Why are women more likely to get arthritis?

A 'master switch' that makes women more prone to arthritis has been identified by scientists.

Experts say the discovery of the key gene that controls the immune network paves the way for a drug that targets it.

Women represent nearly eight out of every 10 cases of autoimmune diseases - caused by cells attacking the body's own tissue.

Despite the huge gulf between the sexes being well known, researchers had struggled to determine why it existed.  

Now they have pinpointed the master regulator of a woman's immune system - and have called it VGLL3.

The study, published in the journal Nature Immunology, went in a different direction to the usual research on sex hormones.

The researchers, from the University of Michigan, investigated the gene expression in the skin of healthy subjects, including samples from 31 females and 51 males.

They found that 661 genes in total were expressed differently between the sexes.

Many of those had immune function and overlapped with genetic pathways and risk genes, co-author Dr Yun Liang said.

This allowed the team to discover VGLL3. 

Lead researcher Professor Johann Gudjonsson, said: 'This previously unknown inflammatory pathway promotes autoimmunity in women.

'We found a completely new angle. Our team identified a gene expression difference between the sexes that is associated with susceptibility to autoimmune disease.'

Autoimmune diseases take many forms across the body from psoriasis patches on the skin to lupus throughout the body to rheumatoid arthritis in the joints.

But all affect women at a higher rate and it often takes years to get a correct diagnosis.

Much of the existing work on gender differences in autoimmune diseases has focused on sex hormones. 

However, the novel inflammatory pathway the researchers identified as VGLL3 is not hormonally regulated. 

Professor Gudjonsson said: 'We found no evidence of involvement of oestrogen or testosterone in the immune differences we observed between women and men.

'Identifying a separate regulatory mechanism could be a huge advance in gender-focused autoimmune research.' 

He added: 'Learning more about these disease processes in each gender will provide opportunities for therapeutic interventions we did not imagine before, including both prevention and treatment.'  

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