SAIDs occur due to a defect in the immune system. This may be due to a genetic mutation, or there may not be a clear cause. Environmental factors can trigger the reaction in some people.

Your immune system protects you by detecting and fighting harmful substances in the body. These include bacteria, viruses, fungi, chemicals, toxins and foreign particles (such as a splinter).

Your immune system involves:

• Innate immunity — this is the protection you are born with. Innate immunity involves barriers that prevent harmful materials from entering your body. Examples include your skin, stomach acid and mucus. This is the first line of defense against attackers.
• Adaptive immunity — this is the protection you get when your body learns over time which substances are harmful. Your immune system builds up a defense against the specific substance. Vaccines work by training your adaptive immunity to recognize and attack harmful invaders, such as the flu virus.

SAIDs occur due to an abnormal response of innate immunity. Autoimmune diseases occur due to an abnormal response of adaptive immunity.

When innate immunity is activated, it triggers your immune response. Certain chemicals in the body are released at the site of infection or injury and cause signs of inflammation, including redness, warmth, pain and swelling. Inflammation is part of the body’s self-healing process. When you recover from your illness or injury, the inflammation goes away.

SAIDs occur when innate immunity is activated without a clear cause. This can cause inflammation to occur in excess or to last for long periods. Excessive inflammation can damage healthy tissue in the skin, bones, eyes, liver, heart or kidneys.

The defective MEFV gene responsible for the most common autoinflammatory disease, familial Mediterranean fever (FMF), was first identified in 1997. Since then, many SAIDs have been identified. Not everyone has a clear genetic cause.

There are more than 50 SAIDs, including:

• Familial Mediterranean fever (FMF)
• Tumor necrosis factor receptor-associated periodic syndrome (TRAPS)
• Cryopyrin-associated periodic syndromes (CAPS)
• Hyperimmunoglobulinemia D with intermittent fever syndrome (HIDS)
• Aicardi-Goutière syndrome
• Blau syndrome
• Adult Still disease
• Hereditary angioedema
• Behçet’s disease

Each SAID affects people differently. Some occur for a few years and never return. Some last a lifetime and need ongoing management.

SAIDs can be passed down in families. So if your parents or siblings have an SAID, you are more likely to develop it as well.