Background: Familial aggregation of alopecia areata (AA) has been previously described, but systematic studies with information obtained directly from family members have yet to be undertaken.
Objective: We sought to study the pattern of familial aggregation of AA by assessing the affection status of patients' relatives. The study included 206 index patients with a total of 1029 first-degree and 2625 second-degree relatives.
Methods: First-degree relatives were directly interviewed, whereas information on second-degree relatives was obtained by interviewing the index patients and their first-degree relatives.
Results: Estimated lifetime risks were 7.1% in siblings, 7.8% in parents, and 5.7% in offspring. The risk in second-degree relatives was slightly higher than the reported population risk. Age at onset in index patients and first-degree relatives was significantly correlated.
Limitations: Using patients drawn from specialized hair clinics may have produced results showing a higher proportion of early onset and severe cases.
Conclusion: The familial aggregation of AA supports the role of genetic factors in the development of the disease. In addition, our data indicate genetic factors might contribute to the age at onset of AA.