Maple syrup disease (MSUD) is a rare autosomal recessive disorder caused primarily by mutations of branched-chain keto acid dehydrogenase complex (BCKDC). BCKDC includes at least four pathogenic genes of BCKDHA, BCKDHB, DLD and DBT. The clinical manifestations of MSUD are complex, and the main symptoms at the early stage include difficulty in feeding, drowsiness, change in muscle tone and special urine flavor of maple syrup. As the disease progresses, convulsion, hypoglycemia, coma and systemic failure may occur. MSUD is easily missed or misdiagnosed during the neonatal period. This paper provides a review for recent progress made in research on MSUD including etiology, physiopathology, clinical manifestation, auxiliary examination and treatment, with a particular emphasis on genetic testing and treatment.
3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) ; genetics ; Humans ; Maple Syrup Urine Disease ; diagnosis ; genetics ; therapy ; Mutation

OBJECTIVETo investigate the clinical features of one pair of twin neonates with maple syrup urine disease (MSUD) in the Chinese Han population and pathogenic mutations in related genes, and to provide guidance for the early diagnosis and treatment of MSUD.

METHODSThe clinical and imaging data of the twin neonates were collected. The peripheral blood samples were collected from the twin neonates and their parents to detect the genes related to MSUD (BCKDHA, BCKDHB, DBT, and DLD). The loci with gene mutations were identified, and a bioinformatic analysis was performed.

RESULTSTwo mutations were detected in the BCKDHB gene, missense mutation c.304G>A (p.Gly102Arg) and nonsense mutation c.331C>T (p.Arg111*), and both of them were heterozygotes. The mutation c.304G>A (p.Gly102Arg) had not been reported in the world. Their father carried the missense mutation c.304G>A (p.Gly102Arg), and their mother carried the nonsense mutation c.331C>T (p.Arg111*).

CONCLUSIONSThe c.331C>T (p.Arg111*) heterozygous mutation in BCKDHB gene is the pathogenic mutation in these twin neonates and provides a genetic and molecular basis for the clinical features of children with MSUD.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) ; genetics ; Diseases in Twins ; Female ; Humans ; Infant, Newborn ; Male ; Maple Syrup Urine Disease ; genetics ; Mutation

In this study, Streptomyces avermitilis Bjbm0006 which produces four avermectin B components was used as an original test strain. A replacement plasmid containing a gene cluster bkdAB (branched-chain alpha-keto acid dehydrogenase gene) involved in the biosynthesis of avermectin B in S. avermitilis Bjbm0006 was constructed by means of PCR technique and then named as pHJ5821 (pHZ1358::bkdAB&erm). A recombinant strain Bjbm5821 was obtained after the gene cluster was interrupted by double crossover. This strain was tested in laboratory conditions and analysed by PCR using the total DNA as template. The HPLC analysis showed that the strain Bjbm5821 synthesized the same 'a' components Bla and B2a as the original strain did. However, It lost the ability for the production of 'b'components for example B1b and B2b. A novel compound was detected in fermentation products. The results of present study suggests that the production of gene cluster bkdAB may play a main role similar to alpha-ketoisovaleric acid dehydrogenase in the pathway of avermectin synthesis.
3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) ; genetics ; Ivermectin ; analogs & derivatives ; metabolism ; Recombinant Proteins ; biosynthesis ; genetics ; Streptomyces ; enzymology ; genetics

Maple syrup urine disease (MSUD) is an autosomal recessive disorder. Impaired activity of the branched-chain 2-oxo acid dehydrogenase complex causes accumulation of branched-chain L-amino and 2-oxo acid that can exert neurotoxic effects. MSUD presents heterogeneous clinical and molecular phenotypes. Severity of the disease, ranging from classical to mild variant types, is commonly classified on the basis of indirect parameters, e.g. onset, leucine tolerance and/or residual enzyme activity in cell. Since early 1990's, tandem mass spectrometry has been applied to newborn screening, because it is amenable to population-wide testing for a large number of disorders of fatty acid, organic acid, and amino acid metabolism. And so, we report a case of MSUD in 15 days old boy detected by newborn screening using tandem mass spectrometry.
3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) ; Acer* ; Humans ; Infant, Newborn* ; Leucine ; Male ; Maple Syrup Urine Disease* ; Mass Screening* ; Metabolism ; Phenotype ; Tandem Mass Spectrometry*

Maple syrup urine disease (MSUD) is a disorder that involves the metabolism of branched chain amino acids, arising from a defect in branched-chain alpha-keto acid dehydrogenase complex. Mutations have been identified in the BCKDHA, BCKDHB, or DBT genes, which encode different subunits of the BCKDH complex. Although encephalopathy and progressive neurodegeneration are its major manifestations, the severity of the disease may range from the severe classic type to milder intermediate variants. We report two Korean siblings with the milder intermediate MSUD who were diagnosed with MSUD by a combination of newborn screening tests using tandem mass spectrometry and family genetic screening for MSUD. At diagnosis, the patients' plasma levels were elevated for leucine, isoleucine, valine, and alloisoleucine, and branched-chain alpha-keto acids and branched-chain alpha-hydroxy acids were detected in their urine. BCKDHA, BCKDHB, and DBT analysis was performed, and two novel mutations were identified in BCKDHB. Our patients were thought to have the milder intermediate variant of MSUD, rather than the classic form. Although MSUD is a typical metabolic disease with poor prognosis, better outcomes can be expected if early diagnosis and prompt management are provided, particularly for milder forms of the disease.
3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) ; Amino Acids ; Diagnosis ; Early Diagnosis ; Genetic Testing ; Humans ; Infant, Newborn ; Isoleucine ; Leucine ; Maple Syrup Urine Disease* ; Mass Screening ; Metabolic Diseases ; Metabolism ; Plasma ; Prognosis ; Siblings* ; Tandem Mass Spectrometry ; Valine

OBJECTIVEMaple syrup urine disease (MSUD) is an autosomal recessive metabolic disorder that is caused by mutations in the subunits of the branched chain α-ketoacid dehydrogenase (BCKD) complex. This report presents a Han ethnic Chinese newborn infant with the severe classic form of MSUD caused by two novel missense mutations in the BCKDHB gene.

METHODThe clinical and biochemical data of a Chinese neonate with classic form of MSUD were analyzed, and the DNA sequences of BCKDHA, BCKDHB, DBT and DLD genes were investigated for mutations. Then the DNA samples of the proband and the patient's parents were tested with Sanger sequencing.

RESULTThe manifestations of this patient were poor feeding, low reaction, and compensatory metabolic acidosis. Tandem mass spectrometry (MS/MS) showed that leucine and valine were significantly higher than normal. Urine gas chromatography-mass spectrometry (GC/MS) showed significant abnormality. Brain CT scan showed white matter changes. We identified two previously unreported mutations in the BCKDHB gene, p.Leu194Phe (c.580 C>T) and p.Ser199Arg (c.597 T>G) in exon 5. Segregation analysis showed that the novel mutation p.Ser199Arg was maternally inherited and the novel mutation p.Leu194Phe was paternally inherited. Neither mutation was found in the 186 alleles of 93 normal Han ethnic Chinese individuals. In human BCKDHB protein crystal structure, the 194th and 199th amino acids changes are likely to affect the spatial structure of the protein. The 194th and 199th amino acid of human BCKDHB protein was conserved among species. PolyPhen protein function prediction indicated that the 194th and 199th amino acid changes were likely to affect protein function.

CONCLUSIONTwo novel missense mutations were identified in the BCKDHB gene in the Chinese patient with MSUD.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) ; genetics ; Alleles ; Asian Continental Ancestry Group ; Base Sequence ; DNA ; Exons ; Gas Chromatography-Mass Spectrometry ; Humans ; Infant ; Infant, Newborn ; Maple Syrup Urine Disease ; genetics ; Mutation, Missense ; Tandem Mass Spectrometry