What is the role of lab tests in the workup of ataxia-telangiectasia (A-T)?

Updated: Apr 06, 2020
  • Author: Camila K Janniger, MD; Chief Editor: Dirk M Elston, MD  more...
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Laboratory markers are important for both diagnosis and prognosis. The most constant markers are elevated levels of alpha-fetoprotein (AFP) and carcinoembryonic antigen and chromosomal abnormalities, especially inversions and translocations involving chromosomes 7 and 14, though neither of these abnormalities is always found and their demonstration requires specific techniques available in only a few centers.

The demonstration of humoral or cellular immunologic defects may also permit an early diagnosis, although such defects are nonspecific and present less frequently.

The dysgammaglobulinemia of ataxia-telangiectasia includes an absent or low level of immunoglobulin A (IgA), including secretory IgA; a normal or low level of immunoglobulin G (IgG); and an elevated or normal level of immunoglobulin M (IgM). Elevated IgM is evident in only 60% of patients. [7] IgA deficiency is found in about 70% of patients with ataxia-telangiectasia syndrome. A deficit in IgG2 and IgG4 subclasses has been demonstrated in several patients, and IgE may also be absent or low.

Defects of cellular immunity include a low lymphocyte count, a poor response to skin tests to common antigens, low T-lymphocyte proliferation in the presence of mitogens, and deficient antibody production to viral or bacterial antigens. Excessive T-cell suppressor activity and intrinsic B-cell defects have been described in some patients, suggesting disturbances of immunoregulatory mechanisms. The incidence of immunologic abnormalities increases with the age of the patients.

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