Mikaeloff Y et al. (2007) Parental smoking at home and the risk of childhood-onset multiple sclerosis in children. Brain 130: 2589–2595

Smoking is associated with the risk of developing multiple sclerosis (MS) in adults, but the effects of passive smoking in children are unclear. To address this issue, Mikaeloff et al. studied children with MS and matched controls to investigate whether exposure to parental smoking in the home increased the risk of a first episode of MS before 16 years of age.

This study enrolled patients with confirmed MS who had experienced a first clinical episode before the age of 16 years and at least one relapse. Each case was matched on the basis of age, sex, and current area of residence with 12 controls from the French general population. Participants were each sent a questionnaire about environmental risk factors, incidence of familial autoimmune diseases, socioeconomic status, and whether one or both parents had ever smoked within the home before the index date (i.e. onset of the first episode of MS in case patients).

The frequency of exposure to parental smoking in the home was 62.0% for the 129 case patients and 45.1% for the 1,038 controls. Exposed children had a higher risk of a first episode of MS than did those who were not exposed (rate ratio [RR] 2.09); this effect persisted after adjustment for socioeconomic status and for familial MS or other familial autoimmune diseases (RR 2.12, 95% CI 1.43–3.15). The adjusted risk was higher in older children (≥10 years of age), who had a relatively long duration of exposure to cigarette smoke, than in younger individuals (RRs 2.49 and 1.47, respectively).

The authors conclude that exposure to parental smoking increases the risk of a first episode of MS before the age of 16 years, and that this risk increases with increasing duration of exposure.