Authors respond to criticism of rheumatoid arthritis twin study

doi:10.1136/bmj.325.7360.391/a

BMJ 2002;325:391 ( 17 August )

Letters

Authors respond to criticism of rheumatoid arthritis twin study

The first 150 words of the full text of this article appear below.

EDITOR $---$ The letter by MacGregor et al in response to our twin study focuses on three points: heritability, bias, and the contributionof specific genes to the aetiology of rheumatoid arthritis.¹

MacGregor et al state that two previous twin studies on rheumatoid arthritis have reported comparable heritability estimatesat approximately 60%. But a heritability estimate is a theoreticalconcept relying on several assumptions which cannot at presentbe met in rheumatoid arthritis. Besides, heritability estimatesare population specific since the variation of environmental andgenetic effects may not be identical in different geographicalareas and ethnic populations.

(Credit: BARBARA SINGER/PHOTONICA)

In our study, twins younger than 42 were 92% of the total population, but an age adjusted estimate accords well with the latestpopulation based study from Norway in which the prevalence ofrheumatoid arthritis between 20 and 79 years was 0.437.² Prevalencesexceeding 1% were found only in people older than 60. Macgregoret al . . . [Full text of this article]