In order to test the hypothesis that HFA-GlcCer partially compensates the loss of HFA-GalCer in Cgt-/- mice and thereby prevents a more severe phenotype, we generated Cgt-/- mice with an additional deficiency in Fa2h. As shown previously, young Fa2h-/- mice form structural and functional normal myelin [15] and did not show behavioral abnormalities that would indicate myelin deficiency. The gene discussed is UGT8; the disease is hyperinsulinemic hypoglycemia, familial, 4.