Objectives: To determine the recurrence risk of psoriatic arthritis (PsA) and uncomplicated psoriasis in first degree relatives (FDRs) of patients with PsA.
Methods: All available FDRs (full siblings, parents, and children) of 100 consecutive consenting patients attending a PsA clinic were evaluated for the presence of psoriasis and PsA using a standard protocol. The protocol included a screening questionnaire, physical examination by a rheumatologist, radiographic and laboratory assessment. Prevalence of PsA and Ps in FDRs of index case was determined and recurrence risk ratio λ was calculated, assuming a population prevalence of PsA of 0.25%, and population prevalence of Ps of 2%.
Results: The 100 probands had 533 relatives. Eighty four of them were deceased and 53 were unavailable (age <16 years). Of the remaining 396 FDRs, 107 did not participate (living too far away/did not consent). Thus, 289/396 (73%) of the available FDRs participated in the study. There were 130 siblings, 108 parents and 51 children. The prevalence of PsA and psoriasis among FDRs was 7.6% and 15.2%, respectively. The λ1 was 30.4 for PsA and 7.6 for Ps. The prevalence of PsA and psoriasis in siblings was 7.7% and 17.7%, respectively. The λS was 30.8 for PsA and 8.8 for Ps.
Conclusions: The recurrence risk ratio for both PsA and psoriasis is high in FDRs and siblings of patients with PsA. These results confirm that both PsA and psoriasis have a strong heritable component.