Muscle biopsy (Oil Red O staining) and acylcarnitine profile (elevated C5‐C18 acylcarnitines) findings suggested MADD, which was confirmed by genetic analysis showing biallelic variants in the ETFDH gene (c.1763A>G, p.(His588Arg); c.897G>A, p.(Leu299=)). Here, ETFDH is linked to multiple acyl-CoA dehydrogenase deficiency.