An investigation of the relationship between latitude and multiple sclerosis severity in New Zealand.

Associations between latitude and the prevalence of multiple sclerosis are well recognized,1–3 although the association is not seen in some geographical regions.4 The 2006 New Zealand National Multiple Sclerosis Prevalence Study (NZMSPS)5 reported a three-fold increase in multiple sclerosis prevalence with increasing latitude from northern (37.9°S) to southern (45.8°S) regions of New Zealand. In addition, the study found that of the 2422 subjects assessed, 60% had moderate to severe disability (Expanded Disability Status Score (EDSS)6 score 3.5 to 9.5). There has been little previous investigation of whether disease severity is related to latitude. We therefore investigated, using data acquired in the NZMSPS, whether latitude is associated with disease severity in New Zealand.