Adenosine deaminase deficiency

Adenosine deaminase (ADA) deficiency accounts for about half of the autosomal recessive forms of SCIDs. ADA follows PNP in purine nucleoside catabolism, but deficiency in this enzyme causes even more severe symptoms than PNP deficiency, which is a T cell deficiency. ADA degrades toxic adenosine and deoxyadenosine, which accumulate in the cells of patients. Immature lymphoid cells are particularly sensitive to these nucleotides. In addition to immunological defect, most patients with ADA deficiency also have skeletal abnormalities.

Alternative names

Adenosine aminohydrolase, Severe combined immunodeficiency due to adenosine deaminase deficiency

SCID Due to ADA deficiency



  • Combined B and T cell immunodeficiencies
    • Deficiencies of purine metabolism


Autosomal recessive


#202500 Severe combined immunodeficiency 1, SCID1

+102700 Adenosine deaminase; ADA

Cross references

Phenotypically related immunodeficiencies

IDR factfile for PNP deficiency


1/2 x 100 to 1 x 100 births.