Familial Mediterranean fever: prevalence, penetrance and genetic drift.

FMF is widely distributed in populations inhabiting the Mediterranean basin. It is mainly attributed to five founder mutations (M680I, M694V, M694I, V726A, E148Q) in the MEFV gene. The frequencies and distribution of these mutations in 146 FMF patients, of Arab and Jewish descent, were compared to that observed in 1173 healthy individuals of pertinent ethnic groups. Five mutations accounted for 91% of FMF chromosomes in our patients. Mutation M694V, predominant in North African Jews, was observed in all patients other than Ashkenazi Jews; mutation V726A was prevalent among all patients other than North African Jews; mutations M694I and M680I were mainly confined to Arab patients. Overall carrier rates, for four mutations (M680I, M694V, V726A, E148Q), were extremely high in our healthy cohort composed of Ashkenazi (n=407); Moroccan (n=243); Iraqi Jews (n=205); and Muslim Arabs (n=318); calculated at 1 : 4.5; 1 : 4.7; 1 : 3.5 and 1 : 4.3 respectively. The V726A allele prevalent among Ashkenazi and Iraqi Jews and Muslim Arabs (carrier rates: 7.4, 12.8 and 7.3%, respectively) was not found among Moroccan Jews. The M694V allele detected among Moroccan and Iraqi Jews and Muslim Arabs (carrier rates 11.1, 2.9 and 0.6%, respectively) was not observed among Ashkenazim. The overall frequency of mutations V726A and E148Q in Ashkenazim, Iraqi Jews and Arabs indicates that the bulk of individuals that comply with the genetic definition of FMF remain asymptomatic.