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Omenn syndrome
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Omenn syndrome

Omenn syndrome is a severe, inherited immunodeficiency disorder characterized by a lack of immune protection and an autoimmune reaction that attacks the body's own tissues.

Overview

Omenn syndrome is a form of severe combined immunodeficiency (SCID). Individuals with this condition have virtually no immune protection from bacteria, viruses, and fungi, making them prone to repeated, life-threatening infections. Infants typically experience pneumonia and chronic diarrhea.

In addition to immunodeficiency, children develop autoimmunity, where the immune system attacks the body's own tissues. Features include:

  • Very red skin (erythroderma)
  • Hair loss (alopecia)
  • Enlarged liver and spleen (hepatosplenomegaly)
  • Enlargement of the thymus and lymph nodes

Without treatment to restore immune function, children with Omenn syndrome usually survive only until age 1 or 2.

Causes

Omenn syndrome is caused by mutations in several genes involved in immune function, most frequently the RAG1 and RAG2 genes. These genes provide instructions for proteins active in B cells and T cells (types of lymphocytes). These proteins help increase the diversity of surface proteins on lymphocytes, which allows the immune system to recognize a wide variety of foreign invaders.

Mutations in RAG1 and RAG2 drastically reduce protein function, severely limiting the diversity of B and T cells. While the number of T cells may be normal, they are highly similar and abnormal, leading them to attack the body's own cells and tissues, which accounts for the autoimmune features of the syndrome.

Inheritance

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

Frequently Asked Questions

Survival rates exceed 80 % with matched sibling or unrelated donor transplants performed early (before 3–4 months of age). Most survivors achieve normal immune function, but they remain at risk for graft‑versus‑host disease, infections, and may need lifelong monitoring of immune reconstitution.
Diagnosis relies on a combination of clinical features (erythroderma, hepatosplenomegaly, chronic diarrhea), laboratory findings (very low or absent B‑cell numbers, oligoclonal but activated T‑cells, elevated IgE), and genetic testing confirming biallelic RAG1/2 or other SCID‑related mutations.
Carriers (heterozygous parents) are typically asymptomatic because one functional copy provides enough enzyme activity. However, each pregnancy carries a 25 % chance of an affected child if both parents are carriers, so carrier testing and genetic counseling are recommended.
The child requires isolation to prevent infections, broad‑spectrum antimicrobial prophylaxis, intravenous immunoglobulin (IVIG) to provide passive immunity, and aggressive control of the autoimmune skin and gut inflammation with steroids or other immunosuppressants. Definitive therapy is hematopoietic stem cell transplantation (HSCT) as soon as a suitable donor is identified.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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