Tay-Sachs disease screening and counseling families at risk for metabolic disease

The incidence and carrier frequency of Tay-Sachs disease in the French-Canadian population of Quebec based on retrospective data from 24 years, 1992-2015

Tay-Sachs disease (TSD) is a hereditary neurodegenerative condition inherited through an autosomal recessive pattern. The incidence and carrier frequency of infantile TSD were found to be increased among French Canadians in specific areas of the province of Quebec or calculated from New England populations with French-Canadian heritage. No accurate infantile TSD carrier frequency for the whole French-Canadian population in Quebec has been published. In this study, we estimate the incidence and carrier frequency of infantile TSD in the Quebec French-Canadian population. The number of TSD cases was ascertained during the 1992-2015 period, as well as the number of births to mothers whose language of use is French. Seven cases of TSD have been diagnosed in Quebec during the period of ascertainment. This corresponds to an incidence of 1/218,144, which in turn corresponds to a carrier frequency of 1/234. In the same 24-year period, there are two French-Canadian couples who had a fetus prenatally diagnosed with TSD. If these cases are included, the incidence of TSD in the French-Canadian population of Quebec is 1/169,668 and the carrier frequency 1/206. These findings can be used for genetic counseling and policy decisions regarding carrier screening for TSD in populations of French-Canadian descent.

THE LYSOSOMAL STORAGE DISEASE GM2 GANGLIOSIDOSIS IN CAPTIVE BANDED MONGOOSE SIBLINGS ( MUNGOS MUNGO)

  This study reports the occurrence of the lysosomal storage disease GM2 gangliosidosis (Sandhoff disease) in two 11-mo-old captive-bred, male and female mongoose siblings ( Mungos mungo). The clinical signs and the pathological findings reported here were similar to those reported in other mammalian species. Light microscopy revealed an accumulation of stored material in neurons and macrophages accompanied by a significant neuronal degeneration (swelling of neuronal soma, loss of Nissl substance, and neuronal loss) and gliosis. Electron microscopy of brain tissue identified the stored material as membrane-bound multilamellar bodies. An almost complete lack of total hexosaminidase activity in serum suggested a defect in the HEXB gene (Sandhoff disease in humans). High-performance thin-layer chromatography and mass spectrometry confirmed the accumulation of GM2 ganglioside in brain and kidney tissue, and the lectin staining pattern of the brain tissue further corroborated the diagnosis of a Sandhoff-type lysosomal storage disease.

Orthodox Jewish Thought Leaders' Insights Regarding BRCA Mutations: A Descriptive Study

PURPOSE

To examine the factors that influence Orthodox Jewish (OJ) thought leaders' perceptions of genetic counseling and testing for BRCA mutations. The specific aims of this study were to describe (1) OJ thought leaders' views on genetic counseling and testing for BRCA mutation status and (2) insights into this high-risk faith-based minority group and their beliefs about counseling and testing for BRCA mutations.

METHODS

In-depth focus groups and demographic questionnaires were used in this descriptive, qualitative study, which was performed in the cancer center of a 750-bed community teaching hospital in Brooklyn, New York. Participants included 17 OJ thought leaders in a large metropolitan area in the northeastern United States.

RESULTS

Four themes emerged that describe the key components of the views of OJ thought leaders regarding genetic counseling and testing for BRCA mutation carriers. There was a high level of concern about cancer, recognition that community norms shift, acknowledgment of the role of the rabbi in medical decision making, and concern about the balance between determinism and personal responsibility in utilizing this health care service.

CONCLUSION

The identification of social contributors to the utilization of genetic counseling and testing, as well as identification of solutions to optimize utilization of BRCA testing, supports the philosophic premise or conceptual model that faith-based leaders are crucial to the promotion of culturally sensitive health care delivery. Incorporating faith-based leaders early in health care strategic planning and implementation can translate into communities better utilizing health-related services.

Ashkenazi Jewish population screening for Tay-Sachs disease: the international and Australian experience

Internationally, Tay-Sachs disease (TSD) preconception screening of Ashkenazi Jewish (AJ) individuals and couples has led to effective primary prevention of TSD. In Australia, adolescent preconception genetic screening programs operate mainly in Jewish community high schools. These existing programs offer an effective means of primary prevention of TSD, are cost effective and safe. However, in the broader Australian community TSD screening is not systematically performed and cases still occur in unscreened AJ individuals. In order to improve the effectiveness of Australian screening, there is a need for definitive guidelines for healthcare professionals to facilitate extension of the proven benefits of preconception TSD screening to all AJ individuals at risk. We performed a systematic review of the relevant literature relating to AJ pre-conception and antenatal screening for TSD. The evidence was assessed using an established National Health and Medical Research Council evidence grading system. Evaluations of efficacy of TSD screening programs design and execution, cost-benefit and cost-utility health economic evaluation, and population outcomes were undertaken. The results have been used to propose a model for universal AJ TSD preconception and antenatal screening for the primary care setting.

Exploring rates of abnormal pharmacogenetic findings in a pain practice

Pharmacogenetic testing (PGT) is part of increasing efforts to personalize medicine, hopefully leading to better medication selection with more effective, less toxic therapies. Pharmacogenetic testing has relevance for chronic pain treatment, given the frequent comorbidities and polypharmacy. This retrospective study explored the prevalence of polymorphisms in a specialty pain practice in Louisiana. Pharmacogenetic testing was conducted for the cytochrome P450 (CYP) enzymes CYP2B6, CYP2C19, and CYP2D6, or the uridine diphosphate-glucuronosyltransferase 2 family polypeptide B15 (UGT2B15) enzyme utilizing a noninvasive, saliva-based test based on clinical decision-making. The sample consisted of 61 men (58.7%) and 41 women (39.4%), with an average age of 46.7 years (range = 23-83, SD = 11.5 years). Across all tests, 164 (42.3%) were extensive, 99 (25.5%) were intermediate, 28 (7.2%) were ultrarapid, and 27 (7%) were poor metabolizers. Only three patients who had been tested were found to be extensive (normal) for all four genes. These data demonstrate that genetic polymorphisms were frequently encountered. Consideration should be given to obtaining PGT as an aspect of evaluation and treatment planning when working with patients in need of specialty pain consultation and care. Caution is needed, as this brief report encompasses results from a single pain practice in one geographic location with a potentially distinct prevalence of genetic polymorphisms. Further prospective study is needed.

GM2 gangliosidosis in a UK study of children with progressive neurodegeneration: 73 cases reviewed

AIM

To report the demographic, phenotypic, and time-to-diagnosis characteristics of children with GM2 gangliosidosis referred to the UK study of Progressive Intellectual and Neurological Deterioration.

METHOD

Case notification is made via monthly surveillance card, administered by the British Paediatric Surveillance Unit to all UK-based paediatricians; children with GM2 gangliosidosis were identified from cases satisfying inclusion in the UK study of Progressive Intellectual and Neurological Deterioration and analysed according to phenotypic and biochemical categories.

RESULTS

Between May 1997 and January 2010, 73 individuals with GM2 gangliosidoses were reported: 40 with Tay-Sachs disease, 31 with Sandhoff disease, and two with GM2 activator protein deficiency. Together they account for 6% (73/1164) of all diagnosed cases of progressive intellectual and neurological deterioration. The majority (62/73) were sporadic index cases with no family history. Children of Pakistani ancestry were overrepresented in all subtypes, particularly juvenile Sandhoff disease, accounting for 10 of 11 notified cases. Infantile-onset variants predominated (55/73); the mean age at onset of symptoms was 6.2 and 4.7 months for infantile-onset Tay-Sachs and Sandhoff disease respectively, and 26.2 and 34.7 months for the corresponding juvenile-onset variants. Time to diagnosis averaged 7.4 months and 28.0 months in infantile- and juvenile-onset disease respectively.

INTERPRETATION

GM2 gangliosidosis is a significant cause of childhood neurodegenerative disease; timely diagnosis relies upon improved clinical recognition, which may be increasingly important as specific therapies become available. There is a potential benefit from the introduction of screening programmes for high-risk ethnic groups.

Prenatal genetic screening and diagnosis for pediatricians

PURPOSE OF REVIEW

Prenatal genetic screening and diagnostic testing can identify many disorders that will require specialized newborn care and follow-up. Pediatricians should be aware of recent advances in testing that may have implications for their patients and families.

RECENT FINDINGS

Over the last half decade, there have been important changes in the breadth and depth of prenatal screening and diagnostic procedures. Carrier screening for selected genetic disorders is now offered routinely to pregnant women or those contemplating pregnancy. Newly developed strategies for first-trimester screening for fetal chromosome abnormalities have improved the detection rate for these disorders, while maintaining a low screen-positive rate. The American College of Obstetricians and Gynecologists and the American College of Medical Genetics now recommend that invasive prenatal diagnostic testing be made available to all pregnant women, regardless of age or prenatal screening results. And prenatal ultrasound findings of unknown clinical significance require that pediatricians provide appropriate follow-up in the newborn period and beyond.

SUMMARY

Prenatal genetic screening and diagnostic tests are changing rapidly, and results of these tests may impact the postnatal evaluation and treatment strategies for pediatric care.

Outcomes of interest in evidence-based evaluations of genetic tests

Genetic tests are increasingly available for use in traditional clinical practice settings and through direct-to-consumer marketing. The need for evidence-based information and guidance on their appropriate use has never been more apparent. The independent Working Group of the Evaluation of Genomic Applications in Practice and Prevention Initiative commissions evidence-based reviews and develops recommendations to inform decision making surrounding the implementation of genetic tests and other applications of genomic technologies into clinical practice. A critical component of this analysis involves the identification and appropriate weighting of relevant health outcomes from genetic testing. Impacts of testing on morbidity and mortality are central considerations although research to document such outcomes can be challenging to conduct. In considering the broader impacts of genetic tests on the individual, familial and societal levels, psychosocial outcomes often take on increasing importance, and their systematic evaluation is a challenge for traditional methods of evidence-based review. Incorporating these types of outcomes in evidence-based processes is possible, however, and necessary to extract balanced and complete (or as complete as available data will allow) information on potential benefits and on potential harms. The framework used by the Evaluation of Genomic Applications in Practice and Prevention Working Group in considering, categorizing, and weighting health-related outcomes as applied to genomic technologies is presented here.

Hexosaminidase assays

beta-Hexosaminidases (EC 3.2.1.52) are lysosomal enzymes that remove terminal beta-glycosidically bound N-acetylglucosamine and N-acetylgalactosamine residues from a number of glycoconjugates. Reliable assay systems are particularly important for the diagnosis of a family of lysosomal storage disorders, the GM2 gangliosidoses that result from inherited beta-hexosaminidase deficiency. More recently, aberrant hexosaminidase levels have also been found to be associated with a variety of inflammatory diseases. Apart from patient testing and carrier screening, practical in vitro assays are indispensable for the characterization of knock-out mice with potentially altered hexosaminidase activities, for detailed structure-function studies aimed at elucidating the enzymatic mechanism, and to characterize newly described enzyme variants from other organisms. The purpose of this article is to discuss convenient hexosaminidase assay procedures for these and other applications, using fluorogenic or chromogenic artificial substrates as well as the physiological glycolipid substrate GM2. Attempts are also made to provide an overview of less commonly used alternative techniques and to introduce recent developments enabling high-throughput screening for enzyme inhibitors.

Newly observed thalamic involvement and mutations of the HEXA gene in a Korean patient with juvenile GM2 gangliosidosis

Neuroimaging studies of patients with GM2 gangliosidosis are rare. The thalamus and basal ganglia are principally involved in patients affected by the infantile form of GM2 gangliosidosis. Unlike in the infantile form, in juvenile or adult type GM2 gangliosidosis, progressive cortical and cerebellar atrophy is the main abnormality seen on conventional magnetic resonance imaging (MRI); no basal ganglial or thalamic impairment were observed. This report is of a Korean girl with subacute onset, severe deficiency of hexosaminidase A activity and mutations (Arg137Term, Ala246Thr) of the HEXA gene. A 3.5-year-old girl who was previously in good health was evaluated for hypotonia and ataxia 3 months ago and showed progressive developmental deterioration, including cognitive decline. Serial brain MRI showed progressive overall volume decrease of the entire brain and thalamic atrophy. Fluorine-18 FDG PET scan showed severe decreased uptake in bilateral thalamus and diffuse cerebral cortex. We suggest, through our experience, that the thalamic involvement in MR imaging and FDG-PET can be observed in the juvenile form of GM2 gangliosidosis, and we suspect the association of mutations in the HEXA gene.

Genetic counselling for familial conditions during pregnancy: a review of the literature published during the years 1989-2004

BACKGROUND

Genetic counselling for familial conditions during pregnancy may have some disadvantages, such as time pressure and induced worry. However, little is known about the reasons for and consequences of this timing of genetic counselling.

OBJECTIVE

The objective of this study was to provide an overview of research aimed at the counselee's reasons for seeking genetic counselling during pregnancy and the medical-technical and procedural consequences thereof.

METHODS

We searched the databases Medline and PsycINFO for primary research papers, reviews and case reports, published from 1989 to June 2004.

RESULTS

No papers could be retrieved which explicitly addressed our research questions. However, 34 papers, out of a total of 399 papers, covered issues with some relevance to our research questions. Limited knowledge and alertness towards genetics and a greater apparent relevance of genetic issues during pregnancy seemed to explain, at least partly, the timing of referral during pregnancy. Literature on the consequences of this timing for the quality of the genetic counselling process appeared to be scarce. These consequences, therefore, remain unclear.

CONCLUSION

In the literature, little attention is paid to the various aspects of the timing of genetic counselling for familial conditions during pregnancy. More research on this issue is important, with a view to improving the care of pregnant women and their children.

From new screens to discovered genes: the successful past and promising present of single gene disorders

Prenatal screening for single gene disorders, which include over 10,000 diverse diseases, presents a great challenge. The major approach to identifying high-risk groups for diseases, from Tay Sachs Disease to sickle cell disease, has historically centered on ethnic-based screening. A major concern in an ethnic-based approach is that carriers belonging to less-traditionally considered populations will be missed. In the United States, the paradigm for a more modern pan-ethnic approach has become exemplified by cystic fibrosis (CF), although considerable debate about future directions remains. CF screening brings several additional issues to the forefront, including that the largest molecular prenatal genetic screening program is based on a single gene disorder that is not necessarily severely disabling. On the other hand, several devastating disorders where screening is indeed available remain relatively inaccessible to prenatal patients in the general population. Future candidates to consider for broad-based screening programs include spinal muscular atrophy (SMA), fragile X, and inborn errors of metabolism. As prenatal screening for single gene disorders expands, issues to consider include inclusion criteria and risk versus benefit.

What's new in prenatal screening and diagnosis?

This article provides clinicians with an overview of current methods for prenatal genetic screening and diagnosis. Topics include developments in prenatal screening procedures such as ethnicity-based carrier testing, maternal serum screening, and ultrasonography. Diagnostic alternatives to amniocentesis include chorionic villus sampling and preimplantation diagnosis. Future endeavors such as three-dimensional ultrasonography and fetal cell sorting are discussed.

Nemaline myopathy in the Ashkenazi Jewish population is caused by a deletion in the nebulin gene

Nemaline myopathy (NM) is a neuromuscular disorder that is clinically diverse and can be attributed to mutations in any of several genes. The Ashkenazi Jewish population, which represents a relatively genetically homogeneous group, has an increased frequency of several genetic disorders and has been the beneficiary of genetic screening programs that have reduced the incidence of these diseases. The identification of individuals with NM in this population has prompted a study of its cause. Our study has revealed that five NM patients from five families bear an identical 2,502-bp deletion that lies in the nebulin gene and that includes exon 55 and parts of introns 54 and 55. The absence of this exon results in the generation of a transcript that encodes 35 fewer amino acids. An analysis of the gene frequency of this mutation in a random sample of 4,090 Ashkenazi Jewish individuals has revealed a carrier frequency of one in 108.