ABSTRACT
Women who have MS themselves or whose partners have MS should be counselled that the risk of MS developing in their offspring is 3% to 5%, compared to a 0.2% for an individual who does not have a parent with MS, a 15 to 25 times increased risk. Should both parents have MS, this increases to 29.5%, a 147.5 times increased risk compared to the general population. An adopted child of an affected individual has no greater risk than the general population (18) suggesting that this increased risk in families is due to genetic rather than environmental factors. However, the risk of inheriting MS does appear to be influenced by environmental factors during pregnancy. For example, in the northern hemisphere the risk is increased in children born in spring and reduced in winter (19,20), with this being mirrored in the southern hemisphere (21). The mechanism for this difference remains unclear but the comparatively reduced exposure to sunlight, and thereby vitamin D, during pregnancy has been proposed. The hypothesis that vitamin D deficiency may be a risk factor for MS has also been supported by the finding that vitamin D has immunomodulatory effects and may regulate the MHC (22).
