Preimplantation genetic diagnosis

Adults with genetic syndromes and cardiovascular abnormalities: clinical history and management

Cardiovascular abnormalities, especially structural congenital heart defects, commonly occur in malformation syndromes and genetic disorders. Individuals with syndromes comprise a significant proportion of those affected with selected congenital heart defects such as complete atrioventricular canal, interrupted arch type B, supravalvar aortic stenosis, and pulmonary stenosis. As these individuals age, they contribute to the growing population of adults with special health care needs. Although most will require longterm cardiology follow-up, primary care providers, geneticists, and other specialists should be aware of (1) the type and frequency of cardiovascular abnormalities, (2) the range of clinical outcomes, and (3) guidelines for prospective management and treatment of potential complications. This article reviews fundamental genetic, cardiac, medical, and reproductive issues associated with common genetic syndromes that are frequently associated with a cardiovascular abnormality. New data are also provided about the cardiac status of adults with a 22q11.2 deletion and with Down syndrome.

Huntington's disease genetics

Huntington's disease (HD) is a dominantly transmitted neurodegenerative disorder with wide variation in onset age but with an average age at onset of 40 years. Children of HD gene carriers have a 50% chance of inheriting the disease. The characteristic symptoms of HD are involuntary choreiform movements, cognitive impairment, mood disorders, and behavioral changes which are chronic and progressive over the course of the illness. HD is a "trinucleotide repeat" disorder, which is caused by an increase in the number of CAG repeats in the HD gene. Repeats of 40 or larger are associated with disease expression, whereas repeats of 26 and smaller are normal. Intermediate numbers of repeats, between 27 and 35, are not associated with disease expression but may expand in paternal transmission, resulting in the disease in descendents. Repeats of 36-39 are associated with reduced penetrance whereby some develop HD and others do not. The identification of the genetic defect in HD permits direct genetic testing for the presence of the gene alteration responsible for the disease. Tests may be performed in three circumstances: (1) confirmation of diagnosis, (2) predictive testing of persons at genetic risk for inheriting HD, and (3) prenatal testing. Testing is widely available and much experience has been gained with protocols that assist the individual in making an informed choice about test options, and minimize the occurrence of adverse emotional outcomes.

Preimplantation Genetic Diagnosis:

Preimplantation genetic diagnosis (PGD) can provide genetic information on embryos obtained through in vitro fertilization (IVF), allowing implantation of embryos identified as unaffected with a given genetic or chromosomal disorder. With the availability of increasingly sophisticated genetic testing, its use has advanced from the selection of female embryos for the prevention of X-linked genetic diseases to testing for single gene disorders via PCR. Recently, PGD has also been used in the setting of assisted reproductive technology to select for chromosomally normal embryos in an effort to increase the rates of implantation and successful pregnancy. As the number of patients undergoing IVF increases, the indications for its use broadens, and more mutations underlying genetic disorders are identified, PGD is becoming more widespread. As this evolution continues, recognition of the limitations of PGD, as well as ethical concerns regarding use and misuse of this technology, need to be considered by patients, clinicians, and policy makers.

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.

Preimplantation genetic diagnosis of human congenital heart malformation and Holt-Oram syndrome

Holt-Oram syndrome (HOS) is a multiple malformation syndrome associated with congenital heart malformation (CHM) and caused by mutations in the TBX5 transcription factor. Effective prenatal genetic diagnosis of HOS is limited by factors that modify clinical manifestations and confound prediction of an individual's phenotype. Although preimplantation genetic diagnosis (PGD) has been applied to complex disorders with some cardiovascular manifestations, its utility in Mendelian CHM has not been previously demonstrated. We tested whether PGD and in vitro fertilization (IVF) technology, including oocyte donation, can identify fertilized eggs affected by HOS for potential embryo selection. Five donor oocytes were fertilized in vitro with sperm from a HOS patient heterozygous for a Glu69ter-TBX5 mutation and then underwent embryo biopsy and genotyping. One carried the Glu69ter-TBX5 mutation; all others had wildtype genotypes. Two wildtype blastocysts were transferred to the mother, and the resulting singleton pregnancy was successfully delivered. Mutational analysis of fetal amniocytes and postpartum umbilical cord blood confirmed PGD. Fetal ultrasonography as well as postpartum electrocardiography and echocardiography also validated accurate prediction of normal skeletal and cardiac phenotypes. We conclude that PGD is an effective reproductive strategy for HOS patients. As more genetic etiologies for CHM are identified, application of PGD as adjunctive therapy to IVF will be increasingly available to prevent transmission of such diseases from affected parents to their children. Clinical application of PGD must balance the benefits of avoiding disease transmission with the medical risks and financial burdens of IVF.