Adenosine deaminase deficiency with normal immune function. An acidic enzyme mutation.

Abstract

A B S T R A C T In most instances, marked deficiency of the purine catabolic enzyme adenosine deaminase results in lymphopenia and severe combined immunodeficiency disease. Over a 2-yr period, we studied a white male child with markedly deficient erythrocyte and lymphocyte adenosine deaminase activity and normal immune function. We have documented that (a) adenosine deaminase activity and immunoreactive protein are undetectable in erythrocytes, 0.9% of normal in lymphocytes, 4% in cultured lymphoblasts, and 14% in skin fibroblasts; (b) plasma adenosine and deoxyadenosine levels are undetectable and deoxy ATP levels are only slightly elevated in lymphocytes and in erythrocytes; (c) no defect in deoxyadenosine metabolism is present in the proband's cultured lymphoblasts; (d) lymphoblast adenosine deaminase has normal enzyme kinetics, absolute specific activity, S20,w, pH optimum, and heat stability; and (e) the proband's adenosine deaminase exhibits a normal apparent subunit molecular weight but an abnormal isoelectric pH. In contrast to the three other adenosine deaminase-deficient healthy subjects who have been described, the proband is unique in demonstrating an acidic, heat-stable protein mutation of the enzyme that is associated with <1% lymphocyte adenosine deaminase activity. Residual adenosine deaminase activity in tissues other than lymphocytes may suffice to metabolize the otherwise lymphotoxic enzyme substrate(s) and account for the preservation of normal immune function.Dr. Mitchell is the recipient of a scholar award from the Leukemia Society of America.

Paradoxical expression of adenosine deaminase in T cells cultured from a patient with adenosine deaminase deficiency and combine immunodeficiency.

“…About 10 healthy individuals, identified through screening, have had normal immune function (4)(5)(6)(7)(8)(9)(10)(11)(12). Both groups lack ADA activity in erythrocytes, but whereas the former also has .…”

“…Both groups lack ADA activity in erythrocytes, but whereas the former also has . 1% of normal activity in blood mononuclear cells and B cell lines (complete deficiency) (6,9,10,13), the latter has 4-70% of normal activity (partial deficiency). Structural gene mutations, which presumably diminish enzyme stability or catalytic activity to different extents, occur in both groups (14)(15)(16)(17)(18)(19)(20)(21).…”

Transient expression of human adenosine deaminase cDNAs: identification of a nonfunctional clone resulting from a single amino acid substitution.

“…Although the deficiency is genetically heterogeneous, most patients have virtually no detectable enzyme activity and variable, or little, immunoreactive protein in their erythrocytes and residual lymphocytes (3,5,7,16,33,40). These findings suggest that severe ADA deficiency arises from structural mutations affecting enzyme activity and stability.…”

“…Immunoreactive ADA protein was determined by Western blot analysis as previously described (7) except second antibody, goat anti-rabbit horseradish peroxidase, and 4-chloro-1-napthol were used for color development and detection (15).…”

“…After transfection into cultured monkey kidney COS cells (13), pSV2 recombinants were amplified, and the cDNA inserts were transcribed from the SV40 early region promoter. Forty-eight hours after transfection, COS cells were harvested and assayed both for ADA enzyme activity by in situ assay in starch gels (31) and polyacrylamide gels (18) as well as quantitative assay (7) and for ADA mRNA sequences by slot blot hybridization and Si nuclease mapping (10).…”