Variant interpretation is a component of clinical practice among genetic counselors in multiple specialties.

PURPOSE: Genomic testing is routinely utilized across clinical settings and can have significant variant interpretation challenges. The extent of genetic counselor (GC) engagement in variant interpretation in clinical practice is unknown. This study aimed to explore clinical GCs' variant interpretation practice across specialties, understand outcomes of this practice, and identify resource and educational needs. METHODS: An online survey was administered to National Society of Genetic Counselors members providing clinical counseling. RESULTS: Respondents (n = 239) represented all major clinical specialties. The majority (68%) reported reviewing evidence documented by the laboratory for most (>60%) variants reported; 45.5% report seeking additional evidence. Prenatal GCs were less likely to independently assess reported evidence. Most respondents (67%) report having reached a different conclusion about a variant's classification than the testing laboratory, though infrequently. Time was the most commonly reported barrier (72%) to performing variant interpretation, though the majority (97%) indicated that this practice had an important impact on patient care. When presented with three hypothetical scenarios, evidence typically used for variant interpretation was generally applied correctly. CONCLUSION: This study is the first to document variant interpretation practice broadly across clinical GC specialties. Our results suggest that variant interpretation should be considered a practice-based competency for GCs.

Correction: Adapting ACMG/AMP sequence variant classification guidelines for single-gene copy-number variants.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Targeted exome analysis identifies the genetic basis of disease in over 50% of patients with a wide range of ataxia-related phenotypes.

PURPOSE: To examine the impact of a targeted exome approach for the molecular diagnosis of patients nationwide with a wide range of ataxia-related phenotypes. METHODS: One hundred and seventy patients with ataxia of unknown etiology referred from clinics throughout the United States and Canada were studied using a targeted exome approach. Patients ranged in age from 2 to 88 years. Analysis was focused on 441 curated genes associated with ataxia and ataxia-like conditions. RESULTS: Pathogenic and suspected diagnostic variants were identified in 88 of the 170 patients, providing a positive molecular diagnostic rate of 52%. Forty-six different genes were implicated, with the six most commonly mutated genes being SPG7, SYNE1, ADCK3, CACNA1A, ATP1A3, and SPTBN2, which accounted for >40% of the positive cases. In many cases a diagnosis was provided for conditions that were not suspected and resulted in the broadening of the clinical spectrum of several conditions. CONCLUSION: Exome sequencing with targeted analysis provides a high-yield approach for the genetic diagnosis of ataxia-related conditions. This is the largest targeted exome study performed to date in patients with ataxia and ataxia-like conditions and represents patients with a wide range of ataxia phenotypes typically encountered in neurology and genetics clinics.

A novel mutation in the promoter of RARS2 causes pontocerebellar hypoplasia in two siblings.

Pontocerebellar hypoplasia (PCH) is characterized by hypoplasia and atrophy of the cerebellum, variable pontine atrophy, microcephaly, severe mental and motor impairments and seizures. Mutations in 11 genes have been reported in 8 out of 10 forms of PCH. Recessive mutations in the mitochondrial arginyl-transfer RNA synthetase gene (RARS2) have been recently associated with PCH type 6, which is characterized by early-onset encephalopathy with signs of oxidative phosphorylation defect. Here we describe the clinical presentation, neuroimaging findings and molecular characterizations of two siblings with a clinical diagnosis of PCH who displayed a novel variant (c.-2A>G) in the 5'-UTR of the RARS2 gene in the homozygous state. This variant was identified through next-generation sequencing testing of a panel of nine genes known to be involved in PCH. Gene expression and functional studies demonstrated that the c.-2A>G sequence change directly leads to a reduced RARS2 messenger RNA expression in the patients by decreasing RARS2 promoter activity, thus providing evidence that mutations in the RARS2 promoter are likely to represent a new causal mechanism of PCH6.

Reinitiation of mRNA translation in a patient with X-linked infantile spasms with a protein-truncating variant in ARX.

Mutations in the Aristaless-related homeobox gene (ARX) lead to a range of X-linked intellectual disability phenotypes, with truncating variants generally resulting in severe X-linked lissencephaly with ambiguous genitalia (XLAG), and polyalanine expansions and missense variants resulting in infantile spasms. We report two male patients with early-onset infantile spasms in whom a novel c.34G>T (p.(E12*)) variant was identified in the ARX gene. A similar variant c.81C>G (p.(Y27*)), has previously been described in two affected cousins with early-onset infantile spasms, leading to reinitiation of ARX mRNA translation resulting in an N-terminal truncated protein. We show that the novel c.34G>T (p.(E12*)) variant also reinitiated mRNA translation at the next AUG codon (c.121-123 (p.M41)), producing the same N-terminally truncated protein. The production of both of these truncated proteins was demonstrated to be at markedly reduced levels using in vitro cell assays. Using luciferase reporter assays, we demonstrate that transcriptional repression capacity of ARX was diminished by both the loss of the N-terminal corepressor octapeptide domain, as a consequence of truncation, and the marked reduction in mutant protein expression. Our study indicates that premature termination mutations very early in ARX lead to reinitiation of translation to produce N-terminally truncated protein at markedly reduced levels of expression. We conclude that even low levels of N-terminally truncated ARX is sufficient to improve the patient's phenotype compared with the severe phenotype of XLAG that includes malformations of the brain and genitalia normally seen in complete loss-of-function mutations in ARX.

Evaluation of laboratory perspectives on hereditary cancer panels.

Genetic counseling and testing for hereditary cancer susceptibility is a rapidly evolving field and partly a result of next-generation sequencing (NGS) allowing analysis of multiple cancer susceptibility genes simultaneously. This qualitative study explored laboratory perspectives on hereditary cancer panels. Semi-structured interviews were conducted with representatives of clinical laboratories offering hereditary cancer panels via NGS. Several themes emerged from the responses pertaining to hereditary cancer panel development, the importance of communication of panel properties with patients, variant reporting policies, and the future of hereditary cancer gene testing. Clinical utility was discussed as primary consideration during panel development. In addition, while participants indicated gene and syndrome overlap prompted panel development in general, laboratories differed in their opinions of whether phenotypic overlap warrants offering pan-cancer panels only versus cancer specific panels. Participants stressed the importance of patients understanding implications of panel testing, including what is tested for and limitations of testing. While all laboratories discussed the limitations of a variant of uncertain significance result, they differed significantly in their reporting methods. This study provides healthcare providers information on the laboratory approach to panel testing, highlighting both commonalities and differences in laboratory approaches, and may allow providers to make more informed decisions when ordering hereditary cancer panels.

Improved molecular diagnosis of patients with neonatal diabetes using a combined next-generation sequencing and MS-MLPA approach.

BACKGROUND: We evaluated a methylation-specific multiplex-ligation-dependent probe amplification (MS-MLPA) assay for the molecular diagnosis of transient neonatal diabetes mellitus (TNDM) caused by 6q24 abnormalities and assessed the clinical utility of using this assay in combination with next generation sequencing (NGS) analysis for diagnosing patients with neonatal diabetes (NDM). METHODS: We performed MS-MLPA in 18 control samples and 42 retrospective NDM cases with normal bi-parental inheritance of chromosome 6. Next, we evaluated 22 prospective patients by combining NGS analysis of 11 NDM genes and the MS-MLPA assay. RESULTS: 6q24 aberrations were identified in all controls and in 19% of patients with normal bi-parental inheritance of chromosome 6. The MS-MLPA/NGS combined approach identified a genetic cause in ~64% of patients with NDM of unknown etiology. CONCLUSIONS: MS-MLPA is a reliable method to identify all known 6q24 abnormalities and comprehensive testing of all causes reveals a causal mutation in ~64% of patients.

Clinical utility of next-generation sequencing for the molecular diagnosis of monogenic diabetes.

Monogenic diabetes resulting from mutations that primarily reduce insulin-secreting pancreatic ß-cell function accounts for 1-2% of all cases of diabetes, and is genetically and clinically heterogeneous. Currently, genetic testing for monogenic diabetes relies on selection of the appropriate gene for analysis based on the availability of comprehensive phenotypic information, which can be time consuming, costly and can limit the differential diagnosis to a few selected genes. In recent years, the exponential growth in the field of high-throughput capture and sequencing technology has made it possible and cost effective to sequence many genes simultaneously, making it an efficient diagnostic tool for clinically and genetically heterogeneous disorders such as monogenic diabetes. Making a diagnosis of monogenic diabetes is important as it enables more appropriate treatment, better prediction of disease prognosis and progression, and counseling and screening of family members. We provide a concise overview of the genetic etiology of some forms of monogenic diabetes, as well as a discussion of the clinical utility of genetic testing by comprehensive multigene panel using next-generation sequencing methodologies.