The numbers of people being diagnosed with multiple sclerosis is rising worldwide, though distinct differences in factors thought to drive this rise are evident among regions, according to MS data represented by researchers on patients in Asia, Latin America, and the Australia-New Zealand.
The data was part of the session “Prevalence and phenotype evolution of MS in different continents,” that opened the 7th Joint ECTRIMS-ACTRIMS Meeting, taking place in Paris through Saturday.
Across Asia, the greatest increase in newly diagnosed MS patients is in Japan, researchers reported. That country today has 20,000 people with MS or neuromyelitis optica (an autoimmune disease affecting the optic nerves and spinal cord), compared to 1,000 in 1980.
New MS cases far outnumber those of neuromyelitis optica, said Yamamura Takashi with the Department of Immunology, National Institute of Neuroscience, Japan, who presented the data.
Bt this “increase is not because of better [disease] awareness,” Takashi said, citing findings in a recent study, nor could it be explained by improved healthcare management.
Researchers in Japan have also failed to find connections between MS risk factors — like smoking, lower exposure to sunlight, Epstein-Barr virus infection, or higher salt intake — and the increased rates of the disease.
Instead, Takashi suggested that a “Westernization” phenomenon, particularly in terms of diet and lifestyle, might be related to the higher rates of MS in the Japanese population.
In fact, “12.5% of Japanese MS patients” were living in the West “at MS onset,” he said.
A change in diet might negatively impact gut bacteria (flora/microbiota), and hence, immune processes, Takashi said. “Your flora is your friend,” he emphasized.
Several research studies, indeed, have shown a link between gut bacteria and MS, and “alterations in the gut microbiota (dysbiosis) were confirmed in Japanese patients with MS,” Takashi said. Specific bacteria thought to be beneficial, like Prevotella, were found to be significantly reduced in MS patients.
“It is possible that changes of eating habits in Japan are responsible for dysbiosis and dysregulation in the immune network, leading to the increase of MS patients,” Takashi said, concluding his presentation.
Among the countries of Latin America, studies of how common MS is vary greatly, likely mirroring the differences in altitude, climate, sun exposure, ethnicity, and economic development to be found there, said Laura Negrotto, with the Institute for Neurological Research Dr. Raul Carrea (FLENI), Argentina, who presented data at the session.
MS is increasing in Latin America much as it is worldwide, and people farther from the equator are at greater risk of developing the disease — again, much as is seen among people living in northern latitudes. But Negrotto underscored that researchers have also seen a number of exceptions — suggesting that genetic or environmental factors do influence disease risk.
A difference is also increasingly evident between the sexes, with more women developing the disease than men.
Genetic factors are particularly interesting to study in Latin America, because its populations are composed of descendants of Native Americans, Africans, and Europeans/Caucasians. Across Latin America, Negrotto said, you find a “complex population,” the result of “five centuries of admixture.”
Studies suggest that MS is more common in those countries where people of European descent make up the majority, and less common in areas dominated by Native Americans.
But countries and regions there also differ in socioeconomic status, which may impact exposure to infections, which, in turn, can influence MS rates.
Cases where MS runs in families are less common in Latin America that elsewhere, Negrotto said, adding that many challenges exist to MS population studies there. These include the region’s poorer economic development, which in many countries limits access to specialized MS clinics, and the fact that MS is a less common disease across Latin America than elsewhere, with only a few countries reporting incidence rates, she said.
Concerning the link between UV exposure, vitamin D levels and MS risk, Negrotto noted that “UV radiation is higher in Latin America” that elsewhere, but it’s “still not clear if vitamin D is linked to MS” across the region.
While Latin America is a mix of people with different ancestries, Australia and New Zealand is dominated by people of Northern European descent (Caucasians, mostly an Anglo-Saxon population). The prevalence of MS in Australia is also rising, and in contrast to the effects that varying latitudinal may have on cases reported in Latin America, the region demonstrates a robust gradient in MS rates from north to south.
“There is a prospectively proven strong latitudinal incidence gradient in Australia,” said Helmut Butzkueven, with the Department of Medicine at the University of Melbourne, in the presentation.
“Environmental factors drive the gradient in the region, particularly since population is genetically homogenous,” Butzkueven added.
People in tropical North Queensland, close to the equator, are 6.5 times less likely to develop MS compared to those in southern Tasmania, he noted.
In nearby New Zealand, research also shows that latitude appears to impact the risk of relapsing-remitting MS in women, specifically, but does not greatly alter risk for primary progressive MS.
Different from other regions in the world, “Australia and New Zealand are NOT experiencing a change in sex ratio,” or differences in disease rates between men and women, Butzkueven said. The ratio there is about 2.5:1, women to men.
The researcher also emphasized that Australian studies have shown a link between low vitamin D levels and new MS cases, suggesting a “relationship between UV radiation, vitamin D levels and MS incidence.” Further studies are underway into this possible association.