The association of the GSTM1 null genotype with female PEXG patients in the current study is in accordance with the data of a group of Greek patients with multiple sclerosis [42]; using this data we calculated and compared the gender-wise distribution of the null genotypes of GSTT1 and GSTM1 between the Greek controls and patients. The gene discussed is GSTM1; the disease is multiple sclerosis.