Huntington's disease (HD) is caused by an expanded N-terminal glutamine tract that endows huntingtin with a striatal-selective structural property ultimately toxic to medium spiny neurons. In precise genetic models of juvenile HD, HdhQ92 and HdhQ111 knock-in mice, long polyglutamine segments change huntingtin's physical properties, producing HD-like in vivo correlates in the striatum, including nuclear localization of a version of the full-length protein predominant in medium spiny neurons, and subsequent formation of N-terminal inclusions and insoluble aggregate. These changes show glutamine length dependence and dominant inheritance with recruitment of wild-type protein, critical features of the altered HD property that strongly implicate them in the HD disease process and that suggest alternative pathogenic scenarios: the effect of the glutamine tract may act by altering interaction with a critical cellular constituent or by depleting a form of huntingtin essential to medium spiny striatal neurons.

The CAG repeats in the human Huntington's disease (HD) gene exhibit striking length-dependent intergenerational instability, typically small size increases or decreases of one to a few CAGs, but little variation in somatic tissues. In a subset of male transmissions, larger size increases occur to produce extreme HD alleles that display somatic instability and cause juvenile onset of the disorder. Initial efforts to reproduce these features in a mouse model transgenic for HD exon 1 with 48 CAG repeats revealed only mild intergenerational instability ( approximately 2% of meioses). A similar pattern was obtained when this repeat was inserted into exon 1 of the mouse Hdh gene. However, lengthening the repeats in Hdh to 90 and 109 units produced a graded increase in the mutation frequency to >70%, with instability being more evident in female transmissions. No large jumps in CAG length were detected in either male or female transmissions. Instead, size changes were modest increases and decreases, with expansions typically emanating from males and contractions from females. Limited CAG variation in the somatic tissues gave way to marked mosaicism in liver and striatum for the longest repeats in older mice. These results indicate that gametogenesis is the primary source of inherited instability in the Hdh knock-in mouse, as it is in man, but that the underlying repeat length-dependent mechanism, which may or may not be related in the two species, operates at higher CAG numbers. Moreover, the large CAG repeat increases seen in a subset of male HD transmissions are not reproduced in the mouse, suggesting that these arise by a different fundamental mechanism than the small size fluctuations that are frequent during gametogenesis in both species.

Genome-scale sequencing creates vast amounts of genomic data, increasing the challenge of clinical sequence variant interpretation. The demand for high-quality interpretation requires multiple specialties to join forces to accelerate the interpretation of sequence variant pathogenicity. With over 600 international members including clinicians, researchers, and laboratory diagnosticians, the Clinical Genome Resource (ClinGen), funded by the National Institutes of Health (NIH), is forming expert groups to systematically evaluate variants in clinically relevant genes. Here, we describe the first ClinGen Variant Curation Expert Panels (VCEPs), development of consistent and streamlined processes for establishing new VCEPs, and creation of standard operating procedures (SOPs) for VCEPs to define application of the ACMG/AMP guidelines for sequence variant interpretation in specific genes or diseases. Additionally, ClinGen has created user interfaces to enhance reliability of curation and a Sequence Variant Interpretation Working Group (SVI WG) to harmonize guideline specifications and ensure consistency between groups. The expansion of VCEPs represents the primary mechanism by which curation of a substantial fraction of genomic variants can be accelerated and ultimately undertaken systematically and comprehensively. We welcome groups to utilize our resources and become involved in our effort to create a publicly accessible, centralized resource for clinically relevant genes and variants.

The growth of patents that include genetic sequences has been accompanied by concern about their impact on the ability of physicians to provide clinical genetic testing services and to perform research. Therefore, we conducted a survey of clinical laboratory directors that perform DNA-based genetic tests to examine potential effects. We performed a telephone survey between July and September in 2001 of all laboratory directors in the United States who were members of the Association for Molecular Pathology or who were listed on the GeneTests.org website. One hundred thirty-two of 211 (63%) laboratory directors were interviewed. Ten of these were excluded because they did not conduct DNA-based genetic tests. Almost all performed genetic tests for clinical purposes. Half performed tests for research purposes as well. Twenty-five percent of respondents reported that they had stopped performing a clinical genetic test because of a patent or license. Fifty-three percent of respondents reported deciding not to develop a new clinical genetic test because of a patent or license. In total, respondents were prevented from performing 12 genetic tests, and all of these tests were among those performed by a large number of laboratories. We found 22 patents that were relevant to the performance of these 12 tests. Fifteen of the 22 patents (68%) are held by universities or research institutes, and 13 of the 22 patents (59%) were based on research funded by the United States Government. Overall, respondents reported that their perceptions of the effects of patents on the cost, access, and development of genetic tests, or data sharing among researchers, were negative. In contrast, most respondents felt that patents did not have an effect on the quality of testing. We conclude that patents and li- Patents were created to provide incentives for the production of innovative products that could benefit the public. It is argued that patents have been critical to the growth and maintenance of the pharmaceutical industry.

PurposeGenome and exome sequencing can identify variants unrelated to the primary goal of sequencing. Detecting pathogenic variants associated with an increased risk of a medical disorder allows the possibility of clinical interventions to improve future health outcomes in patients and their at-risk relatives. The Clinical Genome Resource, or ClinGen, aims to assess clinical actionability of genes and associated disorders as part of a larger effort to build a central resource on the clinical relevance of genomic variation for use in precision medicine and research.MethodsWe developed a practical, standardized protocol to identify available evidence and generate qualitative summary reports of actionability for disorders and associated genes. We applied a semi-quantitative metric to score actionability.ResultsWe generated summary reports and actionability scores for the 56 genes and associated disorders recommended by the American College of Medical Genetics and Genomics for return as secondary findings from clinical genome-scale sequencing. We also describe the challenges that arose during the development of the protocol which highlight important issues in characterizing actionability across a range of disorders.ConclusionThe ClinGen framework for actionability assessment will assist research and clinical communities in making clear, efficient, and consistent determinations of actionability based on transparent criteria to guide analysis and reporting of findings from clinical genome-scale sequencing.