A combined genotype of polymorphisms of methionine metabolism has been associated with CNS demyelination in methotrexate-treated patients. Within a sample of 86 patients with X-linked adrenoleukodystrophy, this genotype was overrepresented in a subgroup of 15 patients with adrenomyeloneuropathy (AMN) with CNS demyelination (adrenoleukomyeloneuropathy) in comparison to 49 AMN patients without CNS demyelination ("pure" AMN; p = 0.002), suggesting that methionine metabolism might contribute to the phenotypic variability in adrenoleukodystrophy.