Background: RAD51C is important in DNA repair and individuals with pathogenic RAD51C variants have increased risk of hereditary breast and ovarian cancer syndrome (HBOC), an autosomal dominant genetic predisposition to early onset breast and/or ovarian cancer.Methods: Five female HBOC probands sequenced negative for moderate‐ and high‐risk genes but shared a recurrent variant of uncertain significance in RAD51C (NM_058216.3: c.571 + 4A > G). Participant recruitment was followed by haplotype and case/control analyses, RNA splicing analysis, gene and protein expression assays, and Sanger sequencing of tumors.Results: The RAD51C c.571 + 4A > G variant segregates with HBOC, with heterozygotes sharing a 5.07 Mbp haplotype. RAD51C c.571 + 4A > G is increased ~52‐fold in the Newfoundland population compared with the general Caucasian population and positive population controls share disease‐associated alleles, providing evidence of a founder effect. Splicing analysis confirmed in silico predictions that RAD51C c.571 + 4A > G causes exon 3 skipping, creating an immediate premature termination codon. Gene and protein expression were significantly reduced in a RAD51C c.571 + 4G > A heterozygote compared with a wild‐type relative. Sanger sequencing of tumors from two probands indicates loss‐of‐heterozygosity, suggesting loss of function.Conclusion: The RAD51C c.571 + 4A > G variant affects mRNA splicing and should be re‐classified as pathogenic according to American College of Medical Genetics and Genomics guidelines.

The island of Newfoundland, the first of England’s overseas colonies, was settled from the 17th century onward by restricted numbers of English, Irish, and French immigrants, in small “outport” communities that have maintained geographic, religious, and linguistic isolation to the latest generations. To measure the extent of modification and loss of genetic variation through founder effect, drift, and inbreeding in this historically isolated population, we analyzed the complete mitochondrial DNA (mtDNA) genomes and 14 microsatellite loci from each of 27 individuals with matrilineal ancestries extending to the colonial period. Every individual has a unique mtDNA genome sequence. All but one of these genomes are assignable to one of five major (H,J,K,T, and U) or minor (I) European haplogroups. The possibility of homoplasy at single nucleotide polymorphism (SNP) sites that define subtypes within the H haplogroup is discussed. Observed haplogroup proportions do not differ significantly from those of western Europeans or between English and Irish Newfoundlanders. The exceptional individual is a member of haplogroup A2, who appears to be the descendant of a Mi’kmaq First Nations mother and a French father, a common marriage pattern in the early settlement of Newfoundland. Microsatellite diversity is high (H_E= 0.763), unstructured with respect to mtDNA haplotype or ethnicity, and there is no evidence of linkage disequilibrium. There is a small but significant degree of inbreeding (F_IS= 0.0174). Collection of whole mtDNA genome data was facilitated by the use of microarray sequencing, and we describe a simple algorithm that is 99.67% efficient for sequence recovery.

Pathogenic variants (PVs) in BRCA1 and BRCA2 increase the lifetime risks of breast and ovarian cancer. Guidelines recommend breast screening (magnetic resonance imaging (MRI) and mammogram) or risk-reducing mastectomy (RRM) and salpingo-oophorectomy (RRSO). We sought to (1) characterize the population of BRCA1/2 PV carriers in Newfoundland and Labrador (NL), (2) evaluate risk-reducing interventions, and (3) identify factors influencing screening and prevention adherence. We conducted a retrospective study from a population-based provincial cohort of BRCA1/2 PV carriers. The eligibility criteria for risk-reducing interventions were defined for each case and patients were categorized based on their level of adherence with recommendations. Chi-squared and regression analyses were used to determine which factors influenced uptake and level of adherence. A total of 276 BRCA1/2 PV carriers were identified; 156 living NL biological females composed the study population. Unaffected females were younger at testing than those with a cancer diagnosis (44.4 years versus 51.7 years; p = 0.002). Categorized by eligibility, 61.0%, 61.6%, 39.0%, and 75.7% of patients underwent MRI, mammogram, RRM, and RRSO, respectively. Individuals with breast cancer were more likely to have RRM (64.7% versus 35.3%; p < 0.001), and those who attended a specialty hereditary cancer clinic were more likely to be adherent to recommendations (73.2% versus 13.4%; p < 0.001) and to undergo RRSO (84.1% versus 15.9%; p < 0.001). Nearly 40% of the female BRCA1/2 PV carriers were not receiving breast surveillance according to evidence-based recommendations. Cancer risk reduction and uptake of breast imaging and prophylactic surgeries are significantly higher in patients who receive dedicated specialty care. Organized hereditary cancer prevention programs will be a valuable component of Canadian healthcare systems and have the potential to reduce the burden of disease countrywide.

The spontaneous development of juvenile-onset, ovarian granulosa cell (GC) tumors in the SWR/Bm (SWR) inbred mouse strain is a model for juvenile-type GC tumors that appear in infants and young girls. GC tumor susceptibility is supported by multiple Granulosa cell tumor (Gct) loci, but the Gct1 locus on Chr 4 derived from SWR strain background is fundamental for GC tumor development and uniquely responsive to the androgenic precursor dehydroepiandrosterone (DHEA). To resolve the location of Gct1 independently from other susceptibility loci, Gct1 was isolated in a congenic strain that replaces the distal segment of Chr 4 in SWR mice with a 47 × 106-bp genomic segment from the Castaneus/Ei (CAST) strain. SWR females homozygous for the CAST donor segment were confirmed to be resistant to DHEA- and testosterone-induced GC tumorigenesis, indicating successful exchange of CAST alleles (Gct1 CA) for SWR alleles (Gct1 SW) at this tumor susceptibility locus. A series of nested, overlapping, congenic sublines was created to fine-map Gct1 based on GC tumor susceptibility under the influence of pubertal DHEA treatment. Twelve informative lines have resolved the Gct1 locus to a 1.31 × 106-bp interval on mouse Chr 4, a region orthologous to human Chr 1p36.22.

Females of the SWR/Bm (SWR) inbred mouse strain possess a unique susceptibility to juvenile-onset tumors originating from the granulosa cells (GC) of the ovarian follicles. Tumor susceptibility is an inherited, polygenic trait in SWR females, minimally involving an oncogenic Granulosa cell tumor susceptibility (Gct) locus on chromosome (Chr) 4 (Gct1), and two GC tumor susceptibility modifier genes mapped to distinct regions of Chr X (Gct4 and Gct6). Shifts in the frequency of GC tumor initiation in the SWR female population from low penetrance to moderate penetrance, or phenotype switching between GC tumor-susceptible and GC tumor-resistant, is strongly influenced by the allelic contributions at Gct4 and Gct6. In addition to the allele-specific effects, GC tumor susceptibility is controlled by the mode of X-linked transmission with a dominant, paternal parent-of-origin effect. We took advantage of the robust paternal effect with a recombinant male progeny testing strategy to resolve the Gct4 locus interva...

BRCA1 and 2 pathogenic variants increase lifetime risks of breast (50-75%) and ovarian cancer (15-20%). Guidelines recommend breast screening (MRI and mammogram) or risk-reducing mastectomy with salpingo-oophorectomy for ovarian cancer prevention. We sought to 1) characterize the population of BRCA1/2 carriers in Newfoundland and Labrador (NL) 2) evaluate risk-reducing interventions 3) identify factors influencing screening and prevention adherence. Methods: This is a retrospective study from a population-based provincial cohort of BRCA1/2 carriers. Eligibility criteria for risk-reducing interventions were defined for each case and patients were categorized based on their level of adherence with recommended screening or prevention. Chi-squared and regression analyses were used to determine which factors influenced uptake and level of adherence. Results: 276 BRCA1/2 carriers were identified; 156 living NL females composed the study population. Unaffected females were younger at testing than those with a cancer diagnosis (44.4 y versus 51.7 y; p=0.002). Categorized by eligibility, 61.0%, 61.6%, 39.0% and 75.7% of patients underwent MRI, mammogram, risk-reducing mastectomy, and risk-reducing salpingo-oophorectomy, respectively. Individuals with breast cancer were more likely to have risk-reducing mastectomy (64.7% versus 35.3%; p<0.001), and those who attended specialty hereditary cancer clinic were more likely to be adherent with breast/ovarian cancer recommendations (73.2% versus 13.4%; p<0.001) and to undergo risk-reducing salpingo-oophorectomy(84.1% versus 15.9%; p<0.001). Conclusions: Nearly 40% of female BRCA1/2 carriers were not receiving breast surveillance according to evidence-based recommendations. Cancer risk reduction and uptake of breast imaging and prophylactic breast and pelvic surgeries are significantly higher in patients who receive dedicated specialty care. Organized hereditary cancer prevention programs will be a valuable component of Canadian health care systems and have the potential to reduce the burden of disease country-wide.