4 July 2005

Rheumatoid arthritis gene link proven

The gene PTPN22 has been confirmed as one of the factors that cause rheumatoid arthritis by University of Otago researchers.

“This is only the second gene in the past 25 years to be universally accepted as a gene associated with the susceptibility for arthritis,” Department of Biochemistry Senior Research Fellow Dr Tony Merriman says.

The finding has just been published in the leading international arthritis research journal Arthritis and Rheumatism.

The research was funded by the Health Research Council of New Zealand and Arthritis New Zealand.

The gene was first identified last year as potentially being instrumental in causing rheumatoid arthritis, and Dr Merriman’s study is one of the first studies to replicate - and thus validate - the original findings.

“The initial finding is only half the story. It’s only when that finding has been replicated convincingly that the initial paper becomes of more importance, and I am delighted that we have been able to do that,” Dr Merriman says.

“This is the culmination of six years of collecting samples and I want to thank the many hundreds of people with and without rheumatoid arthritis from around New Zealand who generously gave DNA samples. The New Zealand Rheumatology Research Network also played a critical role.”

The resultant DNA database will play an important role in replicating other international findings and generating new findings, as a large sample group is vital to ensure results are reliable.

Confirmation that the gene plays a definite role in rheumatoid arthritis means research pharmacists can study the gene’s mechanism and where its messages break down in order to develop drugs to correct the defect.

“Previously we knew rheumatoid arthritis was an immune disease but the immune system is so huge and complex it is difficult for researchers to know where to look – or necessarily what was a cause and what was a result of the disease. Now we have a real starting point for research into treatment as we know that PTPN22 is a cause.”

PTPN22 plays an important role in limiting the activity of the immune system’s soldier cells, T lymphocytes, which attack and destroy foreign cells. In rheumatoid arthritis T lymphocytes get out of control and initiate and drive the attack on the body’s own cells.

“So it would seem that the message to control the T lymphocytes and stop attacking the joints becomes faulty,” Dr Merriman says.

- Rheumatoid arthritis is a debilitating autoimmune disease where the body attacks itself in the joints, causing inflammation, stiffness and pain. It affects one in 50 New Zealand adults.

- PTPN22, is also over-represented in people with Type 1 diabetes and thyroiditis, providing extra evidence it is a causal factor in autoimmune diseases generally.

ENDS