Migration and multiple sclerosis in United Kingdom and Ireland immigrants to Australia: a reassessment. II. Characteristics of early (pre-1947) compared to later migrants.

In our recent reassessment we explored the risk of MS by age at immigration in 258 migrants from United Kingdom and Ireland (UKI) to four states of Australia (New South Wales, Queensland, South Australia, and Western Australia) in the period 1947-1981 (Group II). In the present report we have compared their characteristics with 44 cases who migrated before 1947 (Group I), divided into two subsets: Group Ia (15 cases) was rather similar to Group II in age at immigration (means of 20 and 23 years), age at onset (39 and 33 years), and duration from immigration to onset (19 and 10 years). Group Ib (29 cases) was significantly different from Group II, with mean ages of 4 years at immigration and 40 years at onset, for a mean interval of some 35 years between immigration and onset. All onsets in Group Ib occurred after 1947. We concluded that the Group Ib cases had most probably acquired their MS in Australia. Immigrants from high MS risk countries, including UKI, were modest in number before 1947, but some 770,000 entered from 1947-1981. They may have been the source of MS for the Group Ib migrants.