ETFDH genetic analysis may identify pathogenic variants but several reports in the literature describe MADD patients carrying only a single heterozygous variant or even with no evidence of variants in either ETFDH, ETFA, and ETFB genes but with a suggestive MADD diagnosis supported by the clinical history, acylcarnitine profile, and response to therapy. The gene discussed is ETFB; the disease is multiple acyl-CoA dehydrogenase deficiency.