In the comparison of genotypic and allelic frequencies of polymorphisms rs10766197 of the CYP2R1 gene and rs10877012 of the CYP27B1 gene between severe progression vs. low progression in MS patients, we observed a similar frequency of the AA genotype for rs10766197 of the CYP2R1 gene (15.4% in severe progression vs. 11.6% in low progression). The gene discussed is CYP27B1; the disease is myeloid sarcoma.