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Mutations in the ATM gene are responsible for the autosomal recessive disorder, ataxia telangiectasia (A-T). Mutations in different ethnic groups are distributed along the entire length of the large, 66 exon ATM gene. In this study, A-T patients from 16 Russian families were assessed for immunological status and ATM haplotype analysis, and screened for ATM mutations. Haplotype analysis was performed to enhance the efficiency of mutation detection. Mutations predicted to cause disease were identified in 19 of 32 alleles (59%), including a truncating mutation (c.5932G>T) that was identified in 8/32 (25%) alleles both by haplotype analysis and mutation screening. This mutation has been found in low abundance in other European A-T cohorts suggesting that this founder-effect mutation may be of Russian origin. The abundance of this mutation may allow for large-scale screening of cancer patients to help clarify the role of ATM in breast and other cancers. Nine of the remaining mutations were previously unreported, and add to the multitude of unique mutations found throughout the gene. © 2005 Wiley-Liss, Inc.

Mutations in ATM, the gene defective in the human genetic disorder ataxia-telangiectasia (A-T), have been described in A-T patients and in a variety of tumor samples. Most of these arise due to exon skipping. We developed an RT-PCR based protein truncation test (PTT) to screen for ATM mutations in breast cancer patients showing adverse response to radiotherapy. An additional PTT product was evident in the ATM gene in peripheral blood mononuclear cells (PBMCs) from blood samples that were collected 2 days or more prior to RNA extraction. Lymphoblastoid cell lines established from the same blood samples showed no evidence of the additional band. Cloning and sequencing of the additional RT-PCR product revealed an exact deletion of exon 20 (2639 del 200), pointing to exon skipping. RT-PCR analysis of RNA extracted from freshly prepared PBMCs from 3 normal individuals showed no evidence of the additional RT-PCR product but when the blood was stored for 2-3 days prior to RNA extraction the lower molecular weight band was evident in every sample. DNA sequencing confirmed this to be due to loss of exon 20. These data suggest that mRNA-based mutation analysis on ATM should be carried out on unstored blood samples to avoid artificial loss of exons that give rise to apparent mutations.