Laboratory features

The laboratory picture is one of severe immune deficiency:

• serum immunoglobulins usually less than 1% of normal
• failure to produce antibodies in response to vaccinations such as DTP
• peripheral lymphocyte count less than 2000 per microlitre
• failure to mount a delayed-type hypersensitivity response to antigens
• absence of lymphocytes, plasma cells or lymphoid follicles in lymph nodes on biopsy
• 50 % of cases with the autosomal recessive form of SCID lack adenosine deaminase (ADA) in their lymphocytes and erythrocytes - results in accumulation of metabolites such as deoxyadenosine and deoxy-ATP and consequent toxicity to lymphocytes; these patients can be diagnosed prenatally by assaying the level of adenosine deaminase in the chorionic villi