Large rearrangements have recently been identified in the BRCA1 gene. Inclu
sion of a method for identifying such rearrangements should now be a prereq
uisite for providing a comprehensive mutation detection strategy. We have d
eveloped a semiquantitative PCR-based fluorescent assay for the detection o
f previously identified deletions. This method avoids the need for long PCR
or Southern blotting and is suitable for large-scale epidemiological studi
es. The assay was used to screen 44 high-risk families within the U.K. York
shire Health Region. No deletions were detected, but five cases (11%) with
an apparent duplication of exon 13 in BRCA1 were identified. The presence o
f this mutation was confirmed by long PCR. Further developments include ext
ending the assay to include all exons of BRCA1.