Prevalence (probability) of genetic susceptibility in populations in different geographic regions.

‡Per 100,000 population. The prevalence of MS (i.e., the measure used to estimate PMS) for each region is taken from data provided in [51]. A range is given because, often, a range of estimates are available for a particular region.
*Studies (9,11, and 12) reported pair-wise monozygotic-twin (MZ) concordance-rates and these have been converted into proband-wise rates assuming a random sampling of twin-pairs (see Appendix S1). Also, the error associated with the estimate of CRMZ for each region has not been taken into account.
**Calculated according to Equation (3):

See text for details. Because the prevalence of possessing at least one copy of the HLA DRB1*1501 susceptibility allele is 30% in the general populations of northern Europe and northern North America(i.e., PHLA+) and 55% in the MS populations(i.e., PHLA+ MS) from these regions [2], [103] and assuming approximately equal penetrance for the different susceptibility genotypes [10], the observation that (PG≈0.5%) indicates that only about 1% of individuals who carry this allele are even susceptible to MS. Thus:
.
***Because both men and women come from the same Canadian population, the actual disease prevalence is irrelevant and, therefore, a range of estimates is unnecessary. Nevertheless, the current prevalence of MS in Canada (for the purpose of these calculations) was taken to be 100 per 100,000 population [10] and divided according to the current sex ratio of 3.2∶1 in Canada [65].