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.

IntroduçãoA tirosina é um aminoácido não-essencial, proveniente da dieta, da hidroxilação da fenilalanina ou do catabolismo protéico 1 e pode ter duas diferentes rotas metabóli-cas: a sua conversão a aminas biológicas através de várias etapas catalisadas por enzimas específicas 2,3 ou a sua oxidação no ciclo dos ácidos tricarboxílicos a CO 2 e H 2 O 2,3,4 . A tirosinemia neonatal transitória (TNT) é devi- AbstractObjective: To evaluate the frequency of transient neonatal tyrosinemia, with or without secondary hyperphenylalaninemia, observed through neonatal screening for metabolic disorders, and the need of monitoration and intervention with drugs and/or special diet in selected cases.Methods: 457.870 dried blood samples obtained by heel stick from 3 to 20 days old babies were qualitatively evaluated by amino acid thin-layer chromatography. Positive cases were quantitatively confirmed in serum samples by fluorimetric measurement of tyrosine and phenylalanine.Results: 1.231 dried blood samples displayed positive results for tyrosine in the cromatographic evaluation. The fluorimetric serum analysis disclosed normal levels of tyrosine and phenylalanine in 822 patients. The remained 409 patients showed high tyrosine levels and were placed in three groups according to the tyrosine concentration. In 118 of these cases serum phenylalanine was also increased.Conclusions: Transient neonatal tyrosinemia is a very frequent disorder in neonates (1/372); in some cases very high levels were found, not only of tyrosine but also phenylalanine. As this finding is not yet accepted as absolutely harmless, the monitoration of this situation and the use of measures to lower the tyrosine and phenylalanine levels should be considered by the pediatrician. J. pediatr. (Rio J.). 1998; 74(6):447-450: tyrosinemia, inborn error of metabolism, amino acid disorders, neonatal screening. ResumoObjetivos: Avaliar a freqüência da tirosinemia neonatal transitória, com ou sem hiperfenilalaninemia secundária, observada através da triagem neonatal para erros inatos do metabolismo ("teste do pezinho"), e a necessidade de monitoramento e eventual intervenção medicamentosa e/ou dietética em casos específicos.Métodos: Foram analisadas 457.870 amostras de sangue seco obtido por punção de calcâneo de crianças de 3 a 20 dias de vida, através de cromatografia qualitativa de aminoácidos em camada delgada. Os casos positivos foram confirmados quantitativamente em amostras séricas pelas dosagens fluorimétricas da tirosina e da fenilalanina.Resultados: 1.231 amostras de sangue seco impregnado em papel filtro apresentaram resultados positivos para tirosina na avaliação cromatográfica. A análise sérica por método fluorimétrico revelou valores normais de tirosina e fenilalanina em 822 pacientes; os restantes 409 apresentaram tirosina elevada e foram divididos em três grupos de acordo com a concentração de tirosina observada. Em 118 destes pacientes foram observados também níveis de fenilalanina superiores ao limite de referência.Conclusões: A tirosinemia neonatal t...