Study Provides Proof for New Rheumatoid Arthritis Gene

Mutant PTPN22 allele is over-transmitted in rheumatoid arthritis patients

TUESDAY, Jan. 23 (HealthDay News) -- The PTPN22 gene, which is associated with type 1 diabetes, is also a cause of rheumatoid arthritis, according to the results of a new study reported in the Jan. 19 Proceedings of the National Academy of Sciences Early Edition. The finding suggests the gene may play a role in a number of autoimmune diseases.

PTPN22 has been previously associated with rheumatoid factor-positive (RF+) rheumatoid arthritis and other autoimmune diseases, but the link has not been solidified by genetic studies. Using a sample of 1,395 Western European individuals from 465 families (one rheumatoid arthritis case and both parents), Laetitia Michou, M.D., of University Evry-Paris 7 Medical School in France, and colleagues sought linkage proof for the association.

The PTPN22-1858T allele was over-transmitted in RF+ families (63 percent), a departure from Mendel's law (50 percent transmission from heterozygous parents) and the proof needed to identify PTPN22 as a new susceptibility gene, according to the report. Further, the allele frequency increased from 11 percent in control subjects to 17.4 percent in RF+ rheumatoid arthritis subjects and was paralleled by an increase in susceptibility genotype.

"Together with the literature, this study provides the final piece of the 'association and linkage proof' for PTPN22 as the second RA gene" and "for PTPN22-1858T as an autoimmunity susceptibility allele," the authors write.

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