WASHINGTON — Nearly half of the effects that contribute to knee osteoarthritis can be explained through heritable traits, Guangju Zhai, Ph.D., reported at the annual meeting of the American College of Rheumatology.
In a group of 114 monozygotic and 195 dizygotic twin pairs (all white females) from the Twins UK registry, heritability accounted for 49% of the total variance of joint space narrowing in the knee and for 47% of osteophytes. The results did not change substantially after adjustments were made for age and body mass index, said Dr. Zhai of St. Thomas' Hospital, London. At baseline and at a follow-up of about 7 years, radiographs of the anteroposterior aspect of patients' knees were obtained while in extension and bearing weight. A full lower-limb x-ray was obtained at the follow-up visit.
About 20% of the patients had joint space narrowing and osteophytes at baseline. About 30% had progression of joint space narrowing or osteophytes at follow-up.
Genetic effects explained 65% of the total variance in knee alignment. Statistical analyses showed that the heritability estimate for knee alignment remained the same after adjustments were made for the presence of knee osteoarthritis, which suggests that they are not likely to share common genetic control.
The heritability of the progression of joint space narrowing or osteophytes appeared to be stronger than heritability was for the mere presence of either sign. About 80% of joint space narrowing could be accounted for through heritable traits, while osteophyte progression was 62% heritable. Adjustments for age and BMI did not change the heritability of joint space narrowing progression, but decreased the heritability of osteophyte progression to 50%, Dr. Zhai said.