High prevalence of familial sarcoidosis in an Irish population.

Previous studies in the Republic of Ireland have demonstrated a high national prevalence of sarcoidosis. Observations in our sarcoid clinic suggested a high prevalence of the disease among siblings and prompted a survey to quantify this phenomenon. The study group comprised 114 index patients with biopsy proved sarcoidosis and a total sibling pool of 534 individuals. Eleven of the index patients (9.6%) were found to have at least one sibling with sarcoidosis. Of the 13 siblings thus identified, eight had biopsy proof of the disease, while the remaining five showed highly suggestive clinical and radiological evidence of sarcoidosis. There was no significant difference in the mode of presentation between the sibling pairs or between familial and non-familial cases and there was an equal distribution of like sex and unlike sex pairs. In only two instances was the temporal profile of onset of the disease suggestive of intrafamilial spread of a transmissible agent. The high prevalence of sarcoidosis among siblings reported here (2.4%) suggests that genetic factors significantly predispose to the development of sarcoidosis and that family members of affected patients should be screened for this disease.