Genetic variants of methionine metabolism and X-ALD phenotype generation: results of a new study sample.
X-linked adrenoleukodystrophy (X-ALD) is the most common inherited leukodystrophy. Nevertheless, no genotype-phenotype correlation has been established so far. Unidentified modifier genes or other cofactors are suspected to modulate phenotype and prognosis. We recently described polymorphisms of methionine metabolism as possible disease modifiers in X-ALD. To retest these findings, we analyzed 172 new DNA samples of X-ALD patients from different populations (France, Germany, USA, China) by genotyping eight genetic variants of methionine metabolism, including DHFR c.594+59del19bp, CBS c.844_855ins68, MTR c.2756A>G, MTHFR c.677C>T and c.1298A>C, MTRR c.60A>G, RFC1 c.80G>A, and Tc2 c.776C>G. We compared three X-ALD phenotypes: childhood-onset cerebral demyelinating inflammatory type (CCALD; n = 82), adulthood onset with focal cerebral demyelination (ACALD; n = 38), and adulthood onset without cerebral demyelination (AMN; n = 52). The association of genotypes and phenotypes was analyzed with univariate two-sided Pearson's chi(2). In the comparison between AMN and CCALD, the G allele of Tc2 c.776C>G was associated with X-ALD phenotypes (chi(2) = 6.1; P = 0.048). The prevalence of the GG genotype of Tc2 c.776C>G was higher in patients with CNS demyelination compared to those without CNS demyelination (chi(2) = 4.42; P = 0.036). The GG genotype was also more frequent in CCALD compared to AMN (chi(2) = 4.7; P = 0.031). The other polymorphisms did not show any significant associations in this study sample. Whereas the influence of other polymorphisms of methionine metabolism was not confirmed, the present study supports the previously made observation that the Tc2 genotype contributes to X-ALD phenotype generation.