Immunoassay to Measure Ataxia-Telangiectasia Mutated Protein in Cellular Lysates

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Abstract
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 (≥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 ≤13%. Nuclear lysates from control LCLs and PBMCs had ATM protein concentrations of 49–610 μg/L and 48–943 μg/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 × 106 cells at concentrations of 64–463 μg/L and 42–444 μg/L for control LCLs and PBMCs, respectively. A-T heterozygotes had ATM protein concentrations of 52–98 μg/L. ATM protein was stable in PBMCs stored for 1 month at −70 °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.