Analysis of intron 22 inversions of the factor VIII gene in severe hemophilia A: implications for genetic counseling

Intrachromosomal recombinations involving F8A, in intron 22 of the factor VIII gene, and one of two homologous regions 500 kb 5' of the factor VIII gene result in large inversions of DNA at the tip of the X chromosome. The gene is disrupted, causing severe hemophilia A. Two inversions are possible, distal and proximal, depending on which homologous region is involved in the recombination event. A simple Southern blotting technique was used to identify patients and carriers of these inversions. In a group of 85 severe hemophilia A patients, 47% had an inversion, of which 80% were of the distal type. There was no association with restriction fragment length polymorphism (RFLP) haplotypes. The technique has identified a definitive genetic marker in families previously uninformative on RFLP analysis and provided valuable information for genetic counselling information may now be provided for carriers without the need to study intervening family members and the diagnosis of severe hemophilia A made in families with only a nonspecific history of bleeding. Analysis of intron 22 inversion should now be the first-line test for carrier diagnosis and genetic counselling for severe hemophilia A and may be particularly useful when there is no affected male family member or when intervening family members are unavailable for testing.     

When is molecular genetic testing for colorectal cancer indicated?

The genetic mutations causing many of the syndromes which confer a high inherited risk of colorectal cancer have now been identified. These include familial adenomatous polyposis, hereditary non-polyposis colorectal cancer, Peutz-Jeghers syndrome, Cowden's syndrome and juvenile polyposis. In all these diseases, the precise mutation is nearly always unique to a particular family; there are few mutation hot spots. This means that mutation detection is technically demanding. Nonetheless, genetic testing can now be used clinically to confirm the diagnosis in affected individuals, and to predict whether an "at risk" family member has inherited the disease and should therefore have endoscopic screening. Because current technology does not detect all mutations, a negative result in a definitely affected individual is diagnostically unhelpful and does not allow predictive testing of other family members. When a mutation can be detected, it is diagnostically very useful, and allows better management of all family members.     

Predictive genetic testing in maturity-onset diabetes of the young (MODY).

INTRODUCTION: Maturity-onset diabetes of the young (MODY) is characterized by autosomal dominant inheritance of young-onset non-insulin-dependent diabetes. It accounts for approximately 1% of Type 2 diabetes (approximately 20 000 people in the UK). Diagnostic and predictive genetic tests are now possible for 80% of MODY families. Diagnostic tests can be helpful as the diagnosis can be confirmed and the subtype defined which has implications for treatment and prognosis. However predictive genetic testing, particularly in children, raises many scientific, ethical and practical questions. METHODS: This is a case report of a family with diabetes resulting from an hepatic nuclear factor (HNF)1alpha mutation, who request a predictive test in their 5-year-old daughter. The scientific issues arising from molecular genetic testing in MODY are discussed, along with the process of genetic counselling. The views of the family and the clinical genetics team involved are presented. RESULTS: The implications of positive and negative predictive test results and the possibility of postponing the test were among many issues discussed during genetic counselling. The family remained convinced the test was appropriate for their daughter and the clinical genetics team fully supported this decision. The family, motivated by their family history of diabetes and personal experiences of the disease, wished to reduce uncertainty about their daughter's future irrespective of the result. CONCLUSIONS: This case emphasizes that decisions on predictive testing are very personal and require appropriate counselling.     

Motion--genetic testing is useful in the diagnosis of nonhereditary pancreatic conditions: arguments for the motion.

Mutations of three major genes are associated with an increased risk of acute and chronic pancreatitis: the cationic trypsinogen (PRSS1) gene, the cystic fibrosis transmembrane conductance regulator (CFTR) gene, and the pancreatic secretory trypsin inhibitor (PSTI) or serine protease inhibitor, Kazal type 1 (SPINK1) gene. Some autosomal dominant forms of hereditary pancreatitis are associated with mutations of the PRSS1 gene, which can be readily identified by genetic testing. Mutations of the CFTR gene can lead either to cystic fibrosis or to idiopathic chronic pancreatitis, and to a variety of cystic fibrosis-associated disorders, including congenital bilateral absence of the vas deferens and sinusitis. These mutations, as with those of the SPINK1 (or PSTI) gene, are prevalent in North America; thus, the presence of such a mutation in an asymptomatic person does not confer a high risk of developing pancreatitis. Combinations of mutations of the PRSS1 and SPINK1 genes lead to more severe disease, as indicated by an earlier onset of symptoms, which suggests that SPINK1 is a disease modifier. The major fear expressed by potential candidates for genetic testing is that the results could lead to insurance discrimination. Studies of the positive predictive value of genetic tests are hampered by recruitment bias and lack of knowledge of family history of pancreatitis. Genetic testing is most useful for persons for whom family members have already been found to exhibit a particular pancreatitis-associated mutation. In the future, increased knowledge of the myriad genetic causes of pancreatitis, as well as advances in the diagnosis and treatment of early chronic pancreatitis, should enhance the utility of genetic testing.     

Role of genetic analyses in cardiology: part I: mendelian diseases: cardiac channelopathies

Genetic analysis can be performed to identify the molecular substrate of inherited arrhythmogenic diseases; however, the role of this information in helping the management of patients is still debated. Here, we support the view that the practical value of genetic analysis is different in the various inherited conditions and that it is strongly influenced by the amount of information available in each disease about genotype-phenotype correlations. In some diseases, clinical management of patients is profoundly affected by the type of the underlying genetic defect; therefore, in these conditions, there is a high priority to introduce genetic analysis into clinical practice. In the absence of genotype-phenotype correlations, genetic testing still can be very useful when there is a clinical advantage in establishing presymptomatic diagnosis or when screening of family members may point to reproductive counseling. Finally, there is a high priority for introducing genetic testing for those genetic diseases in which a limited number of genes allow a high yield of successfully genotyped patients. We have developed a "score" to compare the value of genetic testing in arrhythmogenic diseases and to convey our view that the clinical role of genetic analysis is different in the various inherited cardiomyopathies and channelopathies. Healthcare authorities should become responsive to the advancement of knowledge in this field and should help facilitate access to genotyping for families affected by those conditions in which genetic analysis provides useful information for clinical management.     

Early diagnosis of ATTR amyloidosis through targeted follow-up of identified carriers of TTR gene mutations*

Diagnosis in the early stages of hereditary transthyretin (ATTR) amyloidosis is imperative to support timely treatment to prevent or delay disease progression. Genetic testing in the setting of genetic counselling enables identification of carriers of a TTR gene mutation who are therefore at risk of developing TTR-associated disease. Knowledge of different genotypes and how they manifest in symptomatic disease should facilitate development of a structured and targeted approach to enable diagnosis of symptomatic disease in ATTR amyloidosis mutation carriers on the first manifestation of the earliest detectable sign or symptom. A group of experts from across Europe, Israel and Japan met to reach a consensus on such an approach. The proposed approach involves establishing a baseline for key clinical parameters, determination of the timing and frequency of follow-up in TTR mutation carriers based on a predicted age of disease onset, and recognition of the likely initial clinical signs and symptoms aligned with the phenotype of the specific TTR gene mutation and family history. Minimum criteria for diagnosis of symptomatic disease have been agreed, which it is hoped will ensure diagnosis of ATTR amyloidosis at the earliest possible stage in people with a known TTR mutation.     

Guidelines for genetic testing of inherited cardiac disorders

Inherited gene variants have been implicated increasingly in cardiac disorders but the clinical impact of these discoveries has been variable. For some disorders, such as familial hypertrophic cardiomyopathy, long QT syndrome, and familial hypercholesterolaemia, genetic testing has a high yield and has become an integral part of family management. For other disorders, including dilated cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and atrial fibrillation, relatively less is known about the genes involved and genetic testing has a lower yield. Recent advances in sequencing and array-based technologies promise to change the landscape of our understanding of the genetic basis of human disease and will dramatically increase the rate of detection of genomic variants. Since every individual is expected to harbour thousands of variants, many of which may be novel, interpretation of the functional significance of any single variant is critical, and should be undertaken by experienced personnel. Genotype results can have a wide range of medical and psychosocial implications for affected and unaffected individuals and hence, genetic testing should be performed in a specialised cardiac genetic clinic or clinical genetics service where appropriate family management and genetic counselling can be offered.     

Cardiomyopathies and Genetic Testing in Heart Failure: Role in Defining Phenotype-Targeted Approaches and Management

Cardiomyopathies represent an important cause of heart failure, often affecting young individuals, and have important implications for relatives. Genetic testing for cardiomyopathies is an established care pathway in contemporary cardiology practice. The primary cardiomyopathies where genetic testing is indicated are hypertrophic, dilated, arrhythmogenic, and restrictive cardiomyopathies, with left ventricular noncompaction as a variant phenotype. Early identification and initiation of therapies in patients with inherited cardiomyopathies allow for targeting asymptomatic and presymptomatic patients in stages A and B of the American College of Cardiology/American Heart Association classification of heart failure. The current approach for genetic testing uses gene panel–based testing with the ability to extend to whole-exome and whole-genome sequencing in rare instances. The central components of genetic testing include defining the genetic basis of the diagnosis, providing prognostic information, and the ability to screen and risk-stratify relatives. Genetic testing for cardiomyopathies should be coordinated by a multidisciplinary team including adult and pediatric cardiologists, genetic counsellors, and geneticists, with access to expertise in cardiac imaging and electrophysiology. A pragmatic approach for addressing genetic variants of uncertain significance is important. In this review, we highlight the indications for genetic testing in the various cardiomyopathies, the value of early diagnosis and treatment, family screening, and the care process involved in genetic counselling and testing.     

Genetic counselling in complete androgen insensitivity syndrome: trinucleotide repeat polymorphisms, single-strand conformation polymorphism and direct detection of two novel mutations in the androgen receptor gene

OBJECTIVE Androgen Insensitivity syndrome Is a disorder of male sexual development which results In varying degrees of undervlrlllzatlon In 46XY Individuals with functional testes. In the most severe form, complete androgen insensitivity syndrome (CAIS), patients have a normal female appearance. Although CAIS Is not life-threatening, affected individuals are Infertile and require counselling, gonadectomy, hormone therapy, and sometimes vaginoplasty. Many families therefore request genetic counselling. Defects in the androgen receptor gene account for most if not all cases of CAIS. The purpose of this study was to evaluate the use of the polyglutamlne and polyglycine trinucleotide repeat polymorphisms in the first exon of the androgen receptor gene for carrier status determination In three CAIS families. In two of these families novel mutations In the androgen receptor gene were subsequently identified which allowed confirmation of carrier status and also a prenatal diagnosis to be made in one family. PATIENTS Three CAIS families were studied. The Index cases all presented with a clinical phenotype typical of CAIS. measurements Family members were typed Initially for the polyglutamlne repeat. In one family this was not Informative and the polyglycine repeat was therefore studied. In this and one further family, the androgen receptor gene was sequenced to Identify the mutation causing the CAIS. RESULTS On the basis of Information from trinucleotide repeat analysis carrier status could be assessed In each family. In one family, evidence for somatic instability of the polyglutamlne repeat was found. In the same family, a novel mutation In the androgen receptor gene, which substituted valine for leucine 881, was identified. Other family members were subsequently typed for the mutation and a prenatal diagnosis was performed. A novel mutation was also identified in a second family substituting the glycine codon at position 371 with a stop codon. Other family members were typed for this mutation. CONCLUSIONS Both the polyglutamlne and polyglycine repeat polymorphisms are useful for the genetic counselling of complete androgen Insensitivity syndrome families. In some cases, however, where the family history is limited, more precise information can be provided only once the androgen receptor mutation causing the complete androgen Insensitivity syndrome has been Identified.     

Genetic counseling of hemophilia carriers

Basic analysis of a potential carrier includes calculation of the probability, or odds, for carriership based on pedigree and clotting factor analysis. Genotype assessment constitutes a more accurate method of carrier detection. Where circumstances permit, the genetic diagnosis of hemophilia should be based on the direct identification of the pathogenic mutation in the factor (F) VIII gene. Neutral mutations in the FVIII gene and the risk of mosaicism (a mixture of normal and mutation carrying cells) in sporadic families may cause misclassification. If it is not possible to use the mutation for diagnostic purposes, it may be possible to use linked polymorphic markers (restriction fragment length polymorphisms [RFLP]) to trace the inheritance of the hemophilia gene within a pedigree. Linkage analysis is limited because of uninformative patterns of polymorphic markers, ethnic variation, linkage disequilibrium, and the need for participation of family members, and it is not useful in sporadic families, which constitute more than half of the hemophilia families. Potential carriers of hemophilia should be offered qualified assistance in genetic information, testing, and counseling to help them to cope with the psychological and ethical problems related to carriership of a genetic disorder.     

A newborn with hereditary haemorrhagic telangiectasia and an unusually severe phenotype

Hereditary haemorrhagic telangiectasia (HHT), associated with arteriovenous malformations, is a genetic disease of the vascular system with a frequency of approx. 1:10,000. Genetic diagnosis serves to identify individuals at risk of developing the disease and is a useful tool for genetic counselling purposes. QUESTIONS UNDER STUDY: Here we report on a child presenting severe arteriovenous malformations leading to heart failure. Her mother and grandmother present fewer symptoms of hereditary haemorrhagic telangiectasia. In this study we identify the cause of HHT in the family. METHODS: Clinical examination, PCR, DNA sequencing, quantitative PCR, Southern blot, xray, ultrasound, cardiac catheterisation and angiocardiography. RESULTS: Initially the sequence variant in c.392C>T in the endoglin gene was detected in the grandmother, but not in other affected family members. Further analyses revealed a deletion of exon 1 of endoglin, segregating with the phenotype. CONCLUSIONS: This report points out the need for careful evaluation of molecular genetic findings, particularly in diseases with highly variable phenotype.     

基因诊断一家系3例Wilson病报道

一家系3例以肝病为主要临床表现的患者,经ATP7B基因分析确诊为Wilson病。提示ATP7B基因分析对临床表现不典型的Wilson病患者具有重要的诊疗意义。     

Cystic kidney diseases

Cystic kidney diseases are clinically and genetically heterogeneous. The most important entities are autosomal-dominant and autosomal-recessive polycystic kidney diseases. The proteins encoded by the involved genes are referred to as cystoproteins, which are located predominantly in the primary cilia. Primary cilia play an important role in cyst formation. Inherited polycystic kidney diseases belong to the increasing number of reported ciliopathies, including several syndromic entities. An exact diagnosis is the basis for medical care and genetic counselling; thus, the diagnostic algorithm should include clinical, ultrasonographic and morphological features of the underlying kidney disease, knowledge about further features and family history. Molecular genetic testing may contribute important information towards a definite diagnosis.     

Zystennieren

Cystic kidney diseases are clinically and genetically heterogeneous. The most important entities are autosomal-dominant and autosomal-recessive polycystic kidney diseases. The proteins encoded by the involved genes are referred to as cystoproteins, which are located predominantly in the primary cilia. Primary cilia play an important role in cyst formation. Inherited polycystic kidney diseases belong to the increasing number of reported ciliopathies, including several syndromic entities. An exact diagnosis is the basis for medical care and genetic counselling; thus, the diagnostic algorithm should include clinical, ultrasonographic and morphological features of the underlying kidney disease, knowledge about further features and family history. Molecular genetic testing may contribute important information towards a definite diagnosis.     

Genetic Testing in Inherited Arrhythmias: Approach,Limitations, and Challenges

Genetic testing is playing an ever-expanding role in cardiovascular care and is becoming part of the “toolkit” for the cardiovascular clinician. In patients with inherited arrhythmias, genetic testing can confirm a suspected diagnosis, establish a diagnosis in unexplained cases, and help facilitate cascade family screening. Many inherited arrhythmia syndromes are monogenic diseases arising from a single pathogenic variant involved in the structure and function of cardiac ion channels or structural proteins. As such, “arrhythmia gene panels” will often cast a wide net for such heritable diseases. However, challenges may arise when genetic testing results are ambiguous, or when genetic testing results (genotype) and clinical phenotypes do not match. In cases of “genotype-phenotype matching,” genetic results complement the clinical phenotype and genetic testing can be used in diagnosis, family screening, and occasionally prognostication. It becomes more challenging when genetic results are negative or noncontributory and “contradict” the clinical phenotype. “Genotype mismatches” can also occur when genotype-positive patients have no clinical phenotype, or when genetic testing results point towards a completely different disease than the clinical phenotype. We discuss an approach to genetic testing and review the challenges that may arise when interpreting genetic testing results. Genetic testing has opened a wealth of opportunities in the diagnosis, management, and cascade screening of inherited arrhythmia syndromes, but has also opened a “Pandora’s box” of challenges. Genetic results should be interpreted with caution and in a multidisciplinary clinic, with support from genetic counsellors and an expert with a focused interest in cardiovascular genetics.     

A framework for genetic service provision for haemophilia and other inherited bleeding disorders

This framework document offers guidance to patients, doctors, nurses, laboratory scientists, funders and hospitals on the provision of clinical and laboratory genetic services for haemophilia. With recent advances in molecular laboratory techniques it is now possible to give the vast majority of individual patients and family members very reliable genetic information. To enable these genetic data to be used for both the optimal treatment of patients with inherited bleeding disorders and for appropriate reproductive decisions in carriers, there needs to be a clear and robust framework for systematically acquiring the necessary clinical, personal, family and laboratory information upon which decisions can be made. This document provides guidance on the range and standards of clinical and laboratory genetic services which should be offered to patients and their families. Included are arrangements for genetic counselling and testing (including consent and confidentially issues), management of early pregnancy, standards for laboratory genetic services, as well as advice on data storage, security and retrieval.     

Monogenic diabetes in children and young adults: Challenges for researcher, clinician and patient

Monogenic diabetes results from one or more mutations in a single gene which might hence be rare but has great impact leading to diabetes at a very young age. It has resulted in great challenges for researchers elucidating the aetiology of diabetes and related features in other organ systems, for clinicians specifying a diagnosis that leads to improved genetic counselling, predicting of clinical course and changes in treatment, and for patients to altered treatment that has lead to coming off insulin and injections with no alternative (Glucokinase mutations), insulin injections being replaced by tablets (e.g. low dose in HNFα or high dose in potassium channel defects -Kir6.2 and SUR1) or with tablets in addition to insulin (e.g. metformin in insulin resistant syndromes). Genetic testing requires guidance to test for what gene especially given limited resources. Monogenic diabetes should be considered in any diabetic patient who has features inconsistent with their current diagnosis (unspecified neonatal diabetes, type 1 or type 2 diabetes) and clinical features of a specific subtype of monogenic diabetes (neonatal diabetes, familial diabetes, mild hyperglycaemia, syndromes). Guidance is given by clinical and physiological features in patient and family and the likelihood of the proposed mutation altering clinical care. In this article, I aimed to provide insight in the genes and mutations involved in insulin synthesis, secretion, and resistance, and to provide guidance for genetic testing by showing the clinical and physiological features and tests for each specified diagnosis as well as the opportunities for treatment.     

The future is here: Integrating genetics into the pediatric pulmonary clinic

Recognition of underlying genetic etiologies of disease is increasing at an exponential rate, likely due to greater access to and lower cost of genetic testing. Monogenic causes of disease, or conditions resulting from a mutation or mutations in a single gene, are now well recognized in every subspecialty, including pediatric pulmonary medicine; thus, it is important to consider genetic conditions when evaluating children with respiratory disease. In the pediatric pulmonary clinic, genetic testing should be considered when multiple family members present with similar or related clinical features and when individuals have unusual clinical presentations, such as early‐onset disease or complex, syndromic features. This review provides a practical guide for genetic diagnosis in the pediatric pulmonary setting, including a review of genetic concepts, considerations for test selection and results in interpretation, as well as an overview of genetic differential diagnoses for common pediatric pulmonary phenotypes. Genetic conditions that commonly present to the pediatric pulmonary clinic are reviewed in a companion article by Yonker et al.     

Non-invasive diagnosis and follow-up of hyperferritinaemia

Increased serum ferritin is a very frequent cause of referral for which thorough evaluation is required to avoid unnecessary exploration and inaccurate diagnosis. Clinicians must thus know factors and tools that are relevant in this setting. Several biochemical and radiological tools drastically improved the diagnosis work-up of increased serum ferritin. Because serum ferritin value can be altered by many cofounding factors, scrutiny in the initial clinical evaluation is crucial. Alcohol consumption, and the metabolic syndrome are the most frequent causes of secondary increased ferritin. Serum transferrin saturation level is a pivotal test, and if increased prompt testing for HFE C282Y patients in Caucasian population. In most cases further tests are require to establish whether increased ferritin is associated or not to iron overload. Magnetic resonance imaging is the reference method allowing to accurately establish liver iron content which indirectly reflect body iron load. Second line genetic testing for rare forms of iron overload or increased serum ferritin are available in reference center and should be discussed if diagnosis is equivocal or remain uncertain after careful evaluation. Definite genetic diagnosis is worthwhile as it allows family screening and refining long term management of the patient. Liver biopsy remains seldom useful to assess liver fibrosis, mostly in patients with severe iron overload.     

When should genetic testing be obtained in a patient with phaeochromocytoma or paraganglioma?

About 30% of phaeochromocytoma and paraganglioma patients harbour a germline mutation in one of the known susceptibility genes and in more than one-third of these patients there is no family history for these tumours. The genetic classification, risk assessment and specific management of the patients and at risk family members play an important role in preventive medicine. Distinct diagnostic or therapeutic approaches related to the genetic testing results are and will be even more relevant in the future for the detection of mutation carriers. In addition to a positive family history, other clinical features such as young age at time of manifestation, multifocal tumours and specific tumour location are highly associated with the presence of a germline mutation – genetic testing in these cases should be mandatory. Since several genes are involved in the genetics of phaeochromocytoma and paraganglioma, prioritizing which gene(s) to be tested first by using simple clinical information can reduce the efforts and costs of this analysis. The clinicians offering and performing the genetic testing should provide or make available adequate counselling as well as access to preventive and surveillance options to patients. Collaboration with referral centres and research groups in this field can help to coordinate the management of these patients.