Monogenic autoinflammatory syndromes

What are monogenic autoinflammatory syndromes?

Monogenic autoinflammatory syndromes are inherited conditions caused by mutations in one or both copies of a single gene that result in over-activation of the innate immune system causing inappropriate inflammation. Importantly infection, allergies, immune deficiencies and autoimmune diseases must be excluded.

When the concept of autoinflammatory syndromes was first proposed in 1999, it was synonymous with hereditary periodic fever syndromes. However subsequent studies have uncovered the genetic cause of other conditions previously thought to be unrelated.

A monogenic condition means it is due to mutation(s) in a single gene.

The inheritance pattern can be used as an initial classification of the monogenic autoinflammatory syndromes. Some examples of these syndromes with dermatological manifestations are listed.

How do monogenic autoinflammatory syndromes present clinically?

Clinical clues that may suggest a monogenic autoinflammatory syndrome have been proposed by Gattorno et al.:

• Early onset
• Family history
• Chest and abdominal pain
• Diarrhoea
• Oral aphthous ulcers.

Most, but not all, present as recurrent attacks of fever with associated symptoms of inflammation often of joints, eyes and skin. Each syndrome has additional distinctive clinical features (see specific syndrome).

Many monogenic autoinflammatory syndromes have a major effect on the quality of life including significant disability and potentially life-threatening complications.

How are monogenic autoinflammatory syndromes diagnosed?

Diagnosis is primarily based on clinical features. Although these are genetic disorders, a family history of similar symptoms and signs is not always present, especially in those forms inherited as autosomal recessive.

Infections, allergy, malignancy, immunodeficiency and autoimmune disorders must be excluded on testing.

Some syndromes can be diagnosed on biochemical testing, such as a high level of mevalonic acid in urine during an attack of HIDS. Others show such a dramatic response to treatment that a trial of specific therapy confirms the clinical impression, for example, colchicine for familial Mediterranean fever.

Genetic testing is possible for most of these syndromes, although not always readily available or affordable. Mutations in the identified gene are not currently detectable in all sufferers. The test is therefore only helpful if a mutation is identified.

Where a gene mutation has been identified in the presenting patient (proband), genetic testing of family members may identify asymptomatic carriers who would benefit from treatment, for example, colchicine for familial Mediterranean fever to prevent the development of potentially fatal amyloidosis.

Prenatal diagnosis may also be considered for severe forms of monogenic autoinflammatory syndromes.

What is the treatment of monogenic autoinflammatory syndromes?

As these are genetic conditions, monogenic autoinflammatory syndromes cannot be cured. However many can be successfully controlled with specific therapy.

Familial Mediterranean fever shows a dramatic response to colchicine in the majority of sufferers, although the mechanism of effect is not yet known.

A number of these syndromes share the feature of interleukin-1-induced amplification of the innate immune system and therefore respond to blockade of this pathway using biologic agents such as anakinra. Anakinra is registered in several countries to treat rheumatoid arthritis.

DIRA is due to a specific deficiency of IL-1 receptor antagonist, which can be replaced by anakinra.