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Background: Maple syrup urine disease (MSUD) is an autosomal recessive inherited metabolic disorder caused by the deficient activity of the branched-chain α-keto acid dehydrogenase (BCKD) enzymatic complex. BCKD is a mitochondrial complex encoded by four genes: BCKDHA, BCKDHB, DBT, and DLD. MSUD is predominantly caused by mutations in the BCKDHA, BCKDHB, and DBT genes which encode the E1α, E1β, and E2 subunits of the BCKD complex, respectively. The aim of this study was to characterize the genetic basis of MSUD in a cohort of Chilean MSUD patients by identifying point mutations in the BCKDHA, BCKDHB, and DBT genes and to describe their impact on the phenotypic heterogeneity of these patients. This manuscript describes a cross-sectional study of 18 MSUD patients carried out using PCR and DNA sequencing.Results: Four novel pathogenic mutations were identified: one in BCKDHA (p.Thr338Ile), two in BCKDHB (p.Gly336Ser e p.Pro240Thr), and one in DBT (p.Gly406Asp). Four additional pathogenic mutations found in this study have been described previously.Conclusion: There were no correlations between the genotype and phenotype of the patients. Thus, if MSUD is diagnosed earlier, with a neonatal screening approach, it might be possible to establish genotype-phenotype relationships more efficiently.

CO 2 que forneça um teste respiratório "positivo" para detecção da galactosemia de maior sensibilidade e especificidade. As crianças doentes tiveram uma % acumulativa de 13 C no ar expirado proveniente da galactose marcada (CUMPCD) variando em média de 0,03% no tempo de 30 minutos a 1,67% no tempo de 120minutos. Em contrapartida, os indivíduos saudáveis apresentaram enriquecimentos e uma CUMPCD maiores, com valores de 0,4% no tempo de 30 minutos a 5,58% no tempo 120 minutos.Portanto, nesse estudo ficou evidente que há uma diferença marcante na oxidação da galactose em crianças com e sem galactosemia, logo teste respiratório é útil em discriminar crianças com deficiência na GALT. Palavras-Chave: Galactosêmicas. Marcação por isótopos. Oxidação.Criança.

Background: Maple syrup urine disease (MSUD) is an autosomal recessive inherited metabolic disease caused by deficient activity of the branched-chain α-keto acid dehydrogenase (BCKD) enzymatic complex. BCKD is a mitochondrial complex encoded by four genes: BCKDHA, BCKDHB, DBT, and DLD. MSUD is predominantly caused by mutations in the BCKDHA, BCKDHB, and DBT genes encoding the E1α, E1β, and E2 subunits of the BCKD complex, respectively. The aim of this study was to characterize the genetic basis of MSUD by identifying point mutations in the BCKDHA, BCKDHB, and DBT genes in a cohort of Chilean MSUD patients, and to describe their phenotypic heterogeneity. It is a descriptive cross-sectional study with 18 MSUD patients was carried out using PCR and DNA sequencing. Results: Four new pathogenic mutations were identified in the 18 patients that were analyzed: one in BCKDHA (p.Thr338Ile); two in BCKDHB (p.Gly336Ser e p.Pro240Thr); and one in DBT (p.Gly406Asp). Four additional pathogenic mutations found in the analyzed patients have been described previously. Conclusion: There were no correlations observed between genotypes and phenotypes. Thus, if MSUD is diagnosed more promptly, such as in neonatal screening, it might be possible to establish genotype-phenotype relationships more efficiently. Keywords: inborn errors of metabolism; maple syrup urine disease; branched-chain amino acids; valine; leucine; isoleucine.