What is Omenn Syndrome?
Doctors have long recognized that some infants will present with features of classical SCID (for example, serious bacterial, viral, or fungal infections, often involving the lungs resulting in trouble breathing or the gastrointestinal tract causing diarrhea and weight loss – features that suggest the immune system is not working properly), but also with other features that suggest the immune system is overacting (working too well). Infants with Omenn syndrome have features that suggest the immune system is not working, and on the other hand, also overacting, all at the same time.
Features that suggest the immune system is overacting include (1) a severe skin rash that often covers most of the body (sometimes called “generalized erythroderma” or “pachydermatitis”). This can look like a bad sunburn. Often infants with Omenn syndrome do not have hair or eyebrows because of this severe skin rash. (2) Enlarged lymph nodes (glands that can be felt in the neck, armpits, and groin) (3) Enlarged liver and spleen (organs found inside the abdomen). The liver and spleen should normally be under the rib cage and difficult to feel, but when enlarged, can be felt by the doctor during an abdominal examination. Some infants with Omenn Syndrome will have all of these features, whereas others will only have some of them.
Is Omenn Syndrome a diagnosis?
Yes, in that it describes an infant with severe combined immune deficiency who also has features of an overacting immune system. In all cases, however, Omenn Syndrome has an underlying cause. There are a number of potential underlying causes of Omenn Syndrome, however, only about 50% of the time are doctors able to figure out what this cause is. If no underlying cause can be found, the patient is diagnosed with Omenn Syndrome. If an underlying cause is found, the patient is diagnosed with Omenn Syndrome due to whatever the cause is.
What causes Omenn Syndrome?
A number of genetic mutations that also cause classical severe combined immune deficiency have also been found in Omenn Syndrome. These include RAG1, RAG2, adenosine deaminase deficiency, ARTEMIS, and DNA Ligase IV (and this list is not complete). Other disorders that have been associated with Omenn Syndrome include cartilage hair hypoplasia (short, hair abnormalities, skeletal abnormalities), CHARGE syndrome (coloboma of the eye, heart defects, atresia of the choanae, retardation of growth and/or development, genital abnormalities, ear abnormalities including deafness) and DiGeorge syndrome (low calcium, low parathyroid hormone levels, heart defects). Your doctor will look for other problems that may help to explain why Omenn syndrome has developed.