Rheumatology Advance Access originally published online on April 30, 2003
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Rheumatology 2003; 42: 739-742
© 2003 British Society for Rheumatology
Genetic associations between frozen shoulder and tennis elbow: a female twin study
The Twin Research and Genetic Epidemiology Unit, St Thomas' Hospital, London SE1 7EH, UK
Objectives. To estimate the heritability of frozen shoulder (FS) and tennis elbow (TE) and to examine the two disorders for possible genetic or environmental associations.
Methods. Self-reporting questionnaire data on risk factors for, and a physician diagnosis of, FS or TE were obtained from 865 monozygotic (MZ) and 963 dizygotic (DZ) unselected female twin pairs aged between 20 and 76 yr registered with the St Thomas' UK Adult Twin Registry. The heritability of each disorder was estimated in a classic twin study. The association between FS and TE was then explored by log-linear modelling comparing MZ with DZ individuals and twin pairs for the presence of both disorders.
Results. The prevalence of FS and TE were 11.6 and 16.7%, respectively. A heritability of 42% was estimated for FS and 40% for TE after adjusting for age. There was no confounding by environmental risk factors. Log-linear modelling demonstrated FS and TE, independently, to be associated within members of a twin pair and confirmed a stronger association in MZ than DZ pairs. In addition the two disorders occurred together 23 times more frequently in individuals than would be expected by chance. However, there was no association between FS and TE across members of a twin pair, implying no evidence for a shared genetic component to the two disorders.
Conclusions. Genetic factors are implicated in the aetiology of both frozen shoulder and tennis elbow but are independent of each other. The two disorders occur together 23 times more frequently than by chance in individuals. However, the association is most likely mediated by individual-specific environmental factors common to the two conditions and not by a common genetic susceptibility.
KEY WORDS: Frozen shoulder, Tennis elbow, Tendonitis, Twins, Genetic epidemiology.
Correspondence to: A. J Hakim. E-mail: alan.hakim{at}whippsx.nhs.uk