This notwithstanding, successes have now been reported for cases involving metachromatic leukodystrophy (in which patients are deficient in arylsulfatase A [ARSA], leading to the accumulation of sulfatide in myelin-producing cells that produce severe cognitive and motor damage), aromatic l-amino acid decarboxylase (AADC) deficiency, and adrenoleukodystrophy (ALD, with mutated ABCD1 gene, affecting the adrenal cortex). Here, ARSA is linked to metachromatic leukodystrophy.