Common Founder Mutation Research Articles

Olaparib sensitivity observed in metastatic pancreatic cancer (mPaC) with a wide spectrum of germline BRCA1 and BRCA2 mutations (gBRCAm).

4621 Background: The POLO study (NCT02184195) showed that mPaC patients (pts) with a deleterious or suspected deleterious gBRCAm, and whose disease had not progressed during ≥16 weeks of first-line platinum-based chemotherapy, had significantly longer progression-free survival (PFS, primary endpoint) with maintenance olaparib vs placebo: median 7.4 vs 3.8 months, hazard ratio (HR) 0.53; P=0.004. PFS benefit was observed in pts with g BRCA1m (HR 0.40) and g BRCA2m (HR 0.63). The POLO study represents the largest BRCAm prevalence study in pancreatic cancer. We report additional exploratory analysis to further characterize patient gBRCAm profiles, including the relationship with efficacy. Methods: Pts were enrolled based on either a previously identified gBRCAm status from a local test result and subsequently confirmed by central testing, or a prospectively identified gBRCAm. Pts received maintenance olaparib 300 mg twice daily (tablet) or placebo. PFS was assessed by blinded independent central review (modified RECIST v1.1). Results: Of 3194 prospectively screened pts, a valid BRCA test result was obtained for 3175 (99%) from 12 countries; gBRCAm prevalence was 6.2% in pts not previously known to harbor a gBRCAm (196/3175; 1.6% g BRCA1m, 4.5% g BRCA2m). In countries (n=8) with >100 pts prospectively tested, highest gBRCAm prevalence was 9.2% (USA) and lowest 4.0% (Spain). Prevalence by race (>100 pts); 6.4% Caucasian, 4.6% Asian. In total, 154 pts with a gBRCAm satisfied all eligibility criteria and were randomized (106 prospectively tested and 48 by local test [44/48 subsequently confirmed by Myriad testing]). 37/154 (24%) randomized pts carried a common Ashkenazi Jewish founder mutation, the majority being from Israel (21 pts). From a total of 151 variants, frameshift mutations were most frequent (g BRCA1m 69.6%, g BRCA2m 71.4%) followed by nonsense mutations (g BRCA1m 6.5%, g BRCA2m 17.1%). The efficacy (PFS) of olaparib vs placebo in the different subgroups are shown in the table. Conclusions: In pts with mPaC enrolled in POLO, g BRCA2m were more prevalent than g BRCA1m and mutation type was predominantly frameshift. PFS benefit was consistent across a heterogenous spectrum of gBRCAm and with the previously reported full analysis set. Clinical trial information: NCT02184195 . [Table: see text]

Biallelic germline BRCA1 mutations in a patient with early onset breast cancer, mild Fanconi anemia-like phenotype, and no chromosome fragility.

BackgroundBiallelic BRCA1 mutations are regarded either embryonically lethal or to cause Fanconi anemia (FA), a genomic instability syndrome characterized by bone marrow failure, developmental abnormalities, and cancer predisposition. We report biallelic BRCA1 mutations c.181T > G (p.Cys61Gly) and c.5096G > A (p.Arg1699Gln) in a woman with breast cancer diagnosed at the age of 30 years. The common European founder mutation p.Cys61Gly confers high cancer risk, whereas the deleterious p.Arg1699Gln is hypomorphic and was suggested to confer intermediate cancer risk.Methods and ResultsAside from significant toxicity from chemotherapy, the patient showed mild FA‐like features (e.g., short stature, microcephaly, skin hyperpigmentation). Chromosome fragility, a hallmark of FA patient cells, was not present in patient‐derived peripheral blood lymphocytes. We demonstrated that the p.Arg1699Gln mutation impairs DNA double‐strand break repair, elevates RAD51 foci levels at baseline, and compromises BRCA1 protein function in protecting from replication stress. Although the p.Arg1699Gln mutation compromises BRCA1 function, the residual activity of the p.Arg1699Gln allele likely prevents from chromosome fragility and a more severe FA phenotype.ConclusionOur data expand the clinical spectrum associated with biallelic BRCA1 mutations, ranging from embryonic lethality to a mild FA‐like phenotype and no chromosome fragility.

Variable Features of Juvenile Polyposis Syndrome With Gastric Involvement Among Patients With a Large Genomic Deletion of BMPR1A.

OBJECTIVES:Loss-of-function mutations of BMPR1A cause juvenile polyposis syndrome (JPS), but large genomic deletions in BMPR1A are rare, reported in few families only, and data regarding the associated phenotype are limited.METHODS:We investigated clinical features and genomic data of 7 extended seemingly unrelated families with a genomic deletion of the entire coding region of BMPR1A. We defined mutation size, mutation prevalence, and tumor pathogenesis using whole-genome sequencing, targeted genotyping, and haplotype analysis.RESULTS:Patients with JPS from 7 families of Bukharin Jewish ancestry carried a deletion of 429 kb, encompassing the BMPR1A coding sequence and 8 downstream genes. Haplotype analysis and testing controls identified this as a common founder mutation occurring in 1/124 individuals of Bukharin origin. Tumor testing did not demonstrate loss of heterozygosity. Among carriers, JPS was almost fully penetrant, but clinical features varied widely, ranging from mild to very severe, including pan-enteric polyps, gastritis, and colorectal, esophageal, and testicular cancer, and carriers with phenotypes, which would not have raised suspicion of JPS.DISCUSSION:The phenotype in this large cohort was extremely variable, although all carriers shared the same variant and the same genetic background. New observations include a preponderance of adenomatous rather than juvenile polyps, possible association with testicular cancer, and unexpected upper gastrointestinal involvement.

Clinical and molecular findings in a cohort of ANO5-related myopathy.

Objective ANO5‐related myopathy is an important cause of limb‐girdle muscular dystrophy (LGMD) and hyperCKemia. The main descriptions have emerged from European cohorts, and the burden of the disease worldwide is unclear. We provide a detailed characterization of a large Brazilian cohort of ANO5 patients.MethodsA national cross‐sectional study was conducted to describe clinical, histopathological, radiological, and molecular features of patients carrying recessive variants in ANO5. Correlation of clinical and genetic characteristics with different phenotypes was studied.ResultsThirty‐seven patients from 34 nonrelated families with recessive mutations of ANO5 were identified. The most common phenotype was LGMD, observed in 25 (67.5%) patients, followed by pseudometabolic presentation in 7 (18.9%) patients, isolated asymptomatic hyperCKemia in 4 (10.8%) patients, and distal myopathy in a single patient. Nine patients presented axial involvement, including one patient with isolated axial weakness. The most affected muscles according to MRI were the semimembranosus and gastrocnemius, but paraspinal and abdominal muscles, when studied, were involved in most patients. Fourteen variants in ANO5 were identified, and the c.191dupA was present in 19 (56%) families. Sex, years of disease, and the presence of loss‐of‐function variants were not associated with specific phenotypes.InterpretationWe present the largest series of anoctaminopathy outside Europe. The most common European founder mutation c.191dupA was very frequent in our population. Gender, disease duration, and genotype did not determine the phenotype.

Spinocerebellar ataxia with axonal neuropathy type 1 revisited

Spinocerebellar ataxia with axonal neuropathy type 1 (SCAN1; OMIM #607250), an exceedingly rare disorder having been documented in only a single family from Saudi Arabia, is the result of an unusual mutation in the tyrosyl DNA phosphodiesterase 1 gene (TDP1). We performed high-throughput sequencing (whole exome and ataxia gene panel) in two apparently unrelated Omani families segregating sensorimotor neuropathy and ataxia in an autosomal recessive fashion. Following validation by Sanger sequencing, all affected subjects (n = 4) were confirmed to carry the known SCAN1 pathogenic homozygous variant in the TDP1 gene, NM_001008744.1:c.1478A > G (p.His493Arg). In keeping with the initial description, our patients demonstrated progressive ataxia, cerebellar atrophy and disabling axonal sensori-motor neuropathy (n = 4), hypercholesterolemia (n = 2) and elevated serum alpha fetoprotein (n = 3). In addition, our patients also had mild cognitive deficits in multiple domains (n = 3), a feature not previously reported. Our findings independently revalidate the phenotype of TDP1 mutation and expand the clinical spectrum to include mild cognitive deficits. Haplotype sharing, as determined by DNA microarray (CytoScan HD), attests to a possible common founder mutation in the Arab population.

Similar 10-Year Survival in Breast Cancer Patients of Lithuania and Poland with Common BRCA1 Founder Mutations

Similar 10-Year Survival in Breast Cancer Patients of Lithuania and Poland with Common BRCA1 Founder Mutations

No Hot Spot Mutations CHRNE c.1327 delG, CHAT c.914T>C, and RAPSN c.264C>A in Iranian Patients with Congenital Myasthenic Syndrome.

We aimed to perform genetic testing and clinical data of patients with Congenital Myasthenic Syndrome, a rare disorder caused by mutations in genes encoding molecules expressed in the neuromuscular junction and constitutes fatigable muscle weakness. Sixteen patients were screened in Taban Clinic, Tehran, Iran from 2014 to 2015 for the hot spot mutations in known CMSs genes (CHRNE, CHAT, RAPSN) based on clinical data. PCR was performed and then direct DNA sequencing was done for mutation identification. Most patients represented the criteria of Congenital Myasthenic Syndrome in view of early ptosis, motor delay, normal mental development, easy fatigability, decrement in repetitive nerve stimulation test of EMG-NCV and a negative result for antibody against of acetylcholine receptor. No variations were found in the mutational analysis of the CHRNE gene. Analysis of CHAT gene revealed c.358G>A (P. A120T) variation in 9 patients. In the gene RAPSN, polymorphism c.456T>C )P.Y152Y) and polymorphism c.193-15C>T (IVS1-15C>T) were identified in 11 and one patients, respectively. The common founder mutations of involved genes in CMSs could be very rare among ethnic Iranian. Screening of the entire genes would be efficient to distinguish the specific mutations in specific ethnicity.

Monoallelic MUTYH carrier status is not associated with increased breast cancer risk in a multigene panel cohort

Whether monoallelic MUTYH mutations increase female breast cancer risk remains controversial. This study aimed to determine if monoallelic MUTYH mutations are associated with increased breast cancer risk in women undergoing multigene panel testing (MGPT). The prevalence of monoallelic MUTYH mutations was compared between Non-Hispanic white female breast cancer cases (n = 30,456) and cancer-free controls (n = 12,289), all of whom underwent MGPT that included MUTYH. We tested breast cancer associations with MUTYH alleles using Fisher's exact test, followed by multivariate logistic regression adjusted for age at testing and MGPT type ordered. Frequencies of the two most common MUTYH founder mutations, p.G396D and p.Y179C, were compared independently between the breast cancer cases and MGPT controls, as well as the healthy UK10K control population (n = 2640). Comparing cases to MGPT controls, no association was observed between female breast cancer and any monoallelic MUTYH carrier status (OR 0.86-1.36, p = 0.21-0.96). Similarly, comparisons to UK10K controls revealed no significant increase in breast cancer risk associated with p.G396D (OR 1.20, p = 0.44) or p.Y179C (OR 1.71, p = 0.24). This study did not find a significant increase in breast cancer risk associated with monoallelic MUTYH mutations.

Abstract 4351: Intratumoral heterogeneity and process of evolution of intrahepatic cholangiocarcinoma

Abstract Background: Intrahepatic cholangiocarcinoma(ICC) accounts for about 10% of all primary liver cancer. South Asia and a part of Chile, but in recent years it has been increasing in other areas including Europe and the United States. The only potentially curative treatment for patients who have a resectable tumor is surgery. Unfortunately, even after curative-intent surgery, the clinical outcomes of patients undergoing liver resection are disappointing, with a 5-year survival rate of 20% to 35%. Furthermore, the role of the other treatments, including systemic chemotherapy and radiotherapy, remain poorly defined and have been reported to have a favorable therapeutic effect. In this study, we reveals the intratumoral heterogeneity and process of evolution of intractable ICC without fully genomic understanding. Material and method: Surgical specimens of 10 patients with resection of ICC in curative intention were acquired between 10/2014 and 5/2016. The average tumor size was 47 mm(range 30-80 mm). We obtained 57 samples at 3-9 lesions for each case, and performed whole exome sequencing using the next generation sequencer (HiSeq2500). Multiregional analysis was performed respectively on these cases, and we investigated intratumoral heterogeneity of ICC. Furthermore, we guessed the process of clonal evolution of ICC from the result of whole exome sequencing. Result: We defined "Founder mutation" as only a mutation present in all samples in each case , and defined “Progressor mutation” as several mutations present in some samples in each case. Furthermore, we classified “Progressor mutation” as “Shared mutation” present in several samples in each case but not all and “Unique mutation” present in one sample in each case). In 10 cases, mean number of Founder, Unique and Shared mutation were 53%(range 24-74%), 18%(range 5-40%), and 29%(range 6-54%), respectively, and this indicated intratumoral heterogeneity in ICC. In addition, Founder mutation mainly including TP53, SMAD4, and NRAS were common in 2 cases, but no common Founder mutation was observed in over 3 cases, so this indicated intratumoral heterogeneity in ICC. This results leaded to the process of clonal evolution during tumor formation, describing the evolutionary trees. Conclusion: In this study, multiregional analysis was performed on samples of ICC, and intratumoral heterogeneity and the process of clonal evolution were evaluated. This result confirms the resistance to current treatment and it seems that it is necessary to search for further therapeutic targets. Citation Format: Akihiro Kitagaw, Hisateru Komatsu, Yosuke Kuroda, Syuhei Ito, Takaaki Masuda, Hidetoshi Eguchi, Hidetoshi Eguchi, Yuichiro Doki, Masaki Mori, Koshi Mimori. Intratumoral heterogeneity and process of evolution of intrahepatic cholangiocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4351.

Variants in FIX propeptide associated with vitamin K antagonist hypersensitivity: functional analysis and additional data confirming the common founder mutations.

One of the most common and unwanted side effects during oral anticoagulant therapy (OAT) is bleeding complications. In rare cases, vitamin K antagonist (VKA)-related bleeding events are associated with mutations affecting the F9 propeptide at amino acid position 37 due to a substitution of alanine to either valine or threonine. Based on our actual cohort of 18 patients, we update the knowledge on this rare phenotype and its origin. A founder mutation for both variants was reconfirmed by haplotype analysis of intronic and extragenic short tandem repeat (STR) polymorphisms with a higher prevalence in Switzerland than in other regions of Europe. Screening of healthy individuals for the presence of these F9 gene mutations did not identify any of these variants, thus proving the rare occurrence of this genotype. Furthermore, both variants were expressed in vitro and warfarin dose responses were studied. Our warfarin dose response analysis confirmed higher sensitivity of both variants to warfarin with the effect being more apparent for Ala37Thr. Thus, although F9 propeptide mutation-associated hypersensitivity to VKA is a rare phenomenon, awareness towards this bleeding phenotype is important to identify patients at risk.

Founder Effect of the RETC611Y Mutation in Multiple Endocrine Neoplasia 2A in Denmark: A Nationwide Study.

Multiple endocrine neoplasia (MEN) 2A and 2B are caused by REarranged during Transfection (RET) germline mutations. In a recent nationwide study, an unusually high prevalence (33%) of families with the C611Y mutation was reported, and it was hypothesized that this might be due to a founder effect. The first nationwide study of haplotypes in MEN2A families was conducted, with the aim of investigating the relatedness and occurrence of de novo mutations among Danish families carrying similar mutations. The study included 21 apparently unrelated MEN2A families identified from a nationwide Danish RET cohort from 1994 to 2014. Twelve, two, two, three, and two families carried the C611Y, C618F, C618Y, C620R, and C634R mutations, respectively. Single nucleotide polymorphism chip data and identity by descent analysis were used to assess relatedness. A common founder mutation was found among all 12 C611Y families and between both C618Y families. No relatedness was identified in the remaining families. The data suggest that all families with the C611Y germline mutation in Denmark originate from a recent common ancestor, probably explaining the unusually high prevalence of this mutation. Additionally, the results indicate that the C611Y mutation rarely arises de novo, thus underlining the need for thorough multigenerational genetic work up in carriers of this mutation.

OP22.08: Integrating ultrasound findings with chromosomal microarray stretches of homozygosity and principles in founder populations

Chromosomal microarray (CMA) analysis is effectively applied prenatally to detect copy number changes. SNP probes included on the microarray platform can detect regions of excessive homozygosity (ROH) and identical-by-descent genomic stretches. The utility of the latter in prenatal diagnosis is not well established. Recessive founder mutations have been identified within distinct ethnic groups. Combining these data with prenatal sonography provides accurate molecular diagnoses quickly. Three gravidae presenting with specific fetal sonographic findings: 1) ventriculomegaly with encephalocele; 2) severe polyhydramnion, and 3) enlarged echogenic kidneys, underwent amniocentesis for CMA, and Genome-Wide Human SNP array was used to analyse DNA from amniocytes. The Genomic Oligoarray and SNP array evaluation tool v3.0 was used to detect recessive loci associated with the reported clinical findings. Candidate regions were further interrogated using the National Genetic Database. Three fetuses from three distinct nuclear families in which the parents shared a similar ethnicity (either Ashkenazi or Bukharan Jews) but no reported consanguinity, were assessed. No copy number changes were observed, however evaluation of regions of homozygosity revealed a relevant candidate gene for the specific phenotype for each fetus. Using the National Genetic Database a specific mutation was examined in both parents (c.1167dupA mutation in the FKTN gene, c.167ins6[TTTCCC] mutation in the BSND gene and c.3761_3762delCCinsG in the PKHD1 gene, respectively). Both parents were found to be carriers and the fetuses homozygotes to the mutation. For the first time, specific sonographic pathology, data from ROH extracted from CMA results, and information regarding common founder mutations in distinct ethnic subgroups were combined to create a comprehensive streamlined approach to provide effective genetic diagnosis and counselling within the time constraints of ongoing pregnancy.

Abstract 1281: Germline mutations in NBN conferring DNA damage response defects are found in patients with multiple cancer types

Abstract Nibrin, the protein encoded by the NBN gene forms a complex with Mre11 and Rad51 (MRN complex) that is crucial for DNA damage repair. Mutations in NBN are found in >90% of patients with Nimjegen breakage syndrome (NBS), an autosomal recessive disorder characterized by growth retardation, microcephaly, radiosensitivity, immunodeficiency and increased cancer risk. Most of NBS patients harbor the common founder mutation c.657del5 that leads to expression of a hypomorphic 70kDa C-terminal fragment produced by alternative translation initiation. Cell lines derived from these patients show increased sensitivity to DNA-damaging agents, chromosome instability, and abnormal cell cycle checkpoint function. Several studies have addressed cancer incidence in individuals with germline NBN mutations, showing increased cancer risk for individuals harboring the c.657del5 founder mutation and for carriers of the R215W missense mutation across multiple cancer types. For other NBN mutations conflicting reports exist as to their association with cancer risk. Here, we report newly identified NBN germline frameshift and truncating mutations in patients with multiple cancer types, including prostate, lung, breast cancer, acute lymphocytic leukemia, and chronic lymphocytic leukemia. Modeling these mutations in an NBN-deficient cellular background showed expression of a novel C-terminal truncated fragment that can bind to Mre11. Cells expressing these mutant proteins display attenuated DNA damage repair function and decreased overall survival following induction of DNA damage. Impaired Chk2 phosphorylation was also observed, indicating cell cycle checkpoint deficiencies. Thus, the NBN germline mutations identified here could contribute to genomic instability predisposing to tumorigenesis. Further in vitro studies with these and additional germline mutations occurring in cancer patients are ongoing, in order to better understand the role of this pathway of DNA damage repair in susceptibility to malignancies. Citation Format: Sabine Topka, Michael F. Walsh, Ann Maria, Annie Lincoln, Diana Mandelker, Liying Zhang, Marc Ladanyi, Michael F. Berger, Mark E. Robson, Joseph Vijai, Kenneth Offit. Germline mutations in NBN conferring DNA damage response defects are found in patients with multiple cancer types [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1281. doi:10.1158/1538-7445.AM2017-1281

Next-generation sequencing targeted disease panel in rod-cone retinal dystrophies in Māori and Polynesian reveals novel changes and a common founder mutation.

This study identifies unique genetic variation observed in a cohort of Māori and Polynesian patients with rod-cone retinal dystrophies using a targeted next-generation sequencing retinal disease gene panel. With over 250 retinal disease genes identified, genetic diagnosis is still only possible in 60-70% of individuals and even less within unique ethnic groups. Prospective genetic testing in patients with rod-cone retinal dystrophies identified from the New Zealand Inherited Retinal Disease Database, PARTICIPANTS: Sixteen patients of Māori and Polynesian ancestry. Next-generation sequencing of a targeted retinal gene panel. Sanger sequencing for a novel PDE6B mutation in subsequent Māori patients. Genetic diagnosis, genotype-phenotype correlation. Thirteen unique pathogenic variants were identified in 9 of 16 (56.25%) patients in 10 different genes. A definitive genetic diagnosis was made in 7/16 patients (43.7%). Six changes were novel and not in public databases of human variation. In four patients, a homozygous, novel pathogenic variant (c.2197G > C, p.(Ala 733Pro)) in PDE6B was identified and also present in a further five similarly affected Māori patients. Over half of the Māori and Polynesian patients with inherited rod-cone diseases have no pathogenic variant(s) detected with a targeted retinal next-generation sequencing strategy, which is supportive of novel genetic mechanisms in this population. A novel PDE6B founder variant is likely to account for 16% of recessive inherited retinal dystrophy in Māori. Careful characterization of the clinical presentation permits identification of further Māori patients with a similar phenotype and simplifies the diagnostic algorithm.

Implementation of next-generation sequencing for molecular diagnosis of hereditary breast and ovarian cancer highlights its genetic heterogeneity.

Molecular diagnosis of hereditary breast and ovarian cancer (HBOC) by standard methodologies has been limited to the BRCA1 and BRCA2 genes. With the recent development of new sequencing methodologies, the speed and efficiency of DNA testing have dramatically improved. The aim of this work was to validate the use of next-generation sequencing (NGS) for the detection of BRCA1/BRCA2 point mutations in a diagnostic setting and to study the role of other genes associated with HBOC in Portuguese families. A cohort of 94 high-risk families was included in the study, and they were initially screened for the two common founder mutations with variant-specific methods. Fourteen index patients were shown to carry the Portuguese founder mutation BRCA2 c.156_157insAlu, and the remaining 80 were analyzed in parallel by Sanger sequencing for the BRCA1/BRCA2 genes and by NGS for a panel of 17 genes that have been described as involved in predisposition to breast and/or ovarian cancer. A total of 506 variants in the BRCA1/BRCA2 genes were detected by both methodologies, with a 100% concordance between them. This strategy allowed the detection of a total of 39 deleterious mutations in the 94 index patients, namely 10 in BRCA1 (25.6%), 21 in BRCA2 (53.8%), four in PALB2 (10.3%), two in ATM (5.1%), one in CHEK2 (2.6%), and one in TP53 (2.6%), with 20.5% of the deleterious mutations being found in genes other than BRCA1/BRCA2. These results demonstrate the efficiency of NGS for the detection of BRCA1/BRCA2 point mutations and highlight the genetic heterogeneity of HBOC.

BRCA1185delAG tumors may acquire therapy resistance through expression of RING-less BRCA1.

Heterozygous germline mutations in breast cancer 1 (BRCA1) strongly predispose women to breast cancer. BRCA1 plays an important role in DNA double-strand break (DSB) repair via homologous recombination (HR), which is important for tumor suppression. Although BRCA1-deficient cells are highly sensitive to treatment with DSB-inducing agents through their HR deficiency (HRD), BRCA1-associated tumors display heterogeneous responses to platinum drugs and poly(ADP-ribose) polymerase (PARP) inhibitors in clinical trials. It is unclear whether all pathogenic BRCA1 mutations have similar effects on the response to therapy. Here, we have investigated mammary tumorigenesis and therapy sensitivity in mice carrying the Brca1185stop and Brca15382stop alleles, which respectively mimic the 2 most common BRCA1 founder mutations, BRCA1185delAG and BRCA15382insC. Both the Brca1185stop and Brca15382stop mutations predisposed animals to mammary tumors, but Brca1185stop tumors responded markedly worse to HRD-targeted therapy than did Brca15382stop tumors. Mice expressing Brca1185stop mutations also developed therapy resistance more rapidly than did mice expressing Brca15382stop. We determined that both murine Brca1185stop tumors and human BRCA1185delAG breast cancer cells expressed a really interesting new gene domain-less (RING-less) BRCA1 protein that mediated resistance to HRD-targeted therapies. Together, these results suggest that expression of RING-less BRCA1 may serve as a marker to predict poor response to DSB-inducing therapy in human cancer patients.

Abstract P2-09-12: Prevalence of Hispanic BRCA1 and BRCA2 mutations among HBOC patients from Southern Brazil reveal differences among Latin American populations

Abstract Background.Breast cancer (BC) is the most common malignancy in women around the world, and 5% of BC cases and 15% of ovarian cancer (OC) cases can be attributed to BRCA1 and BRCA2 germline mutations, configuring Hereditary Breast and Ovarian Cancer Syndorme (HBOC). Considering that the genetic similarities between Latin American populations are largely unknown, we aimed to address if a panel of Hispanic BRCA mutations could be useful for a Brazilian population. Methods.Unrelated patients fulfilling NCCN criteria for HBOC syndrome were recruited. ASCO, Myriad and Penn II clinical testing criteria were analyzed for all patients. Blood-derived DNA samples were screened for 114 BRCA mutations, in a panel estimated to account for up to 90% of all BRCA Hispanic mutations (HISPANEL), using the Sequenom MassArray platform. Results. Among a total of 233 unrelated patients included (225 women and 8 men), 85% were BC patients and 14 patients were cancer unaffected. The mean age at diagnosis was 43 years for BC affected individuals and 45 years for patients with OC. Fifty-three patients fulfilled ASCO criteria, and 182 had Penn II≥10%, while only 64 had a Myriad score ≥10%. BRCA mutations were detected in 9 of 233 patients (prevalence of 3.86%). Among BC and/or OC affected individuals, this prevalence was 4.22%. Features of mutation carriers are depicted in table 1. Table 1. BRCA mutations identified in Brazilian HBOC patients Mutation Gender Tumor type and age at diagnosis Family history of cancer BRCA1 c.3331_3334delCAAGFemaleOvCa, 47; BrCa, 50Daughter BrCa≤20;Brother PrCa 54;Cousin BrCa≥ 50 BRCA1 c.5266dupCFemaleBilateral BrCa, 35 and 45Mother OvCa 58;Aunt OvCa 49;Cousin BrCa 49;Great-grandmother BrCa 90 BRCA1 c.5266dupCFemaleBrCa, 36Aunt BrCa 62;Cousin BrCa 45;Cousin BrCa 44;Cousin Bilateral BrCa 45;Cousin BrCa 44;Cousin OvCa 52 BRCA1 c.5266dupCFemaleOvCa, 52Mother OvCa 77;Sister BrCa 44;Aunt OvCa 66 BRCA1 c.5266dupCFemaleBilateral BrCa, 23 and 44Mother BrCa 45;Aunt Bilateral BrCa 48;Cousin BrCa 30;Aunt Bilateral BrCa 58;Grandmother BrCa BRCA1 c.5266dupCFemaleBilateral BrCa, 26Sister BrCa 50;Niece BrCa 28;Niece BrCa 30 BRCA1 c.5266dupCMaleBrCa, 64Daughter BrCa 34;Sister BrCa≤ 50;Sister BrCa 32 BRCA2 c.2806_2809delAAACFemaleBrCa, 49Sister BrCa 32;Sister BrCa 44;Aunt Bilateral BrCa 40 and 55 BRCA2 c.2806_2809delAAACFemaleBilateral triple negative BrCa, 42 and 55NoneBrCa=breast cancer; OvCa=ovarian cancer. Conclusions. The HISPANEL detects 59 BRCA1 and 55 BRCA2 mutations, including some mutations previously reported in Brazilian individuals. Most mutation carriers had the BRCA1 c.5266dupC (5382insC) mutation, a common founder mutation in several populations. Our results are largely different from other Latin American published data. Although low BRCA prevalence mutational rates were also seen in Peru and Mendellín (Colombia), in Mexico and Bogota (Colombia) a prevalence of 27% and 15%, respectively, was found in studies using HISPANEL and all studies included patients unselected for family history. Our findings reinforce that different Latin-American populations have different BRCA mutational profiles. Citation Format: Alemar B, Herzog J, Ashton-Prolla P, Weitzel J. Prevalence of Hispanic BRCA1 and BRCA2 mutations among HBOC patients from Southern Brazil reveal differences among Latin American populations. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-09-12.

Understanding complexity of Fanconi anaemia.

Understanding complexity of Fanconi anaemia.

MG-107 Congenital sucrase-isomaltase deficiency: Identification of the common inuit founder mutation

Objective Congenital sucrase-isomaltase deficiency (CSID) is a rare hereditary cause of chronic diarrhoea in children. Persons with CSID lack the intestinal brush-border enzyme required for digestion of di- and oligosaccharides, including sucrose and isomaltose. Malabsorption results in abdominal pain, distention, copious diarrhoea, and failure to thrive. If recognised, dietary avoidance of the offending carbohydrates is highly effective. Although CSID is known to be highly prevalent (˜5–10%) in several Inuit populations, the genetic basis for this condition has not been described. Methods We sequenced the sucrase-isomaltase gene, SI, in a single Inuit CSID proband with severe fermentative diarrhoea and failure to thrive. We then genotyped a further 128 anonymized Inuit control individuals from a variety of circumpolar locales to assess for a possible founder effect. Results We identified a novel, homozygous frameshift mutation, c.273_274delAG (p. Gly92Leufs*8) in exon 4 of SI in the proband, that is predicted to result in complete absence of functional protein product. This change is indeed very common among Inuit control specimens, with an observed allele frequency of 0.17 (95% confidence interval 0.13–0.22). The predicted Hardy-Weinberg prevalence of CSID in the Inuit, based on this single founder allele is ˜3% (95% confidence interval 1.6–5.0%), comparable with previous estimates. Interpretation Targeted mutation testing for the c.273_274delAG allele should afford a simple and minimally invasive means of diagnosing CSID in persons of Inuit descent. Because CSID is a readily treatable disorder, such testing should be considered at an early stage in the assessment of Inuit patients with chronic diarrhoea.

Abstract 5467: BRCA1 N-terminal-deficient proteins provide PARP inhibitor and platinum resistance

Abstract Introduction: Tumors harboring BRCA1 mutations initially respond well to platinum and PARP inhibitor therapy; however, resistance invariably arises and is a major clinical problem. The BRCA1 185delAG allele is a common founder mutation located close to the protein translation start site, thought to produce a short peptide devoid of function. Experimental procedures: In this study, we utilized the SUM1315MO2 breast cancer cell line that harbors a BRCA1 185delAG mutation to study mechanisms of PARP inhibitor and platinum resistance. SUM1315MO2 cells were cultured in the presence of increasing concentrations of the PARP inhibitor rucaparib or cisplatin until rucaparib resistant (RR) and cisplatin resistant (CR) clones emerged. Results: DNA sequencing revealed that no BRCA1 gene reversion mutations were present in resistant cells. We next measured BRCA1 protein levels by Western blotting with antibodies specific for the N- and C-terminal domains of BRCA1. As a control, the wild-type BRCA1 protein expressed in MDA-MB-231 cells was detectable with both N- and C-terminal antibodies. In contrast, BRCA1 protein was undetectable in both SUM1315MO2 parental and resistant clones using the N-terminal specific antibody. However, the C-terminal specific antibody identified a more quickly migrating band of low abundance in parental cells, but with elevated expression in both RR and CR clones. We inferred that this protein was devoid of the extreme N-terminal RING domain-containing region that mediates interaction with BARD1. To investigate the functionality of the N-terminal truncated BRCA1 protein (Nt-BRCA1), we measured BRCA1 and RAD51 irradiation-induced focus formation by immunofluorescence. RR and CR clones demonstrated 2.25 - 2.75-fold increase (P = 0.024) in the number of cells with BRCA1 foci compared to parental cells. Similarly, we detected a 2 - 2.85-fold increase (P = 0.0325) in RAD51 foci formation in resistant clones compared to parental cells. Additionally, BRCA1 siRNA treated cells were 12- and 9-fold more sensitive to rucaparib compared to scrambled siRNA-treated control cells (P = 0.0002). Similarly, CR-1 cells treated with BRCA1 siRNAs were 1.56- and 1.7-fold more sensitive to cisplatin (P = 0.0346) compared to scrambled siRNA treated cells. Furthermore, N-terminal truncated BRCA1 proteins were detectable in a primary tumor from a germline BRCA1185delAG mutation carrier. Conclusions: Taken together, these results provide evidence for a novel, mutation location-dependent mechanism of PARP inhibitor and platinum resistance. Citation Format: Yifan Wang, Andrea Bernhardy, Emmanuelle Nicolas, Ryan Winters, Kathy Cai, Kelly Duncan, James Duncan, Maria Harrell, Elizabeth Swisher, Neil Johnson. BRCA1 N-terminal-deficient proteins provide PARP inhibitor and platinum resistance. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5467. doi:10.1158/1538-7445.AM2015-5467