One test to identify 50% of all Norwegian BRCA1 mutations
KeywordsGenetic Counselling Health Authority BRCA1 Mutation Normal Product Product Size
In Norway, 1675delA, 1135insA and 816delGT together account for more than half of all BRCA1 mutations in breast-ovarian cancer kindreds (Disease Markers 1999, 15:79-84). We have set up a system for determining absence/presence of these three mutations. DNA is isolated from frozen, whole blood using the GenoPrep instrument for automated nucleic acid purification. The automated system is based on the use of magnetic microparticles, giving high quality DNA for PCR-reactions. The instrument can process 48 samples at a time. The system is designed to handle 100 μ l blood per sample and produces quantities of DNA sufficient for at least 100 PCR reactions (approximately 3 μ g). A multiplex PCR-based fragment analysis has been established employing 30 PCR cycles on a GeneAmp System 7600 cycler (PE-AB). The resulting three fragments are subjected to gel electrophoresis after denaturation by means of the Alf Express™(Pharmacia Biotech) for 160min, and all fragments scored for size variations due to insertions/deletions. The normal product sizes for the three amplified fragments are 85 bp (816delA), 140bp (1135insA) and 63 bp (1675delA), respectively. Probable mutants are verified by sequencing.
Norwegian health authorities have confirmed that the treating physician may obtain informed consent and obtain blood for mutation analysis; the patient is referred to genetic counselling when a mutation is demonstrated. The activity will define patients and families with mutations for health care, it is cost effective (Disease Markers 1999, 15:167-173), and we may obtain population-based estimates of prevalences, penetrances and expressions of the mutations.