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Besides demonstrating the power and the feasibility of using half-sib studies to throw light on the aetiology of complex disorders,our findings show that a shared environment does not account for familial risk in MS and that maternal effects(such as intrauterine and perinatal factors, breastfeeding,and genomic imprinting)have no demonstrable effect on familial risk.Having the number of potentially contributory genes(by comparing full-sib and half-sib rates)lowers the risk of MS by a factor of 2*62,an observation consistent with a polygenic hypothesis. |
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