Familial Mediterranean Fever (FMF) is the most common of all the known autoinflamatory diseases. There is a genetic test for the FMF gene mutation (MEFV). The FMF genetic mutation has a protein that helps to code the pyrin protein, that is similar to the pyrin domain for MWS, FCAS and NOMID/CINCA, but it is of a different genetic origin. FMF is much more common that FCAS, MWS, or NOMID/CINCA as well.
The genetic mutation or FMF is autosomal recessive, meaning that you must inherit mutated genes from both parents that carry the mutation to cause a person to have FMF. Carriers of the recessive gene may not be symptomatic, in most cases. But there are a few recent studies that indicate that in some patients, symptoms of FMF can be present even if the person has inherited the FMF mutation from only one parent, so more research is needed.
People of Jewish, Armenian, Arab, Turkish, Mediterranean, or Middle Eastern decent are the most common carriers of this hereditary periodic fever syndrome. It is estimated that 1 out of every 5-7 people in the affected ethnic groups listed above may be carriers of the FMF gene, and 1 out of every 200 people from these ethnic groups may have this disease. There are a number of known mutations causing FMF, but the most common is M694V.
Familial Mediterranean Fever (FMF) often presents with longer episodes of fever, and FMF can cause arthritis (especially in the ankles), along with many other symptoms. Gastrointestinal pain is common during flare episodes, due to inflammation in the abdominal cavity (peritonitis). Inflammation in the lung cavity (Pleurisy) and even pericardial effusions or pericarditis (inflammation around the heart) are also noted during FMF disease flares in many patients. Ersipeloid erythema is often seen during flares on the ankle-foot-below knee region in FMF. Many FMF patients also develop amyloidosis, whereas only 25% of MWS patients and others with CAPS develop full amyloidosis. Symptoms usually begin in most patients between preschool and adolescence, but this disease is present throughout the patient's life. C-reactive protein, Erythrocyte Sedimentation Rate (ESR), a Complete Blood Count (CBC) with a White Blood Count (WBC) and serum Amyoid evaluation can be helpful for diagnosing, and monitoring treatment in patients with FMF.
Of note: There a number of cases of NOMID/CINCA and TRAPS patients having had pericardial effusions as well, so testing for other periodic fever syndromes should be taken into consideration if a patient has pericardial effusions, and does not "fit" the classification of FMF.