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Immunoassay to measure ataxia-telangiectasia mutated protein in cellular lysates
Anthony W Butch1, Helen H Chun, Shareef A Nahas
1Department of Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California-Los Angeles, Los Angeles, CA 90095, USA. abutch@mednet.ucla.edu
Background:
Ataxia-telangiectasia (A-T) is a neurologic disorder caused by mutations in the ataxia-telangiectasia mutated (ATM) gene. A clinical diagnosis of A-T is confirmed by radiosensitivity testing and immunoblotting for ATM protein. Because both of these tests have long turnaround times (> or =3 months), we developed a rapid immunoassay to measure ATM protein and determined its sensitivity and specificity for diagnosing A-T.
Methods:
Recombinant ATM protein was used for standardization. Lysates of lymphoblastoid cell lines (LCLs) and peripheral blood mononuclear cells (PBMCs) from A-T patients, controls, and A-T heterozygotes were tested for ATM protein by immunoassay.
Results:
Between-run imprecision (CV) was < or =13%. Nuclear lysates from control LCLs and PBMCs had ATM protein concentrations of 49-610 microg/L and 48-943 microg/L, respectively. ATM protein was not detectable in LCL nuclear lysates from 18 of 21 A-T patients. The three remaining A-T patients had trace amounts of ATM protein, which was confirmed on immuoblots. ATM protein was also detectable in whole-cell lysates from 4 x 10(6) cells at concentrations of 64-463 microg/L and 42-444 microg/L for control LCLs and PBMCs, respectively. A-T heterozygotes had ATM protein concentrations of 52-98 microg/L. ATM protein was stable in PBMCs stored for 1 month at -70 degrees C, but rapidly decreased after 1 day in unprocessed blood.
Conclusions:
This ATM protein immunoassay can be used to confirm a diagnosis of A-T in 2 days on small numbers of PBMCs and can potentially identify A-T carriers and individuals at increased risk for cancer.
