ETFDH and multiple acyl-CoA dehydrogenase deficiency: Of the initially screened 3638 studies, 30 met the inclusion criteria, including 498 late-onset MADD patients with biallelic variations and 62 with single heterozygous variations in ETFDH. The relative frequency of patients carrying null variants was lower in the biallelic group (21%, 95% CI [16%-27%]) than that in the heterozygous group (34%, 95% CI [23%-48%]) (P = 0.044).