It sounds simple. But since analysis of the genetic determiners of multiple sclerosis began in the '70s, sunlight's factoring in the disease has seemed irreconcilable with its highly complex genetic make-up.

New research from scientists based at The Westmead Institute in Sydney has drawn a link between the genetic and environmental circumstances of multiple sclerosis, which affects 2.1 million people worldwide, most of whom are diagnosed between 20 and 40 years of age.

The project led by immunologist Dr David Booth capitalises on data from a landmark 2013 study that profiled the DNA of 30,000 MS patients worldwide. The study found there are more than 100 genetic risk factors of MS, which is characterised by the scarring of tissue in the central nervous system.

"Previously, it was thought that t-cells orchestrated an attack on the myelin sheath around nerves, causing their destruction," Dr Booth said. "Because we have found out the gene risk types, we now know there are various immune cells involved in this process, and different sub-sets of cells causing MS in different people."

Dr Booth and his team worked backwards to find the cellular source of two of the 110 genes associated with MS, called EOMES and TBX21.

Using blood samples from 50 patients of Westmead Hospital, they were able to identify the immune cell CD56+ as largely responsible for expressing the two risk factor genes. In MS patients, CD56+ cells were found to be inactive or deficient compared with the general population.

"The study has shown that whether these risk factor genes are turned on or off in the CD56+ cell, it is related to Vitamin D activation," Dr Booth explained.

"It's the first time we have been able to link the genetic risk factors of MS to environmental factors (ie. the absorption of sunlight) and this provides the possibility of new therapeutic pathways."

Booth stated that the team is yet to see whether enhancing Vitamin D activation will begin to turn on the genes expressed by the CD56+ cells, and whether this will alter multiple sclerosis symptoms.

"Potentially this research could lead to finding an environmental trigger for the disease or therapies that slow or prevent relapse of MS that are safer or more effective than those currently available," Booth said.

Hereditary and stable, TBX21 and EOMES genes could also be used as markers of MS patients who will respond to drugs targeting the CD56+ cell.

Dr Booth will be presenting the institute's findings at the International Congress of Immunology in Melbourne on Tuesday.