Severe combined immune deficiency in an adenosine deaminase-deficient patient

A case of adenosine deaminase (ADA) deficiency is described briefly. The clinical characteristics, pathogenesis, diagnosis, and management of this disease are discussed, followed by clinical pearls and pitfalls. ADA deficiency was identified in 1972 as a cause of severe combined immunodeficiency (SCID) and its incidence is approximately 1/10(6). This defect accounts for approximately 17% of all SCIDs and 50% of all autosomal recessive SCIDs. The patients typically have impaired immune function with recurrent severe infections, diarrhea, and failure to thrive. Because death occurs within a few months if untreated, it is a medical emergency. There are certain distinguishing features of ADA deficiency, including multiple skeletal abnormalities of chondro-osseous dysplasia on radiographic examination. ADA deficiency causes profound lymphopenia with all cells lines affected and is known as the T-B-NK-SCID type. The diagnosis of ADA deficiency requires measurements of plasma ADA and of deoxyadenosine metabolites. More than 67 mutations have been described, with 41 being missense mutations, which are more deleterious. The metabolic basis of the immunodeficiency is likely related to the sensitivity of lymphocytes to the accumulation of the aberrant ADA substrates, e.g., adenosine and 2'-deoxyadenosine. Intravenous immunoglobulin and antibiotics prophylaxis remains the mainstay of treatment with stem cell transplant being the initial management of choice.