Multiple carboxylase deficiency (MCD) is a term used to describe inborn errors of biotin metabolism characterized by reduced activities of biotin-dependent enzymes resulting in a wide spectrum of symptoms, including feeding difficulty, breathing difficulties, lethargy, seizures, skin rash, alopecia, and developmental delay. The prevalence of MCD is unknown, but the condition is rare. There is no specific geographic or ethnic predominance. There are two major clinical forms of MCD depending on their underlying cause: biotinidase deficiency (see this term) in which affected individuals typically develop symptoms of variable severity during the first few months of life, and holocarboxylase synthetase deficiency (see this term) in which affected individuals usually develop symptoms within hours, days or weeks of birth. Biotinidase deficiency is caused by mutations in the BTD gene (3p25) and holocarboxylase synthetase deficiency by mutations in the HLCS gene (21q22.1). Both disorders are inherited as autosomal recessive traits.
Last update: July 2011