J. Inher. Metab. Dis. t4 (1991) 400-402 © SSIEM and KluwerAcademicPublishers. Printed in the Netherlands Short Communication Seven-Year Experience of a Reference Laboratory for Detection of Inborn Errors of Metabolism in Brazil R. GIUGLIANI, J. C. DUTRA, M. L. BARTH, C. S. DUTRA-FILHO, S. L. GOLDENFUM and M. WAJNER Medical Genetic Unit, Clinical Hospital of Porto Alegre, Rua Ramiro Barcelos 2350, Porto Alegre RS 90210, Brazil Inborn errors of metabolism (IEM) are a heterogeneous group of more than 300 genetic defects related to the synthesis, metabolism, transport and storage of biochemical compounds. The large number of specific biochemical techniques required for their detection and diagnosis and the rarity of each disorder makes advisable the creation of regional reference diagnostic laboratories. We now present the results of our investigations performed in high risk patients at the Regional Laboratory for Inborn Errors of Metabolism, Porto Alegre, Brazil, during a 7-year period. MATERIALS AND METHODS We studied 3749 patients referred to our laboratory from 1982 to 1989. The main clinical indications for referral were: neuromotor delay/mental retardation (1088), seizures (489) and hepatomegaly and/or splenomegaly (196). All patients were initially submitted to screening tests consisting of qualitative tests on urine (Benedict's, ferric chloride, dinitrophenylhydrazine, nitrosonaphthol, cyanide-nitroprusside, toluidine blue, acetyl-trimethylammonium chloride, p-nitroaniline, and Ehrlich tests) and paper amino acid chromatography of blood and urine. When at least one test showed a positive or doubtful result, the patient was recalled and the investigation continued through more specific methods, consisting of chromatographic analysis of urine (glycosaminoglycans, oligosaccharides, sialyloligosaccharides and carbohydrates) and quantitative and/or qualitative assays of urine and/or blood metabolites (oxalic acid, sialic acid, glycosaminoglycans, porphobilinogen, amino acids and organic acids). If there was a suspicion of an IEM undetectable by the screening tests based on clinical, radiological and/or laboratory notes, the patient was then submitted to a focussed investigation through specific diagnostic methods. RESULTS Investigations have been completed on 3161 patients so far, and a metabolic defect was identified in 251 cases (7.9%) (Table 1). The most frequently diagnosed 40O