Identification and characterization of mutations in patients with holocarboxylase synthetase deficiency

Holocarboxylase synthetase deficiency (HCS) is introduction an autosomal re cessive disorder characterized by metabolic ketoacidosis, abnormal urine or ganic metabolites, and dermatitis. These symptoms are improved by pharmacol ogical doses of biotin. In this study, we have analyzed seven patients with HCS deficiency found in European and Middle Eastern countries by using rev erse transcription/polymerase chain reaction/single-stranded conformation p olymorphism and a sequencing analysis. Although we had previously reported that two mutations were frequent in Japanese patients, no frequent mutation s were found in the patients analyzed in this study. Seven novel mutations were identified in the cDNA of the patients; these included three missense mutations, two single-base deletions that resulted in a termination codon: a three-base in-frame deletion, and a 68-bp deletion. A new polymorphism C1 121T was also identified in four alleles. A transient expression study demo nstrated that the HCS activities of three missense mutations and one amino acid deletion were 1%-14% that of wild-type cDNA; in contrast, the activiti es of the two single-base deletions followed by a termination codon and Asp 571Asn were nearly undetectable. These data suggest that a variety of mutat ions is responsible for decreasing HCS activity and that the aspartate resi due at amino acid position 571 may be crucial for the catalytic activity of HCS.