Scientists have genetically engineered rats with a disease similar to a form of human arthritis, a step that may help find the cause and improve treatments for the disabling illness, it was reported Thursday.

The research has created a new model for scientists researching a form of arthritis. Previously experiments had to be done in mice with symptoms that were not close to those found in humans."For me the rats are the result of a 10-year quest," said Dr. Joel Taurog of the University of Texas Southwestern Medical Center, where the research was conducted.

An estimated 37 million Americans suffer from arthritis. About 500,000 of those patients suffer from spondyloarthropathies, which include crippling spinal ailments, disorders striking children and writer's syndrome, which affects the eyes, urinary tract, fingernails, finger joints and skin.

"It is a startling, significant finding," said Dr. Lawrence Shulman, director of the National Institute of Arthritis, Musculoskeletal and Skin Diseases in Bethesda, Md., at a crowded news conference in Dallas.

In addition to providing an animal model, Shulman said the study "indicates genes are directly responsible in the pathogenesis (cause) of multiorgan diseases like (arthritis)."

Because the disease spread so rapidly in the genetically engineered rats, scientists said they think arthritis is largely caused by heredity, not environmental factors.

In research published in the journal Cell, Taurog and his colleagues said they inserted two human genes implicated in causing spondyloarthropathies into fertilized rat eggs, causing the eggs to produce a protein, dubbed type HLA-B27.

The team found that the rats produced from the genetically engineered eggs developed "arthritis symptoms appeared almost instantly."

"What surprised all of us was the fact the rats developed diseases just as we see in humans, affecting the eyes, heart, genital tract and so forth," Shulman said.

Officials said they planned to use the same process to create rat models for other forms of arthritis.