Holocarboxylase synthetase (HLCS) deficiency is an autosomal recessive disorder of biotin metabolism that results from holocarboxylase synthetase activity disruption. HLCS deficiency is also called multiple carboxylase deficiency, because deficient HLCS activity results in reduced activity of multiple carboxylases. In humans, four carboxylases are known to be biotinylated by HLCS. They are pyruvate carboxylase, propionyl-CoA carboxylase, methylcrotonyl-CoA carboxylase, and acetyl-CoA carboxylase. Symptoms of HLCS deficiency include metabolic acidosis, a characteristic organic aciduria, lethargy, hypotonia, convulsions, and dermatitis.
