The Omenn syndrome is a form of severe combined immune deficiency that is inherited autosomal recessively and characterized by growth retardation, erythrodermia, lymphadenopathy, hepatosplenomegaly and severe recurrent infections. Although circulating T lymphocytes on the lymphocyte panel are normal, their functions are abnormal. On the other hand, circulating B lymphocytes are decreased or absent. Our case was a baby girl who was born to the second pregnancy of a 29-year-old mother on the 37th gestational week. She had a history of a sister’s death on the 51st day of life due to Omenn syndrome. There was no consanguinity between parents. Her physical examination was normal expect generalized exfoliative erythrodermia. Routine laboratory investigations revealed eosinophilia. X-ray, echocardiography, abdominal and transfontanel ultrasonography findings were normal. IgG was at the lowest boundaries of the normal values. IgA and IgM were low as well. While T lymphocytes were elevated, B lymphocytes were extremely low. The family had a history of a baby death with the homozygote RAG1 g.854C>T (p.Q248X) mutation and parents were heterozygote carriers of the same mutation. Our patient also had the same homozygote RAG1 g.854C>T mutation. Since the parents’ immunoglobulin levels and lymphocyte panels were normal, haploidentical stem cell transplantation from the father was performed. Unfortunately our patient passed away due to pulmonary infection on the posttransplantation 12th day.Genetic counseling has a great significance as untreated Omenn syndrome is fatal but the disorder is treatable with appropriate bone marrow or umbilical cord blood stem cell transplantion

Keywords: Severe combined immune deficiency, Omenn syndrome