One study reported incidence rates for MS among immigrants to Israel. Those who came from Africa and Asia, where the rates are low, continued to have a low risk of developing MS in Israel. However, the situation was quite different for immigrants from Europe, where incidence rates were moderate to high. If they migrated as children, their risk of developing MS in Israel was low – similar to that for the Israeli population. However, if they migrated after 15 years of age, their subsequent risk of developing the disease was high – similar to that for their home country. These data suggest that there is some exposure that occurs during childhood, and is more prevalent in European countries, that increase the risk of developing MS after puberty.