In conclusion, LIG4 deficient patients may present soon after birth or later in life, with, or without: a family history of consanguinity and affected siblings, microcephaly, beaked nose, T-B-NK+ SCID, Omenn syndrome, low serum immunoglobulins, and very low B-cells, worsening pancytopenia, radiosensitivity; and they may develop bone marrow failure, sepsis, severe bleeding, and/or hematologic malignancies. This evidence concerns the gene LIG4 and Omenn syndrome.