April 18, 2013 | News | Living with MS MS Research

Is MS different in blacks?

Part 1

Multiple sclerosis (MS) primarily affects women of European descent and it’s often assumed that it’s fairly rare in other people. But MS can develop in people of non-European ancestry – and its effects can be particularly devastating. One often overlooked group is people of African ancestry.

In Africa itself, MS is considered to be extremely rare in the black population. There were isolated cases reported in Kenya, Uganda, and Ethiopia as far back as 1946, but they were noteworthy because they were so unusual (Goldstein. East Afr Med J 1946;23:170-173). In South Africa, MS among blacks was said to be “unknown” as recently as 1979 (Ames & Bowen J Neurol Neurosurg Psychiatry 1979;42:731-733). The first documented case there was reported in 1987 (Bhigjee. S Afr Med J 1987;72:873-875). In 1994, when researchers decided to compile all known cases of MS among blacks in South Africa and Zimbabwe, they could find only 12 people (Dean and colleagues. J Neurol Neurosurg Psychiatry 1994;57:1064-1069).

MS appears to be a little more common among Afro-Caribbeans. A survey in Martinique identified 62 people with MS, which translated to about 14 people per 100,000 population (Cabre and colleagues. Neurology 2001;56:507-514). This is considered to be a medium-prevalence number. (In comparison, the prevalence of MS in Canada is over 200 per 100,000 – or about 15 times higher.)

A subsequent study by the same researchers reported a very curious finding. When they compared Afro-Caribbeans who remained on the island with those who emigrated to France as children or adolescents, they found that their MS symptoms changed (Merle and colleagues. Eur J Ophthalmol 2005;15:392-399). Eye problems (optic neuritis) were severe in Martinique, but were less so in people who had moved to France. Similarly, for children of West Indians born in the United Kingdom, the MS risk is closer to what you see for people born in Britain rather than those born in the Caribbean (Elian and colleagues. J Neurol Neurosurg Psychiatry 1990;53:906-911).

How common is MS in African-Americans?

One of the first people to look at MS in African-Americans was John Kurtzke, who would later develop the Expanded Disability Status Scale (EDSS) to assess disability in MS. Kurtzke worked at the Bronx Veterans Administration (VA) hospital in New York, and he realized that military records provided a unique way of investigating MS. So over the next few decades he examined the files of veterans of World War II, Korea and Vietnam who had developed MS (Kurtzke and colleagues. Neurology 1979;29(9 Pt 1):1228-1235; Wallin and colleagues. Ann Neurol 2004;55:65-71).

What he found was that MS was most common in women – and black women were as likely to be affected as white women. This indicated that sex was a more important factor than ancestry when looking at the risk of developing MS.

MS was uncommon in black World War II veterans, but by Vietnam that risk had increased about 50%. It’s well known that MS risk is influenced by a person’s genetics, but a population’s genetics don’t change quickly enough for the MS risk to increase 50% in a generation. So some other factor must be at work. Kurtzke thought that the change was an environmental factor and he would later speculate that MS was actually an infectious disease (Kurtzke. Clin Microbiol Rev 1993;6:382-427).

As in other parts of the world, MS risk showed a strong north-south gradient. MS was less common in the southern U.S. states and highest in the northern states. The dividing line was the 37th parallel; in the east, the dividing line was a little higher north – the 39th parallel (curiously enough the Mason-Dixon line). Among white Americans, part of this effect was attributed to the higher rate of MS seen in people of Scandinavian ancestry who had moved to the Great Lakes states. But this north-south gradient was also seen for African-Americans (Kurtzke & Page. Neurology 1997;48:204-213).

In fact, African-Americans born in the north developed MS about five years earlier than those born in the south and who later moved north (Morariu & Linden. Acta Neurol Scand 1980;62:180-187). This is often attributed to greater sun exposure in the south, but socioeconomics are important as well. Economic status generally predicts health – the richer you are, the longer you’ll live – but MS is different in this respect. MS is more commonly diagnosed in people with higher socioeconomic status, presumably because they have better access to health care, are more likely to report their symptoms to a doctor, and be recorded in an MS patient database (Marrie. Neurol Clin 2011;29:323-341).

So we ignore social and economic factors at our peril. When people talk about how MS symptoms are more severe and disabling in blacks, many of these differences disappear when socioeconomic factors are taken into account (Marrie and colleagues. Neurology 2006;66:1235-1240). One way of removing this factor from the equation is to look at military databases because military personnel have equal access to healthcare.

In a 2011 report by the U.S. Armed Forces Health Surveillance Center, MS wasn’t uncommon in blacks – it was 50% higher in blacks compared to whites (Medical Surveillance Monthly Report, vol. 18, January 2011; free full text at www.afhsc.mil/viewMSMR?file=2011/v18_n01.pdf#Page=12). Part of this may be because there are more men in the military and MS is more common in black males compared to white males, which skews the results somewhat. But this finding raises the disturbing possibility that MS isn’t rare at all in black Americans, but is not being diagnosed and is not being adequately treated.

In Part 2 we’ll look at MS symptoms and how effective the current medications are in African-Americans.

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