BOSTON — The occurrence of antineutrophil cytoplasmic antibody-associated vasculitis among close relatives of individuals with the condition is low, a Swedish study has shown. The findings provide insight into the long-unanswered question of genetic susceptibility of the autoimmune vasculitis, Dr. Ann Knight reported at the annual meeting of the American College of Rheumatology.
As with rheumatoid arthritis, the etiology of ANCA-associated vasculitis is thought to harbor some interplay between genetic predisposition and environmental triggers; however, little is known about whether the disease actually aggregates in families, said Dr. Knight of Uppsala University Hospital in Sweden. While familial clustering of ANCA-associated vasculitis has been reported in multiple case reports, “our results argue strongly against a pronounced increase in familial risk,” she said, noting that the degree of familial aggregation appears to be similar in magnitude to that observed in rheumatoid arthritis.
To assess familial risk of ANCA-associated vasculitis, Dr. Knight and colleagues conducted a population-based study of the Swedish Inpatient Register, a database of all patients admitted to Swedish hospitals since 1964 identifying 1,944 patients with ANCA-associated vasculitis for 1975-2004. Slightly more than half of the patients were male, and their mean age at first hospitalization was 61 years.
Through linkage to nationwide population-based Swedish registers on morbidity, family structure, and vital status, “we compared the occurrence of [ANCA-associated vasculitis] among the 6,670 first-degree relatives and 428 spouses of the [ANCA-associated vasculitis] patients to the occurrence of the disease among 68,994 first-degree relatives and 4,812 spouses of 19,655 randomly selected general population controls,” Dr. Knight explained. The investigators used the Cox proportional hazards regression method to estimate relative risks, taking potential familial clustering into account, she said.
Among the 6,670 relatives of ANCA-associated vasculitis patients, there were two cases of the disease (one pair, consisting of a mother and son), Dr. Knight reported. There were 13 cases among the first-degree relatives of the population controls, none of which occurred in the same family, she said. None of the spouses of patients were found to have the disease.
The relative risk of ANCA-associated vasculitis in first-degree relatives was 1.56, Dr. Knight stated. The low relative risk is of clinical relevance, she noted, because patients often ask whether their own diagnosis puts their closest relatives at increased risk for the disease. Previously, clinicians' ability to answer this question rested only on case reports, which by definition do not allow for risk quantification, she said.
Dr. Knight reported having no financial disclosures relative to her presentation.