Pyruvate carboxylase (PC) deficiency is a rare inborn error of metabolism. Three clinical presentations have been reported. An infantile form (Type A) is characterized by onset between two and five months of age with lactic acidemia and delayed mental and motor development, failure to thrive, pyramidal tract signs, ataxia, nystagmus, convulsions and often death in infancy or early childhood. This form has been seen primarily in North American Indians. A neonatal form (Type B), first described in France though occurring worldwide, is characterized by severe lactic acidosis, anorexia, lethargy, hypotonia, hepatomegaly, convulsions, pyramidal tract signs, and severely delayed psychomotor development with the majority of infants dying within the first three months of life. The intermittent or benign form (Type C) has only been reported in a few cases, and is characterized by normal or mildly delayed neurological development and episodes of metabolic acidosis. Intermediate cases of moderate-severe PC deficiency have also been described that do not fit into one of these three categories, including cases of somatic mosaicism. PC deficiency is reported to have an approximate incidence in most populations of 1 in 250,000 births. In native North American Ojibwa, Cree and Micmac tribes of the Algonquin-speaking peoples the carrier frequency may be as high as 1 in 10.