Germline variants and phenotypic spectrum in a Canadian cohort of individuals with diffuse gastric cancer.

Background: CDH1 pathogenic variants (pvs) cause most cases of inherited diffuse gastric cancer (dgc), but have low detection rates and vary geographically. In the present study, we examined hereditary causes of dgc in patients in Ontario. Methods: CDH1 testing through single-site or multi-gene panels was conducted for patients with dgc meeting the 2015 International Gastric Cancer Linkage Consortium (igclc) criteria, or with isolated dgc at less than 50 years of age, or with a strong family history of cancer identified at the Zane Cohen Centre (zcc). All CDH1-positive patients at zcc, regardless of cancer history, were summarized. Results: In 15 of 85 patients with dgc (17.6%), a pv or likely pv was identified through CDH1 single-site (n = 43) or multi-gene panel (n = 42) testing. The detection rate was 9.4% overall (8 of 85) and 11% using igclc criteria (7 of 65). No CDH1 pvs were identified in patients with isolated dgc at less than 40 years of age, but 1 pv was identified in a patient with isolated dgc at less than 50 years of age. Multi-gene panels identified 9 pvs (21.4%), including CDH1, STK11, ATM, BRCA2, MLH1, and MSH2. Review of 81 CDH1 carriers identified 10% with dgc (median age: 48 years; range: 38-59 years); 41% were unaffected (median age: 53 years; range: 26-89 years). Observed malignancies other than dgc or lobular breast cancer (lbc) included colorectal, gynecologic, kidney or bladder, prostate, testicular, and ductal breast cancers. Lobular-breast cancer was seen only in 3 families. Conclusions: In Ontario, the detection rate of CDH1 pvs in patients with dgc was low: no pvs were identified in patients with isolated dgc at less than 40 years of age, and 1 was identified in a patient with isolated dgc at less than 50 years of age. Isolated lbc with no dgc was observed in CDH1-positive families, as were pathology-confirmed nondgc or non-lbc malignancies, which had not previously been reported. Given a phenotype that overlaps with other hereditary conditions, multi-gene panels are recommended for all patients with dgc at less than 50 years of age and for those meeting igclc criteria.

Disruption of YWHAE gene at 17p13.3 causes learning disabilities and brain abnormalities.

There is a broad phenotypic spectrum of patients with 17p13.3 deletions. One of the most prominent feature is lissencephaly caused by haploinsufficiency of the gene PAFAH1B1. The deletion of this gene and those distal to it, results in Miller-Dieker syndrome, however there have been many reports of patients with haploinsufficiency of the distal genes alone. The deletions of these genes including YWHAE CRK and TUSC5 have been studied extensively and YWHAE has been postulated to be the cause of neurological abnormalities. The patients with deletions of the Miller-Dieker syndrome distal region present with variable clinical features including brain abnormalities, growth retardation, developmental delay, facial dysmorphisms and seizures. While there have been many patients reported to have deletions involving the YWHAE gene along with other genes, here we present the first detailed clinical description of a patient with deletion of YWHAE alone, allowing a more accurate characterization of the pathogenicity of YWHAE haploinsufficiency. The patient reported here demonstrated brain abnormalities, learning disabilities, and seizures supporting the role of YWHAE in these features. We review the literature and use this case report to better characterize and further confirm the genotype-phenotype relationship of the genes within the critical region of Miller-Dieker Syndrome.

Autosomal recessive hereditary spastic paraplegia-clinical and genetic characteristics of a well-defined cohort.

We describe the clinical and genetic features of a well-characterized cohort of patients with autosomal recessive hereditary spastic paraplegia (ARHSP) in the province of Ontario. Patients with documented corticospinal tract abnormalities were screened by whole gene sequencing and multiplex ligation probe amplification for mutations in nine genes known to cause ARHSP. Of a cohort of 39 patients, a genetic diagnosis was established in 17 (44 %) and heterozygous mutations were detected in 8 (21 %). Mutations were most frequent in SPG7 (12 patients), followed by SPG11 (10 patients), PNPLA6 (SPG39, 2 patients), and ZFYVE26 (SPG15, 2 patients). Although there are associations between some clinical manifestations of ARHSP and specific genes, many patients are tested at an early stage of the disease when phenotype/genotype correlations are not obvious. Accurate molecular characterization of well-phenotyped cohorts of patients will be essential to establishing the natural history of these rare degenerative disorders to enable future clinical trials.

Age at first birth and the risk of breast cancer in BRCA1 and BRCA2 mutation carriers.

An early age at first full-term birth is associated with a reduction in the subsequent development of breast cancer among women in the general population. A similar effect has not yet been reported among women who carry an inherited BRCA1 or BRCA2 mutation. We conducted a matched case-control study on 1816 pairs of women with a BRCA1 (n = 1405) or BRCA2 (n = 411) mutation in an attempt to elucidate the relationship between age at first full-term pregnancy and the risk of developing breast cancer. Information about the age at first childbirth and other pregnancy-related variables was derived from a questionnaire administered to women during the course of genetic counselling. There was no difference in the mean age at first full-term birth in the cases and controls (24.9 years vs. 24.8 years; P = 0.81, respectively). Compared to women whose first child was born at or before 18 years of age, a later age at first full-term birth did not influence the risk of developing breast cancer (OR = 1.00 per year; 95% CI 0.98-1.03; P-trend = 0.67). Stratification by mutation status did not affect the results. These findings suggest that an early first full-term birth does not confer protection against breast cancer in BRCA mutation carriers. Nonetheless, BRCA mutation carriers opting for a prophylactic oophorectomy as a breast and/or ovarian cancer risk-reducing strategy should complete childbearing prior to age 40 when this prevention modality is most effective.

Germline truncating mutations in both MSH2 and BRCA2 in a single kindred.

There has been interest in the literature in the possible existence of a gene that predisposes to both breast cancer (BC) and colorectal cancer (CRC). We describe the detailed characterisation of one kindred, MON1080, with 10 cases of BC or CRC invasive cancer among 26 first-, second- or third-degree relatives. Linkage analysis suggested that a mutation was present in BRCA2. DNA sequencing from III: 22 (diagnosed with lobular BC) identified a BRCA2 exon 3 542G>T (L105X) mutation. Her sister (III: 25) had BC and endometrial cancer and carries the same mutation. Following immunohistochemical and microsatellite instability studies, mutation analysis by protein truncation test, cDNA sequencing and quantitative real-time PCR revealed a deletion of MSH2 exon 8 in III: 25, confirming her as a double heterozygote for truncating mutations in both BRCA2 and MSH2. The exon 8 deletion was identified as a 14.9 kb deletion occurring between two Alu sequences. The breakpoint lies within a sequence of 45 bp that is identical in both Alu sequences. In this large BC/CRC kindred, MON1080, disease-causing truncating mutations are present in both MSH2 and BRCA2. There appeared to be no increased susceptibility to the development of colorectal tumours in BRCA2 mutation carriers or to the development of breast tumours in MSH2 mutation carriers. Additionally, two double heterozygotes did not appear to have a different phenotype than would be expected from the presence of a mutation in each gene alone.

Predictive, pre-natal and diagnostic genetic testing for Huntington's disease: the experience in Canada from 1987 to 2000.

Predictive and pre-natal testing for Huntington's Disease (HD) has been available since 1987. Initially this was offered by linkage analysis, which was surpassed by the advent of the direct mutation test for HD in 1993. Direct mutation analysis provided an accurate test that not only enhanced predictive and pre-natal testing, but also permitted the diagnostic testing of symptomatic individuals. The objective of this study was to investigate the uptake, utilization, and outcome of predictive, pre-natal and diagnostic testing in Canada from 1987 to April 1, 2000. A retrospective design was used; all Canadian medical genetics centres and their affiliated laboratories offering genetic testing for HD were invited to participate. A total of 15 of 22 centres (68.2%), currently offering or ever having offered genetic testing for HD, responded, providing data on test results, demographics, and clinical history. A total of 1061 predictive tests, 15 pre-natal tests, and 626 diagnostic tests were performed. The uptake for predictive testing was approximately 18% of the estimated at-risk Canadian population, ranging from 12.5% in the Maritimes to 20.7% in British Columbia. There appears to have been a decline in the rate of testing in recent years. Of the predictive tests, 45.0% of individuals were found to have an increased risk, and a preponderance of females (60.2%) sought testing. A greater proportion of those at < or = 25% risk sought predictive testing once direct CAG mutation analysis had become available (10.9% after mutation analysis vs 4.7% before mutation analysis, p = 0.0077). Very few pre-natal tests were requested. Of the 15 pre-natal tests, 12 had an increased risk, resulting in termination of pregnancy in all but one. Diagnostic testing identified 68.5% of individuals to be positive by mutation analysis, while 31.5% of those with HD-like symptoms were not found to have the HD mutation. The positive diagnostic tests included 24.5% of individuals with no known prior family history of HD.

Ethical, legal, and practical concerns about recontacting patients to inform them of new information: the case in medical genetics.

There is a consensus among medical geneticists that it is desirable to recontact patients as new information becomes available. Furthermore, some have suggested that there are legal arguments to support an obligation, creating a duty to recontact. Thus far much of the discussion among medical geneticists has focused on the practical concerns of implementing such a policy. However, we think that any such policy raises a number of important ethical concerns that must first be considered. Furthermore, there has not been a careful evaluation of the legal precedents that may reflect on a hypothetical duty to recontact. In this paper we first present an analysis of the scope of approaches and issues to be addressed in the development of ethical policy on this question. Secondly, we examine whether there is a legal obligation to recontact former patients about advances in genetics, as well as the legal implications if such a policy were to be adopted. Finally, we consider some of the functional and resource implications of adopting a policy of recontact. Our goal is to provide a framework for further discussion of this question and to stimulate further debate and research.

Screening for PS1 mutations in a referral-based series of AD cases: 21 novel mutations.

BACKGROUND: Mutations in the presenilin-1 gene (PS1) account for a majority of patients with early-onset familial AD. However, the clinical indications and algorithms for genetic testing in dementia are still evolving. METHODS: The entire open reading frame of the PS1 gene was sequenced in a series of 414 consecutive patients referred for diagnostic testing, including 372 patients with AD and 42 asymptomatic persons with a strong family history of AD. RESULTS: Forty-eight independent patients screened had a PS1 mutation including 21 novel mutations. In addition, 3% of subjects (11/413) had a known polymorphism, the Glu318Gly substitution. The majority of the mutations were missense substitutions but there were three insertions and Delta exon 10 mutation. With six exceptions (codons 35, 178, 352, 354, 358, and 365) most of the mutations occurred at residues conserved in the homologous PS2 gene or in PS1 of other species. CONCLUSIONS: Eleven percent of a referral-based series of patients with AD can be explained by coding sequence mutations in the PS1 gene. The high frequency of PS1 mutations in this study indicates that screening for PS1 mutations in AD is likely to be successful, especially when directed at patients with a positive family history with onset before 60 years (90% of those with PS1 mutations were affected by age 60 years). This will also have significance for the secondary identification of at-risk relatives who might be candidates for future prophylactic therapies for AD.

Psychosocial issues following a positive result of genetic testing for BRCA1 and BRCA2 mutations: findings from a focus group and a needs-assessment survey.

BACKGROUND: About 5% of cases of breast cancer and 10% of cases of ovarian cancer are due to an inherited predisposition. Since 1994 it has been possible to test some people at high risk for inherited mutations to the BRCA1 and BRCA2 genes. The purpose of our study was to explore how genetic testing had affected people found to have a BRCA mutation and their families, and to determine whether there was interest in a peer-support group. METHODS: All people given positive results of genetic testing for BRCA1 and BRCA2 mutations at either of 2 familial breast cancer clinics were invited to participate in a focus group and complete a questionnaire. Those who did not attend or who received positive results after the focus group were mailed the questionnaire. Information was sought on the effect of testing on cancer risk perception and worry about cancer, communication of test results to family members, attitudes toward surveillance and toward prevention options, satisfaction with clinical services, need for additional support and satisfaction with decision to undergo testing. RESULTS: Eight of the 27 people invited to participate in the focus group attended. Sixteen of the 26 who were mailed the questionnaire completed and returned it. Although cancer risk perception and worry increased after receipt of the test results, the participants did not regret their decision to undergo testing. Confidence in the efficacy of cancer surveillance was high. Prophylactic oophorectomy was much more acceptable than prophylactic mastectomy. Almost all (92% [22/24]) were satisfied with the clinical services they had received; however, all were dissatisfied with the lengthy wait for test results. Nine (38%) of the participants felt they would benefit from a support group. INTERPRETATION: Adequate resources must be made available to clinical programs providing BRCA1 and BRCA2 mutation testing to ensure appropriate pretest counselling and timely availability of results. Organization of support groups for people found to have the gene mutations should be a priority for these programs.

Perceptions of Ashkenazi Jewish breast cancer patients on genetic testing for mutations in BRCA1 and BRCA2.

The perceived benefits and risks of genetic testing may vary between groups of individuals with different cultural, demographic, and family history features. This multicentre study examined the factors that influenced the decision to undergo genetic testing for BRCA1 and BRCA2 in Canadian Jewish women with breast cancer. A self-administered questionnaire was developed and distributed to 134 individuals enrolled in a research-based testing program for Ashkenazi women. The questionnaire assessed demographic, social, and family history parameters, and the influence of medical, family, social, psychological, and cultural/religious factors on decision making about genetic testing. Seventy-six percent of women completed the questionnaire. Forty-one percent of study participants had no family history of breast or ovarian cancer. The most important factors influencing the decision to undergo testing were a desire to contribute to research, potential benefit to other family members, curiosity, and the potential for relief if not found to be a carrier (endorsed by 87, 78, 70, and 60% of participants, respectively). The main perceived risks of undergoing genetic testing related to insurance discrimination, confidentiality, accuracy and interpretability of results, potential impact on marriage prospects for family members, and focus on the Jewish community (endorsed by 28, 24, 30, 17, and 14% of participants, respectively). This study provides novel information on the motivating factors for BRCA1 and BRCA2 mutation testing in Canadian women of Ashkenazi Jewish descent. The focus on altruistic factors and those related to perceived psychological benefits of testing is notable.

Endoglin expression is reduced in normal vessels but still detectable in arteriovenous malformations of patients with hereditary hemorrhagic telangiectasia type 1.

Endoglin is predominantly expressed on endothelium and is mutated in hereditary hemorrhagic telangiectasia (HHT) type 1 (HHT1). We report the analysis of endoglin in tissues of a newborn (family 2), who died of a cerebral arteriovenous malformation (CAVM), and in a lung specimen surgically resected from a 78-year-old patient (family 5), with a pulmonary AVM (PAVM). The clinically affected father of the newborn revealed a novel mutation that was absent in his parents and was identified as a duplication of exons 3 to 8, by quantitative multiplex polymerase chain reaction. The corresponding mutant protein (116-kd monomer) and the missense mutant protein (80-kd monomer) present in family 5 were detected only as transient intracellular species and were unreactive by Western blot analysis and immunostaining. Normal endoglin (90-kd monomer) was reduced by 50% on peripheral blood-activated monocytes of the HHT1 patients. When analyzed by immunostaining and densitometry, presumed normal blood vessels of the newborn lung and brain and vessels adjacent to the adult PAVM showed a 50% reduction in the endoglin/PECAM-1 ratio. A similar ratio was observed in the CAVM and PAVM, suggesting that all blood vessels of HHT1 patients express reduced endoglin in situ and that AVMs are not attributed to a focal loss of endoglin.

Molecular mechanism for duplication 17p11.2- the homologous recombination reciprocal of the Smith-Magenis microdeletion.

Recombination between repeated sequences at various loci of the human genome are known to give rise to DNA rearrangements associated with many genetic disorders. Perhaps the most extensively characterized genomic region prone to rearrangement is 17p12, which is associated with the peripheral neuropathies, hereditary neuropathy with liability to pressure palsies (HNPP) and Charcot-Marie-Tooth disease type 1A (CMT1A;ref. 2). Homologous recombination between 24-kb flanking repeats, termed CMT1A-REPs, results in a 1.5-Mb deletion that is associated with HNPP, and the reciprocal duplication product is associated with CMT1A (ref. 2). Smith-Magenis syndrome (SMS) is a multiple congenital anomalies, mental retardation syndrome associated with a chromosome 17 microdeletion, del(17)(p11.2p11.2) (ref. 3,4). Most patients (>90%) carry deletions of the same genetic markers and define a common deletion. We report seven unrelated patients with de novo duplications of the same region deleted in SMS. A unique junction fragment, of the same apparent size, was identified in each patient by pulsed field gel electrophoresis (PFGE). Further molecular analyses suggest that the de novo17p11.2 duplication is preferentially paternal in origin, arises from unequal crossing over due to homologous recombination between flanking repeat gene clusters and probably represents the reciprocal recombination product of the SMS deletion. The clinical phenotype resulting from duplication [dup(17)(p11.2p11.2)] is milder than that associated with deficiency of this genomic region. This mechanism of reciprocal deletion and duplication via homologous recombination may not only pertain to the 17p11.2 region, but may also be common to other regions of the genome where interstitial microdeletion syndromes have been defined.

Prevalence and penetrance of BRCA1 and BRCA2 gene mutations in unselected Ashkenazi Jewish women with breast cancer.

BACKGROUND: Approximately 2.0%-2.5% of Ashkenazi Jewish women carry one of three founding mutations in the BRCA1 and BRCA2 genes, and each mutation is associated with a high lifetime risk of invasive breast cancer. We investigated the extent to which these three mutations contribute to breast cancer incidence in the Ashkenazi Jewish population. METHODS: We ascertained 457 Jewish women with prevalent cases of breast cancer who were unselected for age or family history of the disease; 412 of these women were tested for the three founder mutations (case patients). Control subjects consisted of 360 non-Jewish women with breast cancer (control patients) and 380 healthy Jewish women with no history of cancer (control subjects). RESULTS: Mutations were found in 48 (11.7%) of 412 Jewish case patients. Forty-six of 48 mutations occurred in women with early-onset breast cancer (<50 years) or a history of ovarian or early-onset breast cancer in a first-, second-, or third-degree relative. The estimated penetrance to age 70 years for breast cancer was 59.9% for the BRCA1 gene mutations and 28.3% for the BRCA2 gene mutation. Compared with Jewish control subjects, the relative risk (RR) of breast cancer for first-degree relatives of mutation carriers was 5.16 (95% confidence interval [CI] = 3.14-8. 48), but risk was also increased for relatives of noncarriers (RR = 1.66; 95% CI = 1.18-2.33). The RR of prostate cancer for first-degree relatives of Jewish case patients was 3.36 (95% CI = 1. 49-7.56). CONCLUSIONS: Approximately 12% of breast cancers in the Ashkenazi Jewish population are attributable to mutations in the BRCA1 or BRCA2 gene. Genetic testing may be useful when Jewish women with breast cancer are diagnosed before age 50 years or have a close relative with ovarian or early-onset breast cancer. An association between breast and prostate cancers was observed in our study population.

Aberrant splicing in the presenilin-1 intron 4 mutation causes presenile Alzheimer's disease by increased Abeta42 secretion.

We previously described a splice donor site mutation in intron 4 of presenilin-1 (PSEN1) in two patients with autopsy-confirmed early-onset Alzheimer's disease (AD). Here we provide evidence that the intron 4 mutation is present in four additional unrelated early-onset AD cases, that the mutation segregates in an autosomal dominant manner and that all cases have one common ancestor. We demonstrate that the intron 4 mutation produces three different transcripts, two deletion transcripts (Delta4 and Delta4cryptic) and one insertion transcript (insTAC), by aberrant splicing. The deletion transcripts result in the formation of C-truncated (approximately 7 kDa) PSEN1 proteins while the insertion transcript produces a full-length PSEN1 with one extra amino acid (Thr) inserted between codons 113 and 114 (PSEN1 T113-114ins). The truncated proteins were not detectable in vivo in brain homogenates or lymphoblast lysates of mutation carriers. In vitro HEK-293 cells overexpressing Delta4, Delta4cryptic or insTACPSEN1 cDNAs showed increased Abeta42 secretion (approximately 3.4 times) only for the insertion cDNA construct. Increased Abeta42 production was also observed in brain homogenates. Our data indicate that in the case of intron 4 mutation, the AD pathophysiology results from the presence of the PSEN1 T113-114ins protein comparable with cases carrying dominant PSEN1 missense mutations.

Schimke immunoosseous dysplasia complicated by moyamoya phenomenon.

Schimke immunoosseous dysplasia (SID) is an autosomal recessive spondyloepiphyseal dysplasia that was first described by Schimke et al. [1971: Lancet 2:1088-1089]. It is associated with premature arteriosclerosis and cerebral ischemia; however, the cerebral vascular abnormalities causing ischemia have not been described [Spranger et al., 1991: J Pediatr 119:64-72; Ehrich et al., 1995: Clin Nephrol 43:89-95]. Based on magnetic resonance angiography (MRA) and magnetic resonance venography (MRV), we now report on 2 girls with SID who have cerebral ischemia associated with moyamoya phenomenon. In addition, one patient also has an absent or occluded left transverse sinus and diffuse aortic narrowing. This is the first characterization of the cerebral vascular abnormality found in SID and raises the possibility that cerebral moyamoya may represent another major manifestation of the underlying genetic defect in SID.

Risk reversals in predictive testing for Huntington disease.

The first predictive testing for Huntington disease (HD) was based on analysis of linked polymorphic DNA markers to estimate the likelihood of inheriting the mutation for HD. Limits to accuracy included recombination between the DNA markers and the mutation, pedigree structure, and whether DNA samples were available from family members. With direct tests for the HD mutation, we have assessed the accuracy of results obtained by linkage approaches when requested to do so by the test individuals. For six such individuals, there was significant disparity between the tests. Three went from a decreased risk to an increased risk, while in another three the risk was decreased. Knowledge of the potential reasons for these changes in results and impact of these risk reversals on both patients and the counseling team can assist in the development of strategies for the prevention and, where necessary, management of a risk reversal in any predictive testing program.

New point mutations and deletions of the connexin 32 gene in X-linked Charcot-Marie-Tooth neuropathy.

The purpose of this study was the identification of new mutations of the connexin 32 (CX32) gene in CMTX families. We report six new mutations of the CX32 gene including two medium sized (29 and 18 bp) deletions. The clinical phenotype is consistent with CMT peripheral neuropathy in all patients. Four families show both male and female patients, with more severe symptoms in males. The disease is asymptomatic in females in two families. The clinical deficit in CMTX families Nos 1, 2 and 4 with missense mutations of the CX32 gene was mild or moderate. Severe weakness of the feet and hands was present in CMTX family No. 5 with a G insertion and family No. 6 with a 29 bp deletion in the carboxyl terminal region of the CX32 gene. Most likely the severe clinical impact in those families was related to frame shift and premature termination of the protein.

Linkage analysis of the nail-patella syndrome.

Nail-patella syndrome (NPS) is an autosomal dominant disorder characterized by dysplasia of nails and patella, decreased mobility of the elbow, iliac horns, and, in some cases, nephropathy. The disorder has been mapped to the long arm of chromosome 9, but the precise localization and identity of the NPS gene are unknown. Linkage analysis in three NPS families, using highly informative dinucleotide repeat polymorphisms on 9q33-q34, confirmed linkage of NPS to this chromosome. Recombinations were detected, by two-point linkage analysis, between NPS and the centromeric markers D9S60 and the gelsolin gene and the telomeric markers D9S64 and D9S66, in one of the families. Haplotype analysis suggested an additional recombination between NPS and the argininosuccinate synthetase (ASS) gene. These results localize the NPS gene to an interval on 9q34.1, distal to D9S60 and proximal to ASS, comprising a genetic distance of approximately 9 cM. This represents a significant refinement in the localization of the NPS gene.