Molecular basis of intermittent maple syrup urine

Authors: Motoko Tsuruta Hiroshi Mitsubuchi Sek Mardy Yuichi Miura Yumi Hayashida Akihiko Kinugasa Takateru Ishitsu Ichiro Matsuda Yasuhiro Indo

Publish Date: 1998/06

Volume: 43, Issue: 2, Pages: 91-

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Abstract

Thank you for visiting naturecom You are using a browser version with limited support for CSS To obtain the best experience we recommend you use a more up to date browser or turn off compatibility mode in Internet Explorer In the meantime to ensure continued support we are displaying the site without styles and JavaScriptThe E2 gene of the branchedchain αketo 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 5′ splice site and caused an insertion of 126 nucleotides between exons 8 and 9 by activating an upstream cryptic 3′ 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 3′ splice site and then scans downstream for an acceptable 5′ 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 IletoMet substitution at amino acid 37 and a GlytoSer 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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