Familial environment does not influence MS risk

Non-genetic factors influencing MS risk are most likely acting at a broad population level rather than in the familial microenvironment, according to Canadian researchers.The researchers examined the influence of common familial environment on MS risk by studying stepsiblings who had "migrated" into families in which at least one of the children subsequently developed MS. They analysed data from the Canadian Collaborative Project on Genetic Susceptibility to MS (CCPGSMS) that includes information on 19,746 index cases. A total of 687 stepsiblings of index cases were identified, of which four were initially reported to have MS. This represented a several-fold increased MS risk for stepsiblings compared with the general population. Upon further investigation, the authors found that two of the stepsiblings reported by the index case to have MS had no history of any neurological signs or symptoms suggestive of MS or any other neurological condition. Another stepsibling was originally diagnosed with possible MS, but MRI results were negative and the individual remained clinically asymptomatic. The remaining stepsibling was confirmed to have MS, resulting in a risk of MS in stepsiblings of 1/687, which the authors say is, "indistinguishable from that of the general population".There were no cases of MS among the 350 stepsiblings who had either cohabited or had limited contact with the MS index cases up to 15 years of age, and the one stepsibling with MS established contact with the index case after 21 years of age. The authors say these data correspond with the results from an adoption study and studies in half-siblings that have showed no risk attributable to common childhood habitation. A large conjugal study has also showed no increased risk through common exposure in the adult years.The authors note, "The results presented here once again demonstrate the importance of ascertainment and of detailed scrutiny of reportedly affected family members with respect to diagnosis." They conclude that their data adds to existing data, "showing that the action of environment in influencing MS risk is operative at a population level."Reference...