Late-onset familial Mediterranean fever (FMF): a subset with distinct clinical, demographic, and molecular genetic characteristics.

To determine the prevalence and characterize demographic, clinical, and genetic features of familial Mediterranean fever (FMF) of late onset, all patients experiencing their first FMF attack at age 40 years or more were identified using the computerized registry of our FMF clinic, and then thoroughly interviewed and examined. The control group consisted of 40 consecutive FMF patients, who arrived at the FMF clinic for their regular follow-up visit and were 40 years of age or older at the time of the examination. The severity of the disease in patients and controls was determined using a modified score, developed previously. Mutational analysis in the FMF gene was performed using a commercial kit. Only 20 of 4000 (0.5%) patients had late-onset FMF. These patients were mostly men, of non-North African origin, P < 0.05 compared to controls. All had abdominal attacks and in most these were the only manifestation of their disease, P < 0.001. None had chronic or prolonged manifestations of FMF, for example, amyloidosis, chronic arthritis, or protracted myalgia, P < 0.001. The response to treatment was good despite using low colchicine dose, P < 0.05. The overall severity score indicated a mild disease, P < 0.001. Mutational analysis revealed absence of M694V homozygosity, P < 0.01, compared to our regular FMF population. We conclude that the onset of FMF in a late age defines a milder form of disease with typical clinical, demographic, and molecular genetic characteristics.