Presymptomatic Testing Research Articles

Uptake of Huntington disease predictive testing in a complete population

Using the Northern Ireland Huntington disease (HD) register, the number of prospectively recorded predictive tests was analysed over a 20-year period. Two hundred and twelve patients completed predictive testing. Ninety-two (43%) received mutation-positive results and 119 (56%) mutation negative. There was one intermediate allele result. There was no significant gender difference. One hundred and eighty affected cases confirmed by molecular genetic testing were alive on 1 January 2001. The uptake of predictive testing in the entire HD 50% at-risk population in 2001 was calculated by three methods giving a range of 12.3-14.6%. Uptake after 20 years was estimated to be 14.7%. The minimum prevalence of affected HD cases was calculated as 10.6/100,000 in 2001. The total uptake of predictive testing was calculated and it suggests that a substantial number of at-risk patients do not come forward for testing until symptomatic. Pre-symptomatic testing for this late-onset condition with no present treatment, and limited management options, still presents challenges for families.

Large normal and reduced penetrance alleles in Huntington disease: instability in families and frequency at the laboratory, at the clinic and in the population

Large normal ('intermediate') alleles may produce de novo expansions in Huntington disease; nevertheless, there is very little evidence about their population prevalence and impact in daily practice, and there are conflicting reports about the extent of their instability. We estimated the frequency of large normal alleles (27-35 CAGs) and of reduced penetrance alleles (36-39 CAGs), as well as the frequency of genotypes carrying them, in (i) a diagnostic laboratory, (ii) a genetic counselling clinic and (iii) the general population. Large normal alleles were present in 6% of a large control sample, 7% of consultands who took pre-symptomatic testing and 7% of samples in the laboratory. Reduced penetrance alleles were found in 1 of 1772 control chromosomes (0.1% of individuals), 5% of 146 pre-symptomatic testees and over 2% of 1214 diagnostic samples (350 families). All 16 alleles sized 27-32 CAGs seemed to be transmitted stably; alleles ≥ 36 repeats were unstable in five families. Seven small full penetrance alleles contracted into the reduced penetrance range, but none into the large normal range. Evidence showed that large normal alleles are relatively frequent and that those with reduced penetrance are not a rare event, either at the laboratory or the clinic. This reinforces the need to understand the genomic context of repeat instability in each family and population.

Validation of Sensitivity and Specificity of Tetraplet-Primed PCR (TP-PCR) in the Molecular Diagnosis of Myotonic Dystrophy Type 2 (DM2)

Myotonic dystrophy type 2 (DM2, OMIM #602688) is a multisystemic hereditary degenerative disease caused by a tetranucleotide CCTG expansion in the ZNF9 gene. Routine testing strategies for DM2 require the use of Southern blot or long-range PCR, but the presence of very large expansions and wide somatic mosaicism greatly reduce the sensitivity of these reference techniques. We therefore developed and validated a tetraplet-primed PCR (TP-PCR) method to detect the DM2 mutation by testing 87 DM2-positive and 76 DM2-negative previously characterized patients. The specificity of this technique was evaluated including DNA samples from 39 DM1-positive patients. We then attempted a prospective analysis of 50 patients with unknown genotype who referred to our center for diagnostic or presymptomatic tests. Results show that TP-PCR is a fast, reliable, and flexible technique, whose specificity and sensitivity is almost 100%, with no false positive or negative results either in retrospective and prospective applications. We therefore conclude that using this technique, in combination with the short-range PCR, is sufficient to correctly establish the presence or the absence of ZNF9 expanded alleles in the molecular diagnosis of DM2.

D03 Prenatal diagnosis after presymptomatic testing for Huntington's disease: attitudes, decision making and emotional outcome

Feedback on the procedure, staff, emotional outcome and reproductive decisions is important for genetic counselling in Huntington's disease (HD). A standardised telephone interview was done to 12 couples who had...

D01 Updating of guidelines for the molecular genetic predictive test in Huntington's disease (1994)

BackgroundGuidelines for the molecular genetic predictive testing in Huntington's disease (HD) were issued in 1994, soon after the discovery of the gene. Since then, the research on HD has made...

Informing family members about a hereditary predisposition to cancer: attitudes and practices among clinical geneticists

If a hereditary predisposition to colorectal cancer or breast cancer is diagnosed, most guidelines state that clinical geneticists should request index patients to inform their at-risk relatives about the existence...

Genetic Testing in Li-Fraumeni Syndrome: Uptake and Psychosocial Consequences

Li-Fraumeni syndrome (LFS) is a hereditary cancer syndrome, characterized by a high risk of developing cancer at various sites and ages. To date, limited clinical benefits of genetic testing for LFS have been demonstrated, and there are concerns about the potential adverse psychosocial impact of genetic testing for LFS. In this study, we evaluated the uptake of genetic testing and the psychosocial impact of undergoing or not undergoing a genetic test for LFS. In total, 18 families with a p53 germline mutation in the Netherlands were identified. Eligible family members were invited to complete a self-report questionnaire assessing motives for undergoing or not undergoing genetic testing, LFS-related distress and worries, and health-related quality of life. Uptake of presymptomatic testing was 55% (65 of 119). Of the total group, 23% reported clinically relevant levels of LFS-related distress. Carriers were not significantly more distressed than noncarriers or than those with a 50% risk who did not undergo genetic testing. Those with a lack of social support were more prone to report clinically relevant levels of distress (odds ratio, 1.3; 95% CI, 1.0 to 1.5). Although preventive and treatment options for LFS are limited, more than half of the family members from known LFS families choose to undergo presymptomatic testing. An unfavorable genetic test result, in general, does not cause adverse psychological effects. Nonetheless, it is important to note that a substantial proportion of individuals, irrespective of their carrier status, exhibit clinically relevant levels of distress which warrant psychological support.

Low penetrance of a SDHB mutation in a large Dutch paraganglioma family

BackgroundGermline mutations of the succinate dehydrogenase subunit B gene (SDHB) predispose carriers for paragangliomas, and current estimates of the chance of mutation carriers actually developing tumors (penetrance) are high. We evaluate the phenotype and penetrance of a germline SDHB mutation in a large and clinically well-characterized paraganglioma family.MethodsFollowing identification of the mutation in a 31 year old index-patient, extensive clinical screening was performed in mutation carriers to evaluate the presence of head and neck, thoracic and abdominal paragangliomas. Presymptomatic DNA testing was performed in 19 family members.ResultsDNA analysis detected 14 further SDHB mutation carriers. Three mutation carriers (median age 78 years) declined clinical surveillance, but had no clinical signs or symptoms associated with paragangliomas. The remaining 11 mutation carriers (mean age 53, range 37-76 years) consented to clinical screening. In only two, aged 43 and 48 years, were subclinical vagal paragangliomas identified.ConclusionsOnly three of the fifteen mutation carriers in this family have developed paraganglioma, which results in a calculated penetrance of 26% at 48 years of age. This figure is lower than current estimates, and we conclude that the co-operation of this family allowed an almost complete attainment of mutation carriers, and the extensive clinical evaluation carried out allowed us to identify all affected individuals.

Cell-Based Screening Test for Idiopathic Scoliosis Using Cellular Dielectric Spectroscopy

A cell-based assay was developed to identify asymptomatic children at risk of developing idiopathic scoliosis (IS) and to stratify IS patients at an earlier stage in order to better predict their clinical outcome. Clinical validation of this assay was performed by testing IS patients at different stages, healthy control subjects, and asymptomatic offspring, born from at least one scoliotic parent, who are considered at risk of developing this disorder. Our goal was to develop and validate a clinical test for IS using cellular dielectric spectroscopy (CDS) and peripheral blood mononuclear cells (PBMCs). We have previously demonstrated the occurrence of a melatonin signaling dysfunction in osteoblasts obtained from severely affected IS patients using a cAMP assay. This led us to stratify IS patients into 3 functional subgroups. A group of 44 patients with IS was compared with 42 healthy control subjects and 31 asymptomatic at-risk children. PBMCs were obtained after centrifugation on a Ficoll-gradient. Melatonin signal transduction was measured by CDS in the presence of varying concentrations of melatonin or iodomelatonin. Osteoblasts from distinct functional subgroups were retested using CDS, allowing their classification into the same functional subgroups with both ligands as initially demonstrated using a cAMP assay. Clinical data obtained with CDS and PBMCs showed 100% specificity and 100% sensitivity because melatonin signaling impairment was observed only in IS patients and not in healthy controls. Assessment of the risk of developing a scoliosis in asymptomatic children was determined by CDS in 33% of asymptomatic children at risk, which was confirmed clinically within 24 months. This cell-based assay can serve as a presymptomatic screening test to identify asymptomatic children at risk of developing IS and may be used to improve stratification of patients, which in turn allow clinicians to predict their clinical outcome. Moreover, this functional blood test is advantageous because it can be performed without prior knowledge of specifically mutated genes causing IS.

Advances in the Genetics of Familial Renal Cancer

We discuss recent advances in the diagnosis and management of renal cell cancer (RCC) given the enhanced molecular genetics knowledge in this area. A number of hereditary renal cancer syndromes have been described, including von Hippel-Lindau disease, Birt-Hogg-Dubé syndrome, hereditary leiomyomatosis/RCC syndrome, and hereditary papillary renal cancer. Early molecular diagnosis now facilitates the management and prevention of RCC in families. Recommendations for screening in families are discussed.

Accrual Strategies for Cancer Genetics Research: Blurred Boundaries

and BRCA2 founder mutations in an unselected group of Ashkenazi Jewish women, with an astounding 2,000 women enrolled within 14 days of an article appearing in one of Canada’s most respected newspapers. Given the overwhelming interest among the target population, one might ask exactly what information prompted such an overwhelming response. The article in question was published on the front page of the Toronto Globe and Mail (Saturday May 24, 2008) with a large-font headline reading: “Cancer test a genetic crystal ball for Jewish women.” 2 The first line in the piece stated: “For the first time in Canada, Jewish women will be offered the chance to alter their genetic destiny by taking a test…” a patently untrue and sensationalistic statement, given that presymptomatic BRCA1 and BRCA2 mutation testing, including Ashkenazi Jewish founder mutations, have been available for many years through medical genetics services nationwide. The concept of altering genetic destiny remains a potentially very desirable goal for those at real or perceived risk but is highly problematic in the clinical setting as any involved with the provision of genetic and oncologic care can easily attest. The goal of the test was “to prevent cancer” as elucidated by one of the investigators in the article. Two rabbis were quoted, the first commenting that “The rate of the gene is so high, it will be one of the tests that is normally done,” equatingBRCA1 and-2 testing to screening for Tay-Sachs, a culturally specific heritable disease. The other stated that genetic testing was a no-brainer imputing Halacha (Jewish law) that “insists that one is obligated to take care of oneself” as rationale for testing. Risks of taking the test are described as “primarily psychological, such as depression and stress, or unpredicted implications for obtaining life or critical care insurance.” Although the authors note a number of limitations to their work, the ethical implications are not mentioned. How sensationalistic is a headline allowed to be in order to generate accrual to a research study? How appropriate is it to imbibe the research with culturally and religiously significant implications directly aimed at the ethnic group under investigation? How justified is it to minimize the potential emotional angst and psychological turmoil that genetic testing can engender for subjects and their families? What degree of overstatement can be accepted when describing bothBRCA mutation incidence as well as the evidence of benefit from testing, when approaching a susceptible population for research purposes? With the goal of the research summarized as “to prevent cancer,” along with supporting patient vignettes, religious calls to action, and minimization of the clinical, psychological and emotional dilemmas faced by all those undergoing genetic testing, who could resist making the call to enroll in the study? Although the potential benefits of presymptomatic BRCA1 and -2 mutation detection can be significant, the clinical, ethical, and emotional dilemmas surrounding genetic testing for hereditary cancer syndromes can be even more so. The recent American Society of Clinical Oncology policy statement update regarding genetic and genomic testing for cancer susceptibility 3 elucidates evolving concerns regarding direct-to-consumer genetic testing, which have relevance for both industry and academia.

Les tests génétiques présymptomatiques chez le mineur : enquête auprès des généticiens français et position du groupe français de génétique prédictive

Since their introduction, genetic tests have been carefully considered, with special attention to the release of information about the test and test results, the confidentiality of genetic information, the request and its motivation, and the psychological impact of the test. Careful consideration is needed when family members at risk are asymptomatic children or adolescents. Cautious reflection is warranted on whether and under which conditions genetic testing should be performed. Here, we report on the results of a survey conducted in France among 50 geneticists questioned on their opinions and practices concerning presymptomatic testing in three groups of diseases: those for which a medical benefit exists during childhood (e.g., retinoblastoma), diseases with onset during childhood for which there are no immediate medical consequences (e.g., type II/III spinal muscular atrophy), and those with onset during adulthood for which there is no medical benefit during childhood (e.g., Huntington disease). Guidelines are proposed: presymptomatic testing should not be performed in a minor without individual and direct information, all requests for presymptomatic genetic testing concerning a disease with onset in adulthood should be postponed, and all presymptomatic test requests for a minor should be addressed to a multidisciplinary team.

Survival Analysis on Pedigrees: A Marked Point Process Model

AbstractRegulation of insurers' use of genetic information means actuaries are interested in age-at-onset of genetic disorders. Arjas & Haara (1984) suggested marked point processes (MPPs) as useful models for life history data with complex covariates. Age-at-onset distributions (or equivalently, hazard rates) in respect of inherited disorders are often estimated from pedigrees, which are life histories with unusually complex covariates, as well as strong dependencies induced by shared genes. Since Elston (1973) parametric models have often been used, conditioning the likelihood on known genotypes. However, a genotype identii ed by a presymptomatic genetic test is a form of internal covariate (Kalbfleisch & Prentice, 2002). We propose a very general MPP model of a pedigree, including presymptomatic genetic testing, (‘the full model’) and show under what circumstances the partial model leading to Elston's likelihood is valid. In practice, pedigrees are often ascertained retrospectively. Many such events can be modelled by augmenting the natural filtration of the MPP. We show that, except in simple special cases, the partial model is no longer valid, and the resulting likelihoods appear to be intractable. In particular, ascertainment interacts even with independent censoring so that likelihoods no longer factorize. For one simple special case — studies of sibships — we generalise a classical result to age-at-onset data. We conclude that the study of genetic conditions with variable age at onset gains insights from the underlying principles of survival analysis in their modern form, but that great care is needed in translating epidemiological studies into actuarial models.

Overlapping spectra of SMAD4 mutations in juvenile polyposis (JP) and JP–HHT syndrome

Juvenile polyposis (JP) and hereditary hemorrhagic telangiectasia (HHT) are clinically distinct diseases caused by mutations in SMAD4 and BMPR1A (for JP) and endoglin and ALK1 (for HHT). Recently, a combined syndrome of JP-HHT was described that is also caused by mutations in SMAD4. Although both JP and JP-HHT are caused by SMAD4 mutations, a possible genotype:phenotype correlation was noted as all of the SMAD4 mutations in the JP-HHT patients were clustered in the COOH-terminal MH2 domain of the protein. If valid, this correlation would provide a molecular explanation for the phenotypic differences, as well as a pre-symptomatic diagnostic test to distinguish patients at risk for the overlapping but different clinical features of the disorders. In this study, we collected 19 new JP-HHT patients from which we identified 15 additional SMAD4 mutations. We also reviewed the literature for other reports of JP patients with HHT symptoms with confirmed SMAD4 mutations. Our combined results show that although the SMAD4 mutations in JP-HHT patients do show a tendency to cluster in the MH2 domain, mutations in other parts of the gene also cause the combined syndrome. Thus, any mutation in SMAD4 can cause JP-HHT. Any JP patient with a SMAD4 mutation is, therefore, at risk for the visceral manifestations of HHT and any HHT patient with SMAD4 mutation is at risk for early onset gastrointestinal cancer. In conclusion, a patient who tests positive for any SMAD4 mutation must be considered at risk for the combined syndrome of JP-HHT and monitored accordingly.

Uptake of genetic testing and long-term tumor surveillance in von Hippel-Lindau disease.

Backgroundvon Hippel-Lindau (VHL) disease is a hereditary cancer syndrome caused by germline mutations in the VHL gene. Patients have significant morbidity and mortality secondary to vascular tumors. Disease management is centered on tumor surveillance that allows early detection and treatment. Presymptomatic genetic testing is therefore recommended, including in at-risk children.MethodsWe tested 17 families (n = 109 individuals) for VHL mutations including 43 children under the age of 18. Personalized genetic counseling was provided pre and post-test and the individuals undergoing presymptomatic testing filled out questionnaires gathering socio-demographic, psychological and psychiatric data. Mutation analysis was performed by direct sequencing of the VHL gene. Mutation-carriers were screened for VHL disease-related tumors and were offered follow-up annual examinations.ResultsMutations were identified in 36 patients, 17 of whom were asymptomatic. In the initial screening, we identified at least one tumor in five of 17 previously asymptomatic individuals. At the end of five years, only 38.9% of the mutation-carriers continued participating in our tumor surveillance program. During this time, 14 mutation carriers developed a total of 32 new tumors, three of whom died of complications. Gender, education, income, marital status and religiosity were not found to be associated with adherence to the surveillance protocol. Follow-up adherence was also independent of pre-test depression, severity of disease, or number of affected family members. The only statistically significant predictor of adherence was being symptomatic at the time of testing (OR = 5; 95% CI 1.2 - 20.3; p = 0.02). Pre-test anxiety was more commonly observed in patients that discontinued follow-up (64.7% vs. 35.3%; p = 0.01).ConclusionsThe high initial uptake rate of genetic testing for VHL disease, including in minors, allowed the discontinuation of unnecessary screening procedures in non mutation-carriers. However, mutation-carriers showed poor adherence to long-term tumor surveillance. Therefore, many of them did not obtain the full benefit of early detection and treatment, which is central to the reduction of morbidity and mortality in VHL disease. Studies designed to improve adherence to vigilance protocols will be necessary to improve treatment and quality of life in patients with hereditary cancer syndromes.

Translational Research in Genomics of Alzheimer's Disease: A Review of Current Practice and Future Perspectives

Alzheimer's disease (AD) is the most prevalent form of dementia and the number of cases is expected to increase exponentially worldwide. Three highly penetrant genes (AbetaPP, PSEN1, and PSEN2) explain only a small number of AD cases with a Mendelian transmission pattern. Many genes have been analyzed for association with non-Mendelian AD, but the only consistently replicated finding is APOE. At present, possibilities for prevention, early detection, and treatment of the disease are limited. Predictive and diagnostic genetic testing is available only in Mendelian forms of AD. Currently, APOE genotyping is not considered clinically useful for screening, presymptomatic testing, or clinical diagnosis of non-Mendelian AD. However, clinical management of the disease is expected to benefit from the rapid pace of discoveries in the genomics of AD. Following a recently developed framework for the continuum of translation research that is needed to move genetic discoveries to health applications, this paper reviews recent genetic discoveries as well as translational research on genomic applications in the prevention, early detection, and treatment of AD. The four phases of translation research include: 1) translation of basic genomics research into a potential health care application; 2) evaluation of the application for the development of evidence-based guidelines; 3) evaluation of the implementation and use of the application in health care practice; and 4) evaluation of the achieved population health impact. Most research on genome-based applications in AD is still in the first phase of the translational research framework, which means that further research is still needed before their implementation can be considered.

The occurrence of spinocerebellar ataxias caused by dynamic mutations in Polish patients

Background and purposeAutosomal dominant spinocerebellar ataxias (SCAs) belong to a group of neurodegenerative disorders usually of adult age at onset. Predominant clinical features are progressive ataxia, dysarthria, as well as pyramidal signs and polyneuropathy. Molecular analysis allows particular types of SCA to be distinguished. Genetic tests are applied in 10 types of SCA resulting from dynamic mutations: SCA1, SCA2, SCA3, SCA6, SCA7, SCA8, SCA10, SCA12, SCA17 and DRPLA. Material and methodsDNA samples from 1598 patients with ataxia symptoms were analysed to establish the number of CAG/CTG repeats in respective genes excluding SCA10. ResultsWe diagnosed 224 cases of SCA1 (120 families) and 49 cases of SCA2 (23 families). Moreover, presymptomatic testing was done in 85 individuals from SCA1 families and for 21 cases from SCA2 families. An increased number of CTG repeats in the SCA8 gene was observed in 14 families and in 3 families a rare type of SCA, SCA17, was detected. ConclusionsOur data suggest that frequencies of some types of SCA in Poland are different from those in other European countries, with irregular distribution within the country. The most frequent types are SCA1 and SCA2. A striking feature of the Polish population is the lack of SCA3 – the most frequent type in Western Europe.

Molecular testing for adult type Alport syndrome

BackgroundAlport syndrome (AS) is a progressive renal disease with cochlear and ocular involvement. The majority of AS cases are X-linked (XLAS) and due to mutations in the COL4A5 gene. Although the disease may appear early in life and progress to end stage renal disease (ESRD) in young adults, in other families ESRD occurs in middle age. Few of the more than four hundred mutations described in COL4A5 are associated with adult type XLAS, but the families may be very large.MethodsWe classified adult type AS mutation by prevalence in the US and we developed a molecular assay using a set of hybridization probes that identify the three most common adult type XLAS mutations; C1564S, L1649R, and R1677Q.ResultsThe test was validated on samples previously determined to contain one or none of these mutations. In the US, the test's clinical specificity and sensitivity are estimated to be higher than 99% and 75% respectively. Analytical specificity and sensitivity are above 99%.ConclusionThis test may be useful for presymptomatic and carrier testing in families with one of the mutations and in the diagnosis of unexplained hematuria or chronic kidney disease.

Genetic Counselors’ Perceived Responsibilities Regarding Reproductive Issues for Patients at Risk for Huntington Disease

Research indicates that health care professionals' attitudes may affect patients' decisions regarding prenatal Huntington Disease testing, but few studies have sampled genetic counselors. In this qualitative study, genetic counselors described their experiences counseling individuals at risk for HD regarding reproductive decision-making. Five major research questions were investigated: 1) What are genetic counselor responsibilities? 2) What issues arise for patients and counselors? 3) How do counselors reconcile prenatal testing with presymptomatic testing? 4) To what extent are counselors' initial expectations of at-risk patients' beliefs and behaviors met? and 5) What advice would counselors offer to novice practitioners about working with this patient population? Fifteen genetic counselors experienced in counseling individuals at risk for HD participated in a semi-structured phone interview that yielded several themes. For example, participants identified their primary responsibility as information provision; less prevalent were psychosocial support and facilitating decision making. The most common ethical challenge was testing prenatally for HD which also results in presymptomatic testing of minors. Participants were divided about how directive to be in response to this ethical issue and about termination of a gene positive pregnancy.

Evaluating the Psychological Effects of Genetic Testing in Symptomatic Patients: A Systematic Review

Most research on the effects of genetic testing is performed in individuals at increased risk for a specific disease (presymptomatic subjects) but not in patients already affected by disease. If results of these studies in presymptomatic subjects can be applied to patients is unclear. We performed a systematic review to evaluate the effects of genetic testing in patients and describe the methodological instruments used. About 2611 articles were retrieved and 16 studies included. Studies reported great variety in designs, methods, and patient outcomes. In total, 2868 participants enrolled of which 62% were patients. Patients appeared to have a lower perceived general health and higher levels of anxiety and depression than presymptomatic subjects before genetic testing. In the long term no psychological impairment was shown. We conclude that patients differ from presymptomatic subjects and may be more vulnerable to negative effects of genetic testing. Conclusions from earlier research on presymptomatic genetic testing cannot be generalized to patients, and more standardized research is needed.