Selective exposure to parental smoking at an early age may increase MS risk in the general population, according to a new study. The findings shed light on a less documented aspect of the risk of developing MS.

MS is an inflammatory, demyelinating disease of the central nervous system, the onset of which typically occurs in people between the ages of 20 to 40. The disease can also develop earlier in life during childhood or later in people older than 50.

Using the data collected within the Environmental Risk Factors in Multiple Sclerosis study, a large multinational case-control population-based study, researchers investigated the link between MS and smoking habit, maternal smoking during pregnancy, and maternal or paternal smoking in Canadian, Italian, and Norwegian populations.

Researchers observed a link between MS and maternal smoking during pregnancy and maternal smoking among Norwegians. A tendency for paternal smoking to be linked with MS was found among Canadians, while no significant link to parental smoking was detected in the Italian population.

Researchers said selective exposure to parental smoking at an early age may differentially increase MS risk in the general population and independently from the subject’s past or current smoking habit. However, the absence of a link between MS and past exposure to parental smoking in some populations may reflect its smaller effect on MS risk compared to other factors.

The study’s authors said there are a lot of genetic and environmental risk factors that interact with each other in MS. The timing of exposure to environmental factors, for example breastfeeding or infections such as mononucleosis, are also important. During the early stages of life, an infection may be protection, but later in life it can be a risk factor. The susceptible period is believed to be in the early stages of life because the immune system is still developing in that phase. So endogenous factors may affect its development.

While active smoking is a known risk factor for MS development and poor prognosis, the effect of past exposure to parental smoking, including maternal smoking during pregnancy, had not yet been properly defined.

The researchers wanted to study if parental smoking could be linked to MS status because knowledge in this field is scarce. If one compares two studies that have recently been published on maternal smoking during pregnancy, they say the opposite. One says there is no association, while the other concludes that children of mothers who smoked had a higher risk of developing MS. Research must distinguish between maternal smoking that happens in the prenatal phase, and parental smoking which is passive smoking during childhood. Another factor to be considered is if your parents smoke, you are more predisposed to becoming a smoker, which affects the risk of developing MS.

The authors believe future research should continue to explore MS risk factors, but also patient prognosis. Association with parental smoking needs to be investigated further, as other fields of medicine suggest that exposure to parental behavior may affect the child’s risk of developing non communicable diseases, such as diabetes and cardiovascular diseases.

The study was presented at EAN 2024, the 10th Congress of the European Academy of Neurology, in Helsinki, Finland.