Scientists reported on Wednesday they had doubled the haul of genes linked with multiple sclerosis (MS), a crippling but baffling disease of the nervous system. MS, which affects around one person in every thousand, is presumed to have a mix of environmental as well as inherited causes.The immune system attacks myelin, the protective fatty sheath that swathes the nerve fibres. As a result, nerve signals get lost, delayed or disrupted, causing problems in coordination, balance, speech and vision, and the problems worsen as the disease progresses. Publishing in the British journal Nature, an international consortium of researchers identified 29 genes whose variants were strongly associated with MS, plus five other genes also suspected to play a role. The tally adds to 23 genetic variants known to have a part in this complex disease. Many of the newly-identified genes are important in the immune system, either controlling interleukins -- messenger chemicals that facilitate interactions between immune defences -- or T-cells, which attack intruders.In some cases, they have also been fingered in earlier research in other auto-immune diseases, such as diabetes and Crohn\'s. Investigators have previously found that people who are deficient in vitamin D run a higher risk of MS. Bolstering this link, two of the freshly-identified genes play a part in metabolising the vitamin.The probe entailed trawling through the DNA of 9,772 people with MS in 15 countries, and spotting telltale changes in the code when their genomes were compared with 17,376 otherwise healthy counterparts. By netting culprit variants of genes, scientists hope to further fundamental knowledge about MS. The hope is to develop better tools to diagnose the disease and -- eventually -- drugs to protect or even repair the precious myelin.