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Identification of two mutations in a compound heterozygous child with dihydrolipoamide dehydrogenase deficiency
Y S Hong1, D S Kerr, W J Craigen
1Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York at Buffalo 14214, USA.
Insights
Dihydrolipoamide dehydrogenase (E3) deficiency in an infant was caused by two novel mutations. These genetic defects, identified through DNA sequencing, led to reduced E3 enzyme activity and protein levels, impacting metabolism.
Area of Science:
- Biochemistry
- Genetics
- Metabolic Disorders
Background:
- Dihydrolipoamide dehydrogenase (E3) is a crucial enzyme in the pyruvate dehydrogenase complex, essential for cellular energy metabolism.
- Deficiency in E3 activity can lead to severe metabolic disturbances, including lactic acidosis and neurological dysfunction.
Abstract:
An infant girl with elevated blood lactate, pyruvate, and plasma branched-chain amino acids was diagnosed with dihydrolipoamide dehydrogenase (E3; dihydrolipoamide: NAD+ oxidoreductase, EC 1.8.1.4) deficiency. Activities of the pyruvate dehydrogenase complex and E3 from patient were 26 and 2% of controls in blood lymphocytes, and 11 and 14% in cultured skin fibroblasts, respectively. Western blot analysis demonstrated that the amount of E3 protein in fibroblasts from the patient and her father was about half of controls, while Northern blot analysis showed normal amounts of E3 RNA. DNA sequencing of cloned full-length E3 cDNAs from the patient revealed two mutations in separate alleles. One is a single base insertion of an extra adenine in the last codon of the leader peptide sequence (TAC-->TAAC) leading to a nonsense mutation which results in the premature termination of the precursor E3 polypeptide (Y35X). The other is a missense mutation due to substitution of guanine for adenine, causing an Arg-->Gly substitution at amino acid 460 of the mature protein (R460G) which triggers the loss of E3 activity probably by structural change in the E3 dimer. DNA sequencing of E3 cDNAs from the parents demonstrated that the nonsense mutation was inherited from the father and the missense mutation was inherited from the mother.