This autosomal recessive disease is caused by hypomorphic mutations that impair LIG4 function leading to deficient DNA damage repair mechanisms, and it is classified in the group of immunodeficiencies affecting cellular and humoral immunity, specifically T-B- Severe Combined Immunodeficiency (SCID), according to the 2024 Update on the Classification of Human Inborn Errors of Immunity (8, 13, 14). This evidence concerns the gene LIG4 and severe combined immunodeficiency.