Signs and symptoms of familial Mediterranean fever usually begin during childhood. They occur in bouts called attacks that last one to three days. Arthritic attacks may last for weeks or months.

Signs and symptoms of familial Mediterranean fever include:

• Fever
• Abdominal pain
• Chest pain
• Achy, swollen joints
• A red rash on your legs, especially below your knees
• Muscle aches
• A swollen, tender scrotum

Between attacks, you'll likely feel normal. Symptom-free periods may be as short as a few days or as long as several years.

Familial Mediterranean fever is caused by a gene mutation that's passed from parents to children. The gene mutation causes problems in regulating inflammation in the body.

In people with familial Mediterranean fever, the mutation occurs in a gene called MEFV. Many different mutations in MEFV are linked to familial Mediterranean fever. Some mutations may cause very severe cases, while others may result in milder signs and symptoms.

Factors that may increase the risk of familial Mediterranean fever include:

• Having a family history of the disease. If you have a family history of familial Mediterranean fever, your risk of the disease is increased.
• Being of Mediterranean ancestry. If your family can trace its history to the Mediterranean region, your risk of the disease may be increased. Familial Mediterranean fever can affect people in any ethnic group, but it may be more likely in people of North African, Jewish, Arab, Armenian, Turkish, Greek or Italian descent.

Complications can occur if familial Mediterranean fever isn't treated. Complications can include:

• Abnormal protein in the blood. During attacks of familial Mediterranean fever, your body may produce an abnormal protein (amyloid A). The protein can accumulate in your body and cause organ damage (amyloidosis).
• Kidney damage. Amyloidosis can damage the kidneys, causing nephrotic syndrome. Nephrotic syndrome occurs when your kidneys' filtering systems (glomeruli) are damaged. People with this condition may lose large amounts of protein in their urine. Nephrotic syndrome can lead to blood clots in your kidneys (renal vein thrombosis) or kidney failure.
• Infertility in women. Inflammation caused by familial Mediterranean fever may also affect the female reproductive organs, causing infertility.
• Joint pain. Arthritis is common in people with familial Mediterranean fever. The most commonly affected joints are the knees, ankles, hips and elbows.