Analysis of 3297 individuals suggests that the pathogenic germline 5'-UTR variant BRCA1 c.-107A > T is not common in south-east Germany.

In this study we aim to determine the prevalence of the recently identified pathogenic BRCA1 variant c.-107A > T in the south-east German population. This variant causes the epigenetic silencing of the BRCA1 promotor and has been detected in two independent families from the UK without a germline BRCA1 or BRCA2 pathogenic variant. A total of 3297 individuals with suspicion of hereditary breast and ovarian cancer and fulfilling the clinical criteria necessary for genetic testing in Germany were analyzed for presence of the variant by a Kompetitive Allele-Specific PCR (KASP) assay or direct Sanger sequencing. Since we did not detect an individual carrying the variant we conclude that BRCA1 c.-107A > T is not a common variant in the south-east German population.

FMR1 gene deletion/reversion: a pitfall of fragile X carrier testing.

The Fragile X syndrome is, in the majority of cases, caused by CGG trinucleotide amplification within the FMR1 gene. The syndrome is rarely caused by point mutations or deletions. Here we describe a family with 2 sons and 1 daughter affected by Fragile X syndrome and 2 unaffected daughters whose carrier status was unknown prior to this study. Analysis of DNA from each of the 2 daughters revealed two alleles in the normal size range. However, 1 daughter carried one allele of 10 CGG repeats that was not present in either the mother or the father. No evidence for mosaicism could be detected. Haplotype analysis of flanking polymorphic markers revealed that the 10 CGG allele was derived from the mutated allele inherited from the mother. Thus, this case most likely represents an additional case of a reverse mutation from a premutation allele in a female to a normal-sized allele in the offspring. It remains unclear how frequently such reversion events occur. The observation has important consequences for genetic testing, because many laboratories prescreen for the Fragile X syndrome by determining the length of the CGG repeat using PCR. If this shows alleles in the normal size range, a diagnosis of Fragile X syndrome is considered to be excluded. Because the routine PCR and/or Southern blot analyses alone may yield false-negative results in cases of a regression of the number of CGG repeats, we strongly recommend the inclusion of fragment length or haplotype analysis when determining the carrier status within Fragile X syndrome families.