Multiple Sclerosis in Pregnancy :

Incidence of multiple sclerosis is thought to be increasing, but this notion has been difficult to substantiate. In a longitudinal population-based dataset of patients with multiple sclerosis obtained over more than three decades, we did not show a difference in time to diagnosis by sex. We reasoned that if a sex-specific change in incidence was occurring, the female to male sex ratio would serve as a surrogate of incidence change. Since environmental risk factors seem to act early in life, we calculated sex ratios by birth year in 27 074 Canadian patients with multiple sclerosis identified as part of a longitudinal population-based dataset. The female to male sex ratio by year of birth has been increasing for at least 50 years and now exceeds 3.2:1 in Canada. Year of birth was a significant predictor for sex ratio (p<0.0001, chi(2)=124.4; rank correlation r=0.84). The substantial increase in the female to male sex ratio in Canada seems to result from a disproportional increase in incidence of multiple sclerosis in women. This rapid change must have environmental origins even if it is associated with a gene-environment interaction, and implies that a large proportion of multiple sclerosis cases may be preventable in situ. Although the reasons why incidence of the disease is increasing are unknown, there are major implications for health-care provision because lifetime costs of multiple sclerosis exceed pound1 million per case in the UK.

The influence of pregnancy in multiple sclerosis has been a matter of controversy for a long time. The Pregnancy in Multiple Sclerosis (PRIMS) study was the first large prospective study which aimed to assess the possible influence of pregnancy and delivery on the clinical course of multiple sclerosis. We report here the 2-year post-partum follow-up and an analysis of clinical factors which might predict the likelihood of a relapse in the 3 months after delivery. The relapse rate in each trimester up to the end of the second year post-partum was compared with that in the pre-pregnancy year. Clinical predictors of the presence or absence of a post-partum relapse were analysed by logistic regression analysis. Using the best multivariate model, women were classified as having or not having a post-partum relapse predicted, and this was compared with the observed outcome. The results showed that, compared with the pre-pregnancy year, there was a reduction in the relapse rate during pregnancy, most marked in the third trimester, and a marked increase in the first 3 months after delivery. Thereafter, from the second trimester onwards and for the following 21 months, the annualized relapse rate fell slightly but did not differ significantly from the relapse rate recorded in the pre-pregnancy year. Despite the increased risk for the 3 months post-partum, 72% of the women did not experience any relapse during this period. Confirmed disability continued to progress steadily during the study period. Three indices, an increased relapse rate in the pre-pregnancy year, an increased relapse rate during pregnancy and a higher DSS (Kurtzke's Disability Status Scale) score at pregnancy onset, significantly correlated with the occurrence of a post-partum relapse. Neither epidural analgesia nor breast-feeding was predictive. When comparing the predicted and observed status, however, only 72% of the women were correctly classified by the multivariate model. In conclusion, the results for the second year post-partum confirm that the relapse rate remains similar to that of the pre-pregnancy year, after an increase in the first trimester following delivery. Women with greater disease activity in the year before pregnancy and during pregnancy have a higher risk of relapse in the post- partum 3 months. This is, however, not sufficient to identify in advance women with multiple sclerosis who are more likely to relapse, especially for planning therapeutic trials aiming to prevent post-partum relapses.

Multiple sclerosis (MS) is probably aetiologically heterogeneous. Systematic genetic epidemiological and molecular genetic studies have provided important insights. Both genetic and non-genetic (environment, stochastic) factors may be involved in susceptibility as well as outcome, but we have yet to understand their relative roles. Any environmental factor is likely to be ubiquitous and act on a population-basis rather than within the family microenvironment. Taken together, the results of genome screening studies provide strong evidence for exclusion of a major locus in MS. There are, however, many genes that seem to be associated with MS. These include, but are in no way limited to, HLA classes I and II, T-cell receptor beta, CTLA4, ICAM1, and SH2D2A. The future of MS genetics, as for most common complex disorders, will be dependent on the resources available, ranging from biological samples and comprehensive databases of clinical and epidemiological information to the development of new technologies and statistical methods.