J Neurol (2011) 258:1140–1149 DOI 10.1007/s00415-010-5898-4 O R I G I N A L C O M M U N I C A T I O N Migration and multiple sclerosis in immigrants to Australia from United Kingdom and Ireland: a reassessment. I. Risk of MS by age at immigration J. G. McLeod • S. R. Hammond • J. F. Kurtzke Received: 21 September 2010 / Revised: 21 December 2010 / Accepted: 27 December 2010 / Published online: 25 January 2011 The Author(s) 2011. This article is published with open access at Springerlink.com Abstract A previous study of the prevalence of multiple sclerosis (MS) in 1981 among immigrants from the United Kingdom and Ireland to Australia found that the prevalence for those with age at immigration (AAI) under 15 years of age did not differ from the older immigrants. We have reanalysed the original materials as well as census data for 1901–1981 for UKI and other high MS risk country immigrants. There was a highly signiﬁcant trend in the prevalence rates of all Australians from New South Wales (NSW) to South Australia (SA) to Western Australia (WA) to Queensland (QLD). Rates by state among the Austra- lian-born were almost identical to these, but there was no prevalence gradient for the UKI-born. The denominator population at risk of MS by AAI was calculated from special census tables of length of residence in Australia by age 0–79 in 1981 for UKI immigrants 1947–1981. The numerator was limited to the subset of 258 MS (Group II) also immigrating in 1947 and later, and age 0–79 in 1981. The absolute risk of MS for these migrants to the four J. G. McLeod (&) Department of Medicine, University of Sydney, Camperdown NSW 2006, Australia e-mail: james.mcleod@sydney.edu.au J. G. McLeod Institute of Clinical Neurosciences, Royal Prince Alfred Hospital, Camperdown NSW 2050, Australia S. R. Hammond Maynooth Neurology, Orange NSW 2800, Australia e-mail: hammond@ix.net.au J. F. Kurtzke Emeritus, Neurology, Georgetown University, Washington, DC, USA e-mail: kurtzke2@aol.com 123 states entering at age 0–14 was 22/100,000, signiﬁcantly less than for all older age groups; age 15–39 immigrants had a risk of 54/100,000. Similar risk ratios for 0–14 versus 15–39 by state were 31 versus 61 (NSW), 29 versus 44 (QLD), 11 versus 50 (SA), 15 versus 51 (WA). Keywords Immigration Multiple sclerosis Prevalence Risk Australia Introduction In our earlier work1, the prevalence in 1981 of multiple sclerosis (MS) in migrants from the United Kingdom and Ireland (UKI) to Australia was compared to that in the Australian-born population, and it was found that there was a similar and signiﬁcant correlation of prevalence with latitude in both groups [1]. However, in contrast to some other studies of migrants from high MS areas to low [2–6] there was no signiﬁcant difference in the prevalence of MS between those migrating under age 15 and those then older. In the present study we have re-examined the 1981 data in order to address more speciﬁcally in these UKI immi- grants to Australia the original proposition [7, 8] that in high frequency MS areas, like UKI, the risk of developing MS has already been determined largely by the age of about 15 years, and emigrants under that age to lower frequency areas, like Australia, would therefore have acquired their disease in their new place of residence and at the lower rate characteristic of this new location. 1 All current authors had agreed with the conclusions of the 2,000 paper; JFK had been provided the original numerator data and tables at that time.