1. ¹Translational Cancer Genetics Team, The Institute of Cancer Research, 15 Cotswold Rd, Sutton Surrey SM2 5NG, UK
2. ²Sharett Institute of Oncology, Hadassah University Medical Center, Jerusalem 92000, Israel
3. ³Royal Marsden NHS Foundation Trust, Fulham Rd, London SW3 6JJ, UK
4. ⁴Molecular Cytogenetics, The Institute of Cancer Research, 15 Cotswold Rd, Sutton Surrey SM2 5NG, UK

Correspondence: Zsofia Kote-Jarai, E-mail: zsofia.kote-jarai@icr.ac.uk

⁵Joint first authors.

Revised 27 October 2005; Accepted 18 November 2005; Published online 13 December 2005.

Abstract

Deleterious mutations in the BRCA1 gene predispose women to an increased risk of breast and ovarian cancer. Many functional studies have suggested that BRCA1 has a role in DNA damage repair and failure in the DNA damage response pathway often leads to the accumulation of chromosomal aberrations. Here, we have compared normal lymphocytes with those heterozygous for a BRCA1 mutation. Short-term cultures were irradiated (8Gy) using a high dose rate and subsequently metaphases were analysed by 24-colour chromosome painting (M-FISH). We scored the chromosomal rearrangements in the metaphases from five BRCA1 mutation carriers and from five noncarrier control samples 6 days after irradiation. A significantly higher level of chromosomal damage was detected in the lymphocytes heterozygous for BRCA1 mutations compared with normal controls; the average number of aberrations per mitosis was 3.48 compared with 1.62 in controls (P=0.0001). This provides new evidence that heterozygous mutation carriers have a different response to DNA damage compared with noncarriers and that BRCA1 has a role in DNA damage surveillance. Our finding has implications for treatment and screening of BRCA1 mutation carriers using modalities that involve irradiation.