Metachromatic leukodystrophy is due to lack of arylsulfatase A, resulting in accumulation of the sphingolipid sulfatide, while Krabbe disease is caused by deficiency in galactosylceramidase, with consequent accumulation of galactosylceramide and galactosylsphingosine (psychosine) (Figure 1). Here, GALC is linked to Krabbe disease.