[1] It is associated with hypomorphic missense mutations in immunologically relevant genes of T-cells (and B-cells) such as recombination activating genes (RAG1 and RAG2), Interleukin-7 receptor-α (IL7Rα), DCLRE1C-Artemis, RMRP-CHH, DNA-Ligase IV, common gamma chain, WHN-FOXN1, ZAP-70 and complete DiGeorge syndrome.

This is because the patients have some T cells with limited levels of recombination with the mutant RAG genes.

[citation needed] A characteristic symptom is chronic inflammation of the skin, which appears as a red rash[2] (early onset erythroderma).

Other symptoms include eosinophilia, failure to thrive, swollen lymph nodes, swollen spleen, diarrhea, enlarged liver, low immunoglobulin levels (except immunoglobulin E, which is elevated), low T cell levels, and no B cells.

[4] Omenn syndrome can occasionally be caused in other recombination genes, including IL-7Rα and RMRP.