Adenosine Deaminase Severe Combined Immunodeficiency (ADA-SCID) is a rare, autosomal recessive disorder of purine metabolism characterized by immunodeficiency, failure to thrive and metabolic abnormalities. A lack of the enzyme ADA allows accumulation of toxic metabolites causing defects of both T cell and B cell mediated and humoral immunity.
ADA-SCID occurs in one in 200,000 to 1,000,000 newborns worldwide, accounts for about 15 percent of all cases of severe combined immunodeficiency (SCID).1 ADA deficiency may be present in infancy, childhood, adolescence, or adulthood. Individuals with ADA-SCID lack immune protection from bacteria, viruses, and fungi, putting them at increased risk of severe and recurring infections caused by opportunistic organisms that ordinarily do not lead to illness in people with normally functioning immune systems. The most common symptoms of ADA-SCID are pneumonia, chronic diarrhea, and skin rashes. Additionally, children with ADA-SCID grow more slowly than healthy children, and some have developmental delays.1-4 ADA-SCID is typically diagnosed within the first six months of life; left untreated, babies with ADA-SCID usually die before they reach age 2 unless they are diagnosed early and effective treatment is started.3-4
Patients of ADA-SCID have mutations on chromosome 20 as it is where the highly conservative ADA gene located. ADA-SCID can be treated by either stem cell transplant, or gene therapy or enzyme replacement therapy.
Some of the states in the US require routine screening for SCID (including ADA-SCID) in newborns. The Advisory Committee on Heritable Disorders in Newborns and Children has recommended routine newborn screening for SCID and will be determining whether national screening should be mandatory.5-7 Use of the newer technology known as TREC (T-cell Receptor Excision Circles) can be done at birth to identify babies with SCID and intervene with supportive care. Babies found to be positive can have assays (enzyme tests) for ADA to identify babies with ADA deficiency before symptoms or illness develop.7