In fact, as with very long chain acyl-CoA dehydrogenase deficiency (VLCADD), C4 levels in some individuals, overall homozygous with the c.625 G>A variant, in a second DBS, collected after five days of life, have been reported to fall below the cut-off value [11,12,13]. This evidence concerns the gene C4A and very long chain acyl-CoA dehydrogenase deficiency.