Familial Mediterranean fever (FMF) is also called recurrent polyserositis. The salient features of FMF include brief recurrent episodes of peritonitis, pleuritis, and arthritis, usually with accompanying fever. As the name indicates, FMF occurs within families and is much more common in individuals of Mediterranean descent than in persons of any other ethnicity. Nonsense or missense mutations in the MEFV (Mediterranean fever) gene appear to cause the disease in many cases. MEFV produces a protein called pyrin (derived from the association with predominant fever) or marenostrin (derived from the phrase "our sea," because of the Mediterranean heritage of most patients).
The protein is expressed mostly in neutrophils. Its exact function is unknown, but it may function as an inhibitor of chemotactic factor (C5a) or perhaps of interleukin (IL)–8. Individuals with normal pyrin/marenostrin levels may have the ability to deactivate the target chemotactic factor when it is produced in response to an inflammatory stimulus. However, patients with FMF lack this ability, resulting in uninhibited activity of the chemotactic factor and episodes of inflammation (with accompanying fever) in the peritoneum, pleura, and joints. Presumably, these inflammatory episodes lead to the excess production of amyloid A protein from the acute phase and reactant serum amyloid A with subsequent deposition in the kidneys; however, only patients with specific MEFV haplotypes develop amyloidosis.
The frequency of FMF in any location depends on the ethnic background of the population. In Ashkenazi Jewish people (descended from Eastern European Jewish people and including most European and American Jewish people), the prevalence of FMF is 1 case per 73,000 population, with a MEFV gene frequency now estimated at perhaps 1 per 5, in contrast to previous estimates of 1 per 135. In Sephardic Jewish people (descended from Jewish people who were expelled from Spain, largely to North Africa, and including other Middle Eastern Jewish populations), the prevalence of FMF is 1 case per 250-1000 population, with a gene frequency of 1 per 8-16. Approximately one third of female patients with FMF are infertile, and 20-30% of pregnancies result in fetal loss. In adults, FMF is more prevalent in men than in women, with a male-to-female ratio of 1.5-2:1. Of all persons with FMF, 50-60% are younger than 10 years, 80-95% are younger than 20 years, and 5-10% are older than 20 years at onset. Onset in persons older than 40 years is rare.
The main symptoms of Familial Mediterranean Fever are recurrent episodes of fever, accompanied by abdominal, chest or joint pain. Not all children will have all the symptoms, and symptoms may change over time. Episodes usually last 1 – 3 days and go away without treatment. Most children look and feel healthy between episodes, but some children have such frequent episodes they do not fully recover or do not grow properly. Joint pain may accompany the episodes of fever. Usually, only one joint is affected at a time, most commonly an ankle or a knee. The joint may be so swollen and painful that the child cannot walk. One-third of patients may have a red rash over the lower extremities, usually near the ankles and feet. In some children, the only finding of the disease may be episodes of joint pain and swelling, which can be misdiagnosed as acute rheumatic fever or juvenile idiopathic arthritis. At present, there is no known cure for Familial Mediterranean Fever (FMF). Physicians can only treat the symptoms of the disease.
A common therapy for FMF is daily use of the drug colchicine, a medicine that reduces inflammation. This therapy has been successful in preventing attacks of fever in 75 percent of patients who take the drug regularly, and over 90 percent of patients demonstrate a marked improvement. Even if colchicine does not prevent the fever attacks, it does prevent the amyloidosis. However, compliance in taking colchicine every day is very important. If a patient stops taking the drug, an attack can occur within a couple of days. Since the gene that causes FMF codes for the protein pyrin, researchers hope that by studying how this protein works they will ultimately develop improved treatments for FMF, and possibly for other conditions involving excess inflammation.