Along this line, several ACAD9 mutations are associated to CID (Haack et al., 2010; Rodenburg, 2016) and indeed, stabilization of ACAD9 might represent a therapeutic approach for treating CID, as shown by a riboflavin treatment (the central component of FAD cofactors) where CI activity increased and clinical conditions of ACAD9-defective patients improved (Gerards et al., 2011). This evidence concerns the gene ACAD9 and combined immunodeficiency.