metabolic Crisis Management

Intravenous glucose: Administer IV dextrose immediately to suppress ketone production, even if blood sugar levels are normal.

Correction of acidosis: Give sodium bicarbonate infusions to treat severe metabolic acidosis.

Hydration and electrolytes: Restore fluid balance and monitor electrolyte levels closely.

Supportive care: Provide mechanical ventilation or intensive monitoring if the patient is unconscious or experiencing severe respiratory distress.

Long-Term Management

Avoid fasting: Eat frequent meals and snacks to prevent the body from breaking down fats for energy.

Dietary adjustments: Restrict dietary protein moderately (limiting isoleucine intake) and strictly avoid high-fat or ketogenic diets.

Carnitine supplements: Use L-carnitine if blood carnitine levels are low.

Sick-day protocols: Increase oral carbohydrate intake or seek immediate medical care for IV intervention at the first sign of fever, vomiting, or infection.

Type of Doctor Department : A metabolic specialist or clinical geneticist

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