Rapid and accurate determination of (CAG)(n) repeats in the androgen receptor gene using polymerase chain reaction and automated fragment analysis

Objectives: To develop and evaluate a new method for determination of the C AG repeat length in Exon 1 of the androgen receptor gene. Design and Methods: The method is based on PCR amplification of a DNA regio n encompassing the repeats and analysis of the length of the PCR product on a sequencing gel. One of the PCR primers was labeled with Cy5.5 fluorescen t dye to facilitate detection after laser excitation. We used a fully autom ated system for electrophoretic separation of the PCR product and accurate sizing of the length of the PCR product using fragment analysis. Results: The major advantages of the new technique are its simplicity, spee d, accuracy, and reproducibility. Analysis of the CAG repeats in genomic DN As from 18 males indicated that they were all hemizygous with a mean CAG re peat number of 22 (range 20-30 repeats). Among 60 DNAs from females, 16 wer e homozygous and 44 were heterozygous. The repeat length ranged from 17-30 with a mean of 22. In both males and females, the distribution of CAG repea ts was bimodal. Conclusion: We anticipate that this improved method for CAG repeat analysis will find applications in clinical studies involving prostate and breast c ancer patients. Copyright (C) 1999 The Canadian Society of Clinical Chemist s.