Type 1 Diabetes Associated With Anti-CCP-Positive Rheumatoid Arthritis
In addition, both diseases were associated with the 620W allele of the protein tyrosine phosphatase N22 (PTPN22) gene, prompting the researchers to suggest that this gene variant might "represent a common pathway for the pathogenesis of these two diseases."
"This provides the first evidence for an association between these diseases at a population level," coauthor Dr. Katherine P. Liao of Brigham and Women's Hospital, Boston, told Reuters Health. "The fact that a genetic factor like PTPN22 contributes to the risk of both RA and type 1 diabetes suggests that these diseases may share a common disease pathway. Identification of important, shared disease mediators is an important goal for both disease prevention and the development of therapeutics."
This report comes from the Epidemiological Investigation of RA, a long-term population-based Swedish study that recruited RA patients, aged 18-70 years, who were diagnosed between May 1996 and December 2003. Each patient was matched according to age, sex and location of residence to a control subject randomly selected from Sweden's national population registry.
In all, 1,419 patients and 1,674 controls answered a questionnaire that addressed diabetes, its treatment and other topics. Of this total study population of 3,093 participants, 71% were female.
Sixty-two RA patients (4.4%) reported having diabetes, 22 with type 1 and 42 with type 2, versus 51 of the controls (3.1%), 5 with type 1 and 46 with type 2. Self-reported type 1 diabetes was associated with an increased risk of RA, but the increase was seen only in patients with anti-CCP-positive RA.
Statistical adjustment for the presence of the 620W PTPN22 allele attenuated somewhat the risk that an individual with type 1 diabetes would develop anti-CCP-positive RA, from an odds ratio of 7.3 to 5.3. Previous studies had shown the PTPN22 allele to be a risk factor for both type 1 diabetes and for anti-CCP-positive RA.
Arthritis Rheum 2009;60:653-660.