Background Electron transfer flavoprotein is a mitochondrial matrix protein composed of alpha- and beta-subunits (ETFα and ETFβ, respectively). This protein transfers electrons between several mitochondrial dehydrogenases and the main respiratory chain via ETF dehydrogenase (ETF-DH). Defects in ETF or ETF-DH cause glutaric acidemias type II (GAII).
Materials and methods We investigated the molecular basis of ETFα deficiency in two Japanese children with different clinical phenotypes using expression study.
Results Patient 1 had the severe form of GAII, a compound heterozygote of two mutations: 799G to A (αG267R) and nonsense 7C to T (αR3X). Patient 2 had the mild form and carried two heterozygous mutations: 764G to T (αG255V) and 478delG (frameshift). Both patients had one each of missense mutations in one allele; the others were either nonsense or truncated. Restriction enzyme digestion assay using genomic DNAs from 100 healthy Japanese revealed that these mutations were all novel. No signal for ETFα was detected by immunoblotting in cases of missense mutants, while wild-type cDNA resulted in expression of ETFα protein. Transfection with wild-type ETFα cDNA into cultured cells from both patients elevated incorporation of radioisotope-labelled fatty acids.
Conclusion These four mutations were pathogenic for GAII and missense mutations, αG255V and αG267R were considered anecdotal for mild and severe forms, respectively.