RESEARCH - On the heritability of psoriatic arthritis: disease concordance among monozygotic and dizygotic twins

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Ann Rheum Dis. Published Online First: 24 January 2008.

doi:10.1136/ard.2007.078428

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Extended Report

On the heritability of psoriatic arthritis. Disease concordance among

monozygotic and dizygotic twins

Ole Birger Pedersen 1*, Anders Jørgen Svendsen 2, Leif Ejstrup 1, Axel

Skytthe 3 and Junker 1

1 Department of Rheumatology, Odense University Hospital, Denmark

2 Institute of Public Health, University of Southern Denmark, Denmark

3 The Danish Twin Registry, Institute of Public Health, University of

Southern Denmark, Denmark

Abstract

Objective: In a nationwide unselected twin population to estimate the

relative importance of genetic and environmental effectors in the

etiopathogenesis of psoriatic arthritis (PsA).

Methods: The study comprised three Danish nationwide twin cohorts. In

1994 and 2002 a total of 37,388 and 46,418 Danish twin individuals

respectively were asked by questionnaire if they had PsA. Twins

reporting PsA were invited to participate in a clinical examination.

Patients were classified according to the Moll and (M & W) and

the CASPAR criteria. Heritability was estimated by probandwise

concordance rates and variance component analysis.

Results: 228 twin individuals reported PsA. Following diagnostic

validation in 184 (81%), 50 probands were diagnosed with PsA according

to the M & W criteria. Five of their co-twins were either dead, had

emigrated, or did not participate in the twin study and nine did not

respond, resulting in 36 complete pairs. A total of 1/10 MZ pairs and

1/26 DZ pairs were concordant for PsA, yielding a 6.2% difference in

proportions (95% CI: -11%, 37%). 5/10 MZ pairs and 4/26 DZ pairs were

concordant for psoriatic skin disease implying a 35% difference (95%

CI: 2%, 60%, p < 0.05).

Conclusion: This first twin study on PsA confirms that genes are

important in the causation of psoriatic skin disease. Despite the

limited statistical power, the almost identical concordance rates for

PsA in MZ and DZ twins stresses the importance of continued search for

non genetic effectors in PsA.

http://ard.bmj.com/cgi/content/abstract/ard.2007.078428

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