Familial aggregation of psoriatic arthritis

The aim of this study was to determine the recurrence risk of psoriatic arthritis (PsA) and uncomplicated psoriasis in first-degree relatives (FDRs) of patients with PsA.

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, and radiographic and laboratory assessment. The prevalence of PsA and psoriasis in FDRs of the index cases was determined, and the recurrence risk ratio (lambda) was calculated, assuming a population prevalence of PsA of 0.25%, and a population prevalence of psoriasis of 2%.

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 lambda(1 )was 30.4 for PsA and 7.6 for psoriasis. The prevalence of PsA and psoriasis in siblings was 7.7% and 17.7%, respectively. The lambda(S) was 30.8 for PsA and 8.8 for psoriasis.

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.