The Expansion of Genetic Testing in Cardiovascular Medicine: Preparing the Cardiology Community for the Changing Landscape.

PURPOSE OF REVIEW: Pathogenic DNA variants underlie many cardiovascular disease phenotypes. The most well-recognized of these include familial dyslipidemias, cardiomyopathies, arrhythmias, and aortopathies. The clinical presentations of monogenic forms of cardiovascular disease are often indistinguishable from those with complex genetic and non-genetic etiologies, making genetic testing an essential aid to precision diagnosis. RECENT FINDINGS: Precision diagnosis enables efficient management, appropriate use of emerging targeted therapies, and follow-up of at-risk family members. Genetic testing for these conditions is widely available but under-utilized. In this review, we summarize the potential benefits of genetic testing, highlighting the specific cardiovascular disease phenotypes in which genetic testing should be considered, and how clinicians can integrate guideline-directed genetic testing into their practice.

DNA sequence analysis and genotype-phenotype assessment in 71 patients with syndromic hearing loss or auditory neuropathy.

OBJECTIVES: Aetiological assessment of 71 probands whose clinical presentation suggested a genetic syndrome or auditory neuropathy. METHODS: Sanger sequencing was performed on DNA isolated from peripheral blood or lymphoblastoid cell lines. Genes were selected for sequencing based on each patient's clinical presentation and suspected diagnosis. Observed DNA sequence variations were assessed for pathogenicity by review of the scientific literature, and mutation and polymorphism databases, through the use of in silico tools including sorting intolerant from tolerant (SIFT) and polymorphism phenotyping (PolyPhen), and according to the recommendations of the American College of Medical Genetics and Genomics for the interpretation of DNA sequence variations. Novel DNA sequence variations were sought in controls. RESULTS: DNA sequencing of the coding and near-coding regions of genes relevant to each patient's clinical presentation revealed 37 sequence variations of known or uncertain pathogenicity in 9 genes from 25 patients. 14 novel sequence variations were discovered. Assessment of phenotypes revealed notable findings in 9 patients. CONCLUSIONS: DNA sequencing in patients whose clinical presentation suggested a genetic syndrome or auditory neuropathy provided opportunities for aetiological assessment and more precise genetic counselling of patients and families. The failure to identify a genetic aetiology in many patients in this study highlights the extreme heterogeneity of genetic hearing loss, the incompleteness of current knowledge of aetiologies of hearing loss, and the limitations of conventional DNA sequencing strategies that evaluate only coding and near-coding segments of genes.

American College of Medical Genetics and Genomics guideline for the clinical evaluation and etiologic diagnosis of hearing loss.

Hearing loss is a common and complex condition that can occur at any age, can be inherited or acquired, and is associated with a remarkably wide array of etiologies. The diverse causes of hearing loss, combined with the highly variable and often overlapping presentations of different forms of hearing loss, challenge the ability of traditional clinical evaluations to arrive at an etiologic diagnosis for many deaf and hard-of-hearing individuals. However, identifying the etiology of a hearing loss may affect clinical management, improve prognostic accuracy, and refine genetic counseling and assessment of the likelihood of recurrence for relatives of deaf and hard-of-hearing individuals. Linguistic and cultural identities associated with being deaf or hard of hearing can complicate access to and the effectiveness of clinical care. These concerns can be minimized when genetic and other health-care services are provided in a linguistically and culturally sensitive manner. This guideline offers information about the frequency, causes, and presentations of hearing loss and suggests approaches to the clinical evaluation of deaf and hard-of-hearing individuals aimed at identifying an etiologic diagnosis and providing informative and effective patient education and genetic counseling.

Enhancing exposure to genetics and genomics through an innovative medical school curriculum.

PURPOSE: Physicians entering medical practice in the 21st century will require more than a basic understanding of human genetics because of rapid progress in the field of genetics and genomics. The current undergraduate medical curriculum at most institutions is not adequate to prepare medical students for these challenges. Enhancing exposure to genetics throughout the medical school curriculum should help prepare the next generation of physicians to use genetic and genomic information for optimal patient care. METHODS: We have introduced a Genetics Track Curriculum to the undergraduate medical curriculum at Baylor College of Medicine. RESULTS: This track runs in parallel to the existing 4-year curriculum and includes didactic sessions, small group discussions, longitudinal clinical experiences, clinical and laboratory rotations, community outreach, and scholarly projects related to genetics. It also provides the students a means to network and discuss topics and career paths in medical genetics. CONCLUSION: We have developed a novel curriculum that enhances genomic education for medical students with the ultimate goal of enabling our graduates to deliver more effective and personalized medical care. We believe that the Genetics Track Curriculum at Baylor College of Medicine can serve as a prototype for other medical schools across the country and abroad.

Basic medical genetics for the otolaryngologist.

Medical genetics is becoming an increasingly important part of the practice of medicine across every medical specialty. For otolaryngologists, understanding the genetic basis of hearing loss, tumors of the head and neck and other otolaryngologic conditions is crucial to effectively incorporating medical genetics information, tools and services into patient care. A clinician who understands the genetic basis of disease, mechanisms of genetic mutation and patterns of inheritance will be positioned to diagnose genetic conditions, interpret genetic test results, assess genetic risks for relatives of patients and refer patients and families for medical genetics and other specialty care. The family medical history is an indispensible tool that, when used properly, can aid in the recognition of genetic susceptibilities within a family and offer opportunities for early intervention. However, obtaining a family medical history is not as simple as it might seem. Knowing what questions to ask, how to properly draw a pedigree and how to recognize patterns of inheritance are critical to obtaining an informative family medical history and using the information in a clinical setting. This article provides a brief introduction to basic medical genetics that includes descriptions of the human genome, the genetic basis of human disease and patterns of inheritance, and a primer for collecting family medical history information.

Nonsyndromic hereditary hearing loss.

The etiology of hereditary hearing loss is extraordinarily complex. More than 400 genetic syndromes are associated with hearing loss and more than 140 genetic loci associated with nonsyndromic hearing loss have been mapped, with more than 60 genes identified to date. Hereditary hearing loss can be inherited as an autosomal dominant, autosomal recessive, X-linked or mitochondrial (maternally inherited) condition. The overlapping audiologic phenotypes associated with many genes and the variability and/or reduced, sometimes age-related, penetrance of some phenotypic features of syndromic hearing loss can complicate the distinction between various genetic causes of nonsyndromic hearing loss and between nonsyndromic and syndromic hearing loss, especially in childhood. Testing for individual genes associated with nonsyndromic hearing loss, beyond GJB2 which encodes Connexin 26, can become expensive and, without specific phenotypic features to guide selection of genes for testing (such as enlarged vestibular aqueducts, low frequency hearing loss or auditory neuropathy), it is not likely to yield an etiology. Advances in DNA sequencing and the rapid decline in the cost of sequencing presage the availability of testing that can identify the etiology in the majority of cases of genetic hearing loss. However, until comprehensive genetic testing of hearing loss is clinically available and cost-effective, thorough phenotypic and audiologic evaluation and careful documentation of risk factors, infectious exposures and patient and family medical history will continue to be important to efforts directed toward etiologic diagnosis. The complexities associated with interpretation of genetic test results, genetic counseling and genetic risk assessment make consultation with medical geneticists important for many patients.

High frequency of the IVS2-2A>G DNA sequence variation in SLC26A5, encoding the cochlear motor protein prestin, precludes its involvement in hereditary hearing loss.

BACKGROUND: Cochlear outer hair cells change their length in response to variations in membrane potential. This capability, called electromotility, is believed to enable the sensitivity and frequency selectivity of the mammalian cochlea. Prestin is a transmembrane protein required for electromotility. Homozygous prestin knockout mice are profoundly hearing impaired. In humans, a single nucleotide change in SLC26A5, encoding prestin, has been reported in association with hearing loss. This DNA sequence variation, IVS2-2A>G, occurs in the exon 3 splice acceptor site and is expected to abolish splicing of exon 3. METHODS: To further explore the relationship between hearing loss and the IVS2-2A>G transition, and assess allele frequency, genomic DNA from hearing impaired and control subjects was analyzed by DNA sequencing. SLC26A5 genomic DNA sequences from human, chimp, rat, mouse, zebrafish and fruit fly were aligned and compared for evolutionary conservation of the exon 3 splice acceptor site. Alternative splice acceptor sites within intron 2 of human SLC26A5 were sought using a splice site prediction program from the Berkeley Drosophila Genome Project. RESULTS: The IVS2-2A>G variant was found in a heterozygous state in 4 of 74 hearing impaired subjects of Hispanic, Caucasian or uncertain ethnicity and 4 of 150 Hispanic or Caucasian controls (p = 0.45). The IVS2-2A>G variant was not found in 106 subjects of Asian or African American descent. No homozygous subjects were identified (n = 330). Sequence alignment of SLC26A5 orthologs demonstrated that the A nucleotide at position IVS2-2 is invariant among several eukaryotic species. Sequence analysis also revealed five potential alternative splice acceptor sites in intron 2 of human SLC26A5. CONCLUSION: These data suggest that the IVS2-2A>G variant may not occur more frequently in hearing impaired subjects than in controls. The identification of five potential alternative splice acceptor sites in intron 2 of human SLC26A5 suggests a potential mechanism by which expression of prestin might be maintained in cells carrying the SLC26A5 IVS2-2A>G DNA sequence variation. Additional studies are needed to evaluate the effect of the IVS2-2A>G transition on splicing of SLC26A5 transcripts and characterize the hearing status of individuals homozygous for the IVS2-2A>G variant.

Quantitative analysis of herpes simplex virus in cranial nerve ganglia.

A susceptible individual exposed to herpes simplex virus (HSV) will develop latent infection in multiple cranial nerve ganglia. There are a few quantitative studies of the viral load within the trigeminal ganglion, but none that investigate other cranial nerve ganglia. In this study, human trigeminal, geniculate, vestibular (Scarpa's) and cochlear (spiral) ganglia were obtained from willed body donors. Real time quantitative polymerase chain reaction (PCR) analysis of the HSV DNA polymerase gene was performed on ipsilateral ganglion sets from the same individual. Viral load, expressed as HSV genomes per 105 cells, was significantly greater in the vestibular ganglion (mean +/- SD, 176705 +/- 255916) than in the geniculate (9948 +/- 22066), cochlear (3527 +/- 9360), or trigeminal (2017 +/- 5578) ganglia. There was not a significant correlation among ganglia from the same individual. The results support the hypothesis that neuronal subpopulations have variable susceptibility to HSV infection.

Early childhood hearing loss: clinical and molecular genetics. An educational slide set of the American College of Medical Genetics.

An educational slide set entitled "Early Childhood Hearing Loss: Clinical and Molecular Genetics" is offered by the American College of Medical Genetics (ACMG). The slide set is produced in Microsoft PowerPoint 2002. It is extensively illustrated and supported with teaching tools, explanations of each slide and figure, links to Internet resources, and a bibliography. The slide set is expected to be used as a resource for self-directed learning and in support of medical genetics teaching activities. The slide set is available through the ACMG (http://www.acmg.net) for $20, plus applicable tax and shipping. It is the first in a series of educational slide sets to be developed by the ACMG.