Omenn syndrome is an inherited disorder of the immune system (immunodeficiency). Omenn syndrome is one of several forms of severe combined immunodeficiency (SCID), a group of disorders that cause individuals to have virtually no immune protection from bacteria, viruses, and fungi. Individuals with SCID are prone to repeated and persistent infections that can be very serious or life-threatening. Infants with Omenn syndrome typically experience pneumonia and chronic diarrhea. Often the organisms that cause infection in people with this disorder are described as opportunistic because they ordinarily do not cause illness in healthy people.

Mutations in several genes involved in immune system function can cause Omenn syndrome. The two most frequent causes are mutations in the RAG1 and RAG2 genes. These genes provide instructions for making proteins that are active in two types of lymphocytes called B cells and T cells. To help fight infections, B cells and T cells have special proteins on their surface that help them recognize foreign invaders; these proteins must be somewhat different from each other to be able to recognize a wide variety of substances. The RAG1 and RAG2 proteins help increase the diversity of proteins that are on the surface of these cells.

Overall, the various forms of SCID are estimated to affect 1 in 75,000 to 100,000 newborns. The exact prevalence of Omenn syndrome is unknown.

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Published Date: February 01, 2017
Published By: National Institutes of Health