Early-life hygiene-related factors affect risk of central nervous system demyelination and asthma differentially

The increasing prevalence of immune-related diseases, including multiple sclerosis, may be partly explained by reduced microbial burden during childhood. Within a multi-centre casecontrol study population, we examined: (i) the co-morbid immune diseases profile of adults with a first clinical diagnosis of central nervous system demyelination (FCD) and (ii) sibship structure in relation to an autoimmune (FCD) and an allergic (asthma) disease. FCD cases (n=282) were aged 1859 years; controls (n=558) were matched on age, sex and region. Measures include: history of doctor-diagnosed asthma; sibling profile (number; dates of birth); and regular childcare attendance. FCD cases did not differ from controls with regard to personal or family history of allergy, but had a greater likelihood of chronic fatigue syndrome [odds ratio (OR)=3 center dot 11; 95% confidence interval (CI) 1 center dot 11, 8 center dot 71]. Having any younger siblings showed reduced odds of FCD (OR=0 center dot 68; 95% CI: 0 center dot 49, 0 center dot 95) but not asthma (OR=1 center dot 47; 95% CI: 0 center dot 91, 2 center dot 38). In contrast, an increasing number of older siblings was associated with reduced risk of asthma (P trend=0 center dot 04) but not FCD (P trend=0 center dot 66). Allergies were not over-represented among people presenting with FCD. Sibship characteristics influence both FCD and asthma risk but the underlying mechanisms differ, possibly due to the timing of the putative sibling effect'.