Clinical and molecular investigation of 37 Japanese patients with multiple acyl-CoA dehydrogenase deficiency: p.Y507D in ETFDH, a common Japanese variant, causes a mortal phenotype

Multiple acyl-CoA dehydrogenase deficiency (MADD) is an inherited metabolic disease caused by a defect in electron transfer flavoprotein alpha (ETFA), ETF beta (ETFB), or ETF dehydrogenase (ETFDH), and riboflavin metabolism disorders have recently been reported to present as mimicking MADD. MADD is roughly classified into neonatal (type 1 or 2) and later-onset (type 3) forms. To identify clinicogenetic characteristics in Japan, we investigated 37 Japanese patients with MADD diagnosed from 1997 to 2020. The causes of MADD were ETFDH deficiency in 26 patients, ETFA deficiency in four, ETFB deficiency in six, and riboflavin metabolism disorder in one. All 15 patients with the neonatal-onset type died by 2 years of age, while five of 22 patients with the later-onset form died by 3 years of age. Furthermore, 8 of 15 patients with the later-onset form of ETFDH deficiency treated with riboflavin were riboflavin non-responders. p.Y507D in ETFDH was identified as the most common variant (9 of 48 alleles, 18.8%). Of two patients with a homozygous p.Y507D variant, one experienced disease onset and died in the neonatal period, while the other experienced disease onset at two months of age and died at two years old, suggesting that the p.Y507D variant results in fatal outcomes. Our study concluded that more than half of Japanese patients with MADD died by three years old, and more than half of patients with the later-onset form had poor responsiveness to riboflavin, partly due to the unique Japanese p.Y507D variant in ETFDH.