Multigenic basis for maple syrup urine disease with emphasis on mutations in branched chain dihydrolipoyl acyltransferase

Danner, Dean J.; McKean, Martha C.

doi:10.1007/978-3-0348-8981-0_19

Cited by 1 publication

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“…Subsequently, we reported that defect(s) in the E1 component are also responsible for this disease (Indo et al 1987). Molecular defects in the BCKDH have been characterized in the classical, intermediate, and thiamine-responsive phenotypes (Chuang and Shih 1995;Indo and Matsuda 1996;Danner and McKean 1996). The classical phenotype is caused by mutation of any of the E1α (Zhang et al 1989;Matsuda et al 1990;Fisher et al 1991a), E1 , or E2 genes Herring et al 1992).…”

Section: Introductionmentioning

confidence: 99%

Molecular basis of intermittent maple syrup urine disease: novel mutations in the E2 gene of the branched-chain α-keto acid dehydrogenase complex

et al. 1998

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The E2 gene of the branched-chain α-keto acid dehydrogenase (BCKDH) complex was studied at the molecular level in three patients with intermittent maple syrup urine disease (MSUD). All three patients had higher BCKDH activity than did those with the classical phenotype. In the first patient, a single base substitution from A to G in intron 8 created a new 5Ј splice site and caused an insertion of 126 nucleotides between exons 8 and 9 by activating an upstream cryptic 3Ј splice site in the same intron. The predicted mRNA encoded a truncated protein with 282 amino acids including 4 novel ones at the carboxyl terminus, compared with the normal protein with 421 amino acids. In vitro, the region from the patient but not from a normal control was recognized and was recovered as a novel exon, indicating that the single substitution was responsible for incorporation of the region into mRNA. This mutation probably supports an exon definition model in which the spliceosome recognizes a 3Ј splice site and then scans downstream for an acceptable 5Ј splice site, thereby defining an exon. The second patient was homozygous for a G to T transversion at nucleotide 1463 in exon 11, which predicted a substitution of the termination codon by a leucine residue and the addition of 7 extra amino acids at the carboxyl terminus. For each mutation, these two patients were homozygous and their parents were heterozygous. The third patient was a compound heterozygote for a C to G transversion at nucleotide 309 in exon 4 and a G to A transition at nucleotide 1165 in exon 9, causing an Ile-toMet substitution at amino acid 37 and a Gly-to-Ser substitution at amino acid 323, respectively. Taken together, these results indicate that the molecular basis of intermittent phenotype MSUD in some patients can be due to mutations in the E2 gene, giving rise to a low but significant residual activity of the BCKDH complex.

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