Pleuritis occurs in 40% of patients and makes it difficult to breathe or lie flat, but pericarditis is rare. Scrotal attacks due to inflammation of the tunica vaginalis are somewhat rare but may be mistaken for testicular torsion. Myalgia (rare in isolation)
Erysipeloid rashes (a skin reaction on the legs that can mimic cellulitis, rare in isolation)

Complications
AA-amyloidosis with kidney failure is a complication and may develop without overt crises. AA amyloid protein is produced in very large quantities during attacks, and at a low rate between them, and accumulates mainly in the kidney, as well as the heart, spleen, gastrointestinal tract, and thyroid.There appears to be an increase in the risk for developing particular vasculitis-related diseases (e.g. Henoch–Schönlein purpura), spondylarthropathy, prolonged arthritis of certain joints and protracted myalgia. Genetics
The MEFV gene is located on the short arm of chromosome 16 (16p13). Many different mutations of the MEFV gene can cause the disorder. Having one mutation is unlikely to cause the condition. Having two mutations either a copy from both parents, or two different mutations, one from each parent is the threshold for a genetic diagnosis of FMF. However, most individuals who comply with the genetic diagnosis of FMF remain asymptomatic or undiagnosed. Whether this is due to modifier genes or environmental factors remains to be established. Pathophysiology
Virtually all cases are due to a mutation in the Mediterranean Fever (MEFV) gene on the chromosome 16, which codes for a protein called pyrin or marenostrin.
Familial Mediterranean fever (FMF) is a hereditary inflammatory disorder. : 149   FMF is an autoinflammatory disease caused by mutations in Mediterranean fever gene, which encodes a 781–amino acid protein called pyrin. While all ethnic groups are susceptible to FMF, it usually occurs in people of Mediterranean origin—including Sephardic Jews, Mizrahi Jews, Ashkenazi Jews, Assyrians, Armenians, Azerbaijanis, Levantines, Kurds, Greeks, Turks and Italians.The disorder has been given various names, including familial paroxysmal polyserositis, periodic peritonitis, recurrent polyserositis, benign paroxysmal peritonitis, periodic disease or periodic fever, Reimann periodic disease or Reimann syndrome, Siegal-Cattan-Mamou disease, and Wolff periodic disease. Note that "periodic fever" can also refer to any of the periodic fever syndromes. Signs and symptoms
Attacks
There are seven types of attacks. Ninety percent of all patients have their first attack before they are 18 years old. All develop over 2–4 hours and last anywhere from 6 hours to 5 days. Most attacks involve fever. Abdominal attacks, featuring abdominal pain, affect the whole abdomen with all signs of peritonitis (inflammation of abdominal lining), and acute abdominal pain like appendicitis. They occur in 95% of all patients and may lead to unnecessary laparotomy. Incomplete attacks, with local tenderness and normal blood tests, have been reported. Joint attacks mainly occur in large joints, especially in the legs. Usually, only one joint is affected. 75% of all FMF patients experience joint attacks. Chest attacks include pleuritis (inflammation of the pleura) and pericarditis (inflammation of the pericardium).