GLOBAL: Sunlight the answer to MS

More than 250 researchers in 15 countries, along with 10,000 patients, have taken part in one of the longest and largest human genetic studies ever undertaken into the cause of the devastating neurological disease, multiple sclerosis or MS.

Among the most common nerve diseases to attack 20- to 40-year-old adults, MS affects 2.5 million people worldwide, most of them women. A possible cause could be lack of vitamin D, which humans generate in the sun.

The latest results of the research were published last month in the journal Nature. Australian researchers have played a significant role in the work, having contributed more than 1,000 DNA samples to the international study.

A report on the research says the scientists identified 29 new genetic variants and confirmed the presence of 23 previously known genetic associations in the human genome.

A remarkable pattern has been revealed, showing that the reason why some people get MS and others do not is largely because of subtle, inherited differences in a person's immune system. The report identifies a pivotal role for T cells - the 'orchestra leaders' of the immune system in driving MS.

"The consensus is that those cells - the inflammatory cells - are actually what's driving the disease, causing the nervous system damage," says Professor Trevor Kilpatrick who heads the Centre for Neuroscience at Melbourne University

Although the cause of MS has yet to be discovered, it is known that in a person with the disease the body's immune system attacks its own myelin, the protective insulation surrounding the nerve fibres in the brain and spinal cord. This causes disruption to nerve transmission, just as the loss of insulation around an electrical wire interferes with the transmission of signals.

For those suffering MS, simple activities such as seeing, walking, feeling, even thinking, or controlling the bowel and bladder, are affected when nerves are prevented from 'firing' properly and are potentially eventually destroyed, leaving the person severely disabled.

Scientists discovered the first MS gene, believed to be one of the main contributing factors to the disease, in 1972 but it was another 35 years before a second gene was identified. Then, in 2009, an Australian-New Zealand group of researchers called the ANZgene consortium and including members of Kilpatrick's multiple sclerosis group, were involved in research in a genome-wide scan that analysed DNA from 5,000 MS patients in the two countries.

This study led to the identification of two novel 'susceptibility loci' for MS and the group is now undertaking further work to try to discover how the relevant genes alter a person's predisposition to multiple sclerosis. Interestingly, the ANZgene study located a susceptibility locus on chromosome 12 that encompasses a gene that modifies vitamin D metabolism while the recent international study identified a second such gene.

These discoveries point to a connection between genetic and environmental risk factors because previous research has suggested a link between vitamin D deficiency and an increased risk of multiple sclerosis.

Kilpatrick says three times as many young women as men contract MS and that the further south in Australia and New Zealand they live, the greater their chance of becoming affected.

Related research conducted by medical scientists in Tasmania and New Zealand looked at the geography of the spread of MS - how it varies by latitude and the extent to which the disease is increasing.

The research found a definite increase in the incidence of MS in Tasmania over the last 25 years and that this has been largely driven by a rise in the number of women with MS. Studies in New Zealand have also revealed a significant risk of women developing MS the further south they live, with the risk enhanced if the female is of north-west European origin.

Vitamin D is produced in humans by ultraviolet radiation in sunlight falling on the skin But the further south a person in the southern hemisphere goes, winter sunlight levels fall to such an extent the body cannot produce any vitamin D.

Another group of scientists in the Ausimmune consortium, of which Kilpatrick is also a founding member, has recently completed a multi-centre epidemiological investigation aimed at identifying the environmental factors likely to cause MS.

Researchers in four regions of Australia attempted to recruit every person experiencing the early stages of MS, to match those with control groups of people free of MS and to understand the life events for those individuals and how they might differ.

"We have identified a reduction in key exposures to ultraviolet radiation in earlier life for people who develop MS. And consistent with this, the vitamin D levels are lower among those with a clinical presentation of the disease," Kilpatrick says.

"So the hypothesis at the moment is that UV radiation and, as a consequence, vitamin D might be relevant to susceptibility to MS although there may be a second element to UVR independent of vitamin D which drives susceptibility, as well. With vitamin D deficiency definitively identified as a risk factor, we're working out how to determine the best way to investigate whether vitamin D supplements reduce the risk of developing MS."


COMMENT

This is a an interesting and informative article, but the headline that sunlight is 'the answer' to MS gives it a tabloid quality that cheapens the story.

D Cornell