Michael Swift

Molecular genotyping shows that ataxia-telangiectasia heterozygotes are predisposed to breast cancer.

About 1.4% of the general population are heterozygous carriers of the gene for ataxiatelangiectasia (A-T), an autosomal recessive progressive neurologic syndrome in which cancer incidence of homozygotes is approximately 100-fold greater than the general populations rates. The hypothesis that A-T heterozygotes are predisposed to breast cancer was tested by the unbiased statistically powerful index-test method based on molecular genotyping. The A-T gene carrier status of 775 blood relatives in 99 A-T families was determined by tracing the A-T gene in each family through tightly linked flanking DNA markers. There were 33 women with breast cancer who could be genotyped; 25 of these were A-T heterozygotes, compared to an expected 14.9 (odds ratio 3.8, 95% confidence limits 1.7-8.4, one-sided p = .0001). This demonstrates that the A-T gene predisposes heterozygotes to breast cancer. For the 21 breast cancers with onset before age 60, the odds ratio was 2.9 (1.1-7.6, p = .009) and for the 12 cases with onset at age 60 or older, the odds ratio was 6.4 (1.4-28.8, p = .002). Thus the breast cancer risk for A-T heterozygous women is not limited to young women but appears even higher at older ages. Of all breast cancers in the United States, 6.6% may occur in women who are A-T heterozygotes. This proportion is several fold greater than the estimated proportion of carriers of BRCA1 mutations in breast cancer cases with onset at any age.

Treatment of lymphoid malignancies in patients with ataxia-telangiectasia.

BACKGROUND Patients with ataxia-telangiectasia (A-T) are at an increased risk for developing lymphoid malignancies, yet the appropriate therapy remains unknown. Radiation therapy at conventional doses results in destruction of normal tissue, which has suggested that full-dose chemotherapy might result in unacceptable toxicity in A-T patients with cancer. PROCEDURE The medical records of 412 A-T patients were reviewed to identify those patients who developed lymphoid malignancies and to analyze the type and duration of therapy, events during therapy, and off-therapy follow-up. RESULTS Of 74 A-T patients with lymphoid malignancies, 32 patients received chemotherapy. The 21 patients treated with standard chemotherapy had a significantly better median survival (9 months, range, 1-162+ months vs. 5 months, range, 0.5-28 months) (P = 0.03) and complete remission rate (76% vs. 9%) (P = 0.001) than the 11 treated with reduced dose chemotherapy. Three of the 21 full-dose chemotherapy patients required dose reductions because of neutropenia. Seven of the 14 patients exposed to 1,200 mg/m2 or greater of cyclophosphamide developed hemorrhagic cystitis. All three patients exposed to bleomycin developed pulmonary disease which was fatal in two. Of the 16 standard-dose chemotherapy patients who achieved a complete remission, two remain disease-free, five have died of recurrent disease, and five died of pulmonary disorders and four of other causes while in remission. CONCLUSIONS Standard-dose chemotherapy should be given to each A-T patient with a lymphoid malignancy unless additional physical or emotional problems make it unlikely that the patient will benefit. Morbidity and mortality may be reduced by prophylaxis against hemorrhagic cystitis and early detection and treatment of pulmonary disorders.

Radiosensitivity of normal tissues in ataxia-telangiectasia heterozygotes ☆

PURPOSE Approximately 5% of cancer patients given radiation therapy exhibit severe injuries to the noncancerous tissue in the radiation field. Striking clinical sensitivity to ionizing radiation has been observed frequently in ataxia-telangiectasia (A-T) homozygotes. This study was undertaken to test the hypothesis that heterozygous carriers of a mutated gene for A-T may represent a substantial proportion of all patients who suffer severe radiation toxicity. METHODS The medical records of all A-T heterozygotes treated with radiation therapy for breast or prostate cancer were compiled from an ongoing study of mortality and cancer incidence in A-T families. Diagnostic, treatment, and follow-up records were reviewed. Acute and long-term radiation complications were scored according to Radiation Therapy and Oncology Group criteria. RESULTS There were no instances of soft tissue necrosis or other apparent serious injuries to normal tissues of two A-T heterozygotes with prostate carcinoma and 11 with breast carcinoma who received moderate-to-high doses of conventionally fractionated radiation therapy by megavoltage techniques. CONCLUSION There is no evidence that abnormal clinical radiosensitivity occurs in A-T heterozygotes receiving conventionally fractionated radiation therapy for breast or prostate cancer.

Neutral sequence variants and haplotypes at the 150 Kb ataxia-telangiectasia locus

Sequence variants occur every few hundred bases in the human genome. We evaluated the relationship between disease-causing mutations and neutral sequence variants at the 150 Kb ataxia-telangiectasia (A-T) locus. Mutations at this locus cause a distinct autosomal recessive syndrome in homozygotes and predispose heterozygotes to cancer and coronary heart disease. Nine common neutral sequence variants were observed in the coding and splice junction regions of 132 chromosomes from Caucasian individuals of European origin. Each of these variants appeared frequently in both A-T and non-A-T chromosomes. However, there was remarkable linkage disequilibrium between the polymorphic loci, resulting in only 7 haplotypes in analyzed chromosomes. These 7 haplotypes fell into 3 major ancestral groups. No individual polymorphic variant or haplotype correlated reliably with the presence of an A-T mutation. Thus, comparing the frequency of neutral variants at the A-T locus in diseased and non-diseased populations is unlikely to uncover the relationship of mutations at this locus to common diseases. These data reflect general limitations on using single nucleotide polymorphisms (SNPs) to identify loci for many common diseases.