Beta-ketothiolase (BKT) deficiency

Alternative names	alpha-methylacetoacetic aciduria 3-ketothiolase deficiency Mitochondrial acetoacetyl-CoA thiolase deficiency T2 deficiency 3-oxothiolase deficiency 2-methyl-3-hydroxybutyric acidaemia
About the condition	BKT deficiency is an organic acid disorder. It is a hereditary disease that is caused by a missing enzyme needed to convert protein into energy. There is also failure to utilise ketone bodies.
Inheritance	Autosomal recessive
Year screening started in WA	2005
Incidence in Australia	Currently unknown
Enzyme defect	Deficiency of 3-ketothiolase, which converts 2-methylacetoacetyl-CoA to propionyl-CoA and acetyl-CoA.
Symptoms if untreated	Episodic ketoacidosis Nausea and vomiting Intellectual disability Coma and death possible Significant clinical heterogeneity
Metabolites on bloodspot screening	Increased 2-methyl-3-hydroxybutyrylcarnitine and tiglylcarnitine (C5OH and C5:1).
Diagnostic tests	Plasma acylcarnitine profile Urine organic acids ACAT1 gene analysis
Treatment	Low-protein diet Carnitine supplementation Avoidance of fasting IV glucose and bicarbonate during crisis episodes
Screening issues	Not all cases will show biochemical abnormalities on newborn screening.