Rats altered to carry human genes that make a protein associated with some kinds of arthritis develop the symptoms of those human disorders.

A team of scientists said they have produced strains of rats whose cells contain a human protein, HLA-B27. The 8 percent of people who inherit the genes for the protein are at much higher than average risk of developing a family of diseases that includes ankylosing spondylitis, inflammatory arthritis and arthritis associated with the skin disorder psoriasis.

The team, led by Joel D. Taurog and Robert E. Hammer of the University of Texas Southwestern Medical School, inserted the pair of genes needed to produce HLA-B27 into fertilized rats' eggs. Some eggs developed into rats whose cells carried the protein on their surfaces. Their descendants developed inflamed joints, diarrhea and skin rashes similar to psoriasis -- symptoms much like those suffered by some human carriers of the genes.

By studying the rats, researchers may be able to determine whether genetics alone is responsible for such disorders, or whether an environmental trigger like an infection is necessary.

The work, funded in part by the National Institutes of Health and the Howard Hughes Medical Institute, was reported Nov. 30 in the journal Cell.