RESEARCH - A strong heritability of psoriatic arthritis over four generations - the Reykjavik Psoriatic Arthritis Study

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Rheumatology Advance Access originally published online on September 9, 2009

Rheumatology 2009 48(11):1424-1428; doi:10.1093/rheumatology/kep243

A strong heritability of psoriatic arthritis over four generations—the

Reykjavik Psoriatic Arthritis Study

Ari Karason1, Thorvardur Jon Love2,3 and Bjorn Gudbjornsson2,4

1deCODE Genetics, 2Centre for Rheumatology Research, Landspitali –

University Hospital, Reykjavik, Iceland, 3Brigham and Women's

Hospital, Harvard Medical School, Boston, USA and 4Faculty of

Medicine, University of Iceland, Reykjavik, Iceland.

Abstract

Objective. We have studied the prevalence of PsA in Reykjavik,

Iceland, in a population-based cohort, and using the Icelandic

genealogy database we have estimated the risk ratio (RR) spanning five

generations.

Methods. The national identification numbers of all 220 living

Icelanders in Reykjavik known to have PsA were linked with the

genealogy database. RRs for developing PsA were estimated in

first-degree relatives (FDRs) to fifth-degree relatives of PsA cases.

The kinship coefficient (KC) for PsA was also calculated. The control

populations were 1000 and 10 000 sets of matched Icelandic subjects

for each proband, respectively.

Results. FDRs to fourth-degree relatives of patients with PsA had RRs

of 39, 12, 3.6 and 2.3, respectively (all P-values < 0.0001),

reflecting a strong genetic component, whereas the fifth-degree

relatives had an RR of 1.2 (P = 0.236). KCs of 5.0, 3.4, 1.7, 1.3,

1.0, 0.8 and 0.7 were observed for the first seven excluded meioses

(all P-values < 0.0001), confirming the familial risk.

Conclusions. Patients with PsA in Reykjavik, Iceland, are

significantly more related to each other than to randomly sampled

control subjects. This is in agreement with previous reports, but the

present study examines the inheritance in more distantly related

individuals. These findings indicate that in addition to a strong and

complex genetic component in PsA, there is an important environmental

contribution.

http://rheumatology.oxfordjournals.org/cgi/content/abstract/48/11/1424?etoc

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