Biotinidase deficiency is an inherited metabolic disorder characterized by neurological and cutaneous symptoms. Fortunately, it can be treated and the symptoms prevented by
oral administration of the
vitamin biotin. Using dried blood-soaked filter paper cards,
biotinidase activity was determined in the sera of 225,136 newborns in Brazil. Mutation analysis performed on
DNA from 21 babies with low serum
biotinidase activity confirmed that 3 had profound
biotinidase deficiency (less than 10% of mean normal sera
biotinidase activity), 10 had partial
biotinidase deficiency (10 to 30% of mean normal serum activity), 1 was homozygous for partial
biotinidase deficiency, 4 were heterozygous for either profound or partial deficiency, and 3 were normal. Variability in serum
enzyme activities and discrepancies with mutation analyses were probably due to inappropriate handling and storage of samples sent to the laboratory. Obtaining an appropriate control serum at the same time as that of the suspected child will undoubtedly decrease the false-positive rate (0.09%). Mutation analysis can be used to confirm the genotype of these children. The estimated incidence of
biotinidase deficiency in Brazil is about 1 in 9,000, higher than in most other countries. Screening and treatment of
biotinidase deficiency are effective and warranted. These results strongly suggest that
biotinidase deficiency should be included in the newborn mass screening program of Brazil.