Vitamin D-dependent rickets as a possible risk factor for multiple sclerosis

Background: Vitamin D-dependent rickets type I (VDDR I) (OMIM 264700) is a rare hereditary condition caused by a mutation in CYP27B1. Vitamin D is emerging as an important risk factor for susceptibility to multiple sclerosis (MS), but there have been no studies on the possible association between hereditary rickets and this disease. Objective: To investigate the association between VDDR I and MS. Design: Case studies. Setting: Haukeland University Hospital, Bergen, Norway. Patients: Three patients in 2 families with a cooccurrence of VDDR I and MS. Results: All 3 patients had VDDR I verified by genetic testing and fulfilled the Poser criteria for MS. Two of the patients have undergone magnetic resonance imaging, which confirmed the diagnosis of long-lasting MS. Conclusions: Vitamin D -dependent rickets type I is a very uncommon genetic subtype of rickets. We have identified 3 patients with this disease who later developed MS. We propose that VDDR I and possibly other hereditary rickets mutations that influence vitamin D metabolism could be risk factors for this disease.