Myotonic dystrophy type 1 testing, 2024 revision: A technical standard of the American College of Medical Genetics and Genomics (ACMG).

Myotonic dystrophy type 1 (DM1) is a form of muscular dystrophy causing progressive muscle loss and weakness. Although clinical features can manifest at any age, it is the most common form of muscular dystrophy with onset in adulthood. DM1 is an autosomal dominant condition, resulting from an unstable CTG expansion in the 3'-untranslated region of the myotonic dystrophy protein kinase (DMPK) gene. The age of onset and the severity of the phenotype are roughly correlated with the size of the CTG expansion. Multiple methodologies can be used to diagnose affected individuals with DM1, including polymerase chain reaction, Southern blot, and triplet repeat-primed polymerase chain reaction. Recently, triplet repeat interruptions have been described, which may affect clinical outcomes of a fully-variable allele in DMPK. This document supersedes the Technical Standards and Guidelines for Myotonic Dystrophy originally published in 2009 and reaffirmed in 2015. It is designed for genetic testing professionals who are already familiar with the disease and the methods of analysis.

Next-Generation Sequencing Somatic and Germline Assay Troubleshooting Guide Derived From Proficiency Testing Data.

CONTEXT.­: Next-generation sequencing-based assays are increasingly used in clinical molecular laboratories to detect somatic variants in solid tumors and hematologic malignancies and to detect constitutional variants. Proficiency testing data are potential sources of information about challenges in performing these assays. OBJECTIVE.­: To examine the most common sources of unacceptable results from the College of American Pathologists Next-Generation Sequencing Bioinformatics, Hematological Malignancies, Solid Tumor, and Germline surveys and provide recommendations on how to avoid these pitfalls and improve performance. DESIGN.­: The College of American Pathologists next-generation sequencing somatic and germline proficiency testing survey results from 2016 to 2019 were analyzed to identify the most common causes of unacceptable results. RESULTS.­: On somatic and germline proficiency testing surveys, 95.9% (18 815/19 623) and 97.8% (33 890/34 641) of all variants were correctly identified, respectively. The most common causes of unacceptable results related to sequencing were false-negative errors in genomic regions that were difficult to sequence because of high GC content. False-positive errors occurred in the context of homopolymers and pseudogenes. Recurrent errors in variant annotation were seen for dinucleotide and duplication variants and included unacceptable transcript selection and outdated variant nomenclature. A small percentage of preanalytic or postanalytic errors were attributed to specimen swaps and transcription errors. CONCLUSIONS.­: Laboratories demonstrate overall excellent performance for detecting variants in both somatic and germline proficiency testing surveys. Proficiency testing survey results highlight infrequent, but recurrent, analytic and nonanalytic challenges in performing next- generation sequencing-based assays and point to remedies to help laboratories improve performance.

Next-generation sequencing for constitutional variants in the clinical laboratory, 2021 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG).

Next-generation sequencing (NGS) technologies are now established in clinical laboratories as a primary testing modality in genomic medicine. These technologies have reduced the cost of large-scale sequencing by several orders of magnitude. It is now cost-effective to analyze an individual with disease-targeted gene panels, exome sequencing, or genome sequencing to assist in the diagnosis of a wide array of clinical scenarios. While clinical validation and use of NGS in many settings is established, there are continuing challenges as technologies and the associated informatics evolve. To assist clinical laboratories with the validation of NGS methods and platforms, the ongoing monitoring of NGS testing to ensure quality results, and the interpretation and reporting of variants found using these technologies, the American College of Medical Genetics and Genomics (ACMG) has developed the following technical standards.

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

PURPOSE: The ability of a single technology, next-generation sequencing, to provide both sequence and copy number variant (CNV) results has driven the merger of clinical cytogenetics and molecular genetics. Consequently, the distinction between the definition of a sequence variant and a CNV is blurry. As the 2015 American College of Medical Genetics and Genomics/Association for Molecular Pathology (ACMG/AMP) standards and guidelines for interpretation of sequence variants address CNV classification only sparingly, this study focused on adapting ACMG/AMP criteria for single-gene CNV interpretation. METHODS: CNV-specific modifications of the 2015 ACMG/AMP criteria were developed and their utility was independently tested by three diagnostic laboratories. Each laboratory team interpreted the same 12 single-gene CNVs using three systems: (1) without ACMG/AMP guidance, (2) with ACMG/AMP criteria, and (3) with new modifications. A replication study of 12 different CNVs validated the modified criteria. RESULTS: The adapted criteria system presented here showed improved concordance and usability for single-gene CNVs compared with using the ACMG/AMP interpretation guidelines focused on sequence variants. CONCLUSION: These single-gene CNV criteria modifications could be used as a supplement to the ACMG/AMP guidelines for sequence variants, allowing for a streamlined workflow and a step toward a uniform classification system for both sequence and copy number alterations.

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.

Diagnostic gene sequencing panels: from design to report-a technical standard of the American College of Medical Genetics and Genomics (ACMG).

Gene sequencing panels are a powerful diagnostic tool for many clinical presentations associated with genetic disorders. Advances in DNA sequencing technology have made gene panels more economical, flexible, and efficient. Because the genes included on gene panels vary widely between laboratories in gene content (e.g., number, reason for inclusion, evidence level for gene-disease association) and technical completeness (e.g., depth of coverage), standards that address technical and clinical aspects of gene panels are needed. This document serves as a technical standard for laboratories designing, offering, and reporting gene panel testing. Although these principles can apply to multiple indications for genetic testing, the primary focus is on diagnostic gene panels (as opposed to carrier screening or predictive testing) with emphasis on technical considerations for the specific genes being tested. This technical standard specifically addresses the impact of gene panel content on clinical sensitivity, specificity, and validity-in the context of gene evidence for contribution to and strength of evidence for gene-disease association-as well as technical considerations such as sequencing limitations, presence of pseudogenes/gene families, mosaicism, transcript choice, detection of copy-number variants, reporting, and disclosure of assay limitations.

The first pediatric case of glucagon receptor defect due to biallelic mutations in GCGR is identified by newborn screening of elevated arginine.

Glucagon receptor (GCGR) defect (Mahvash disease) is an autosomal recessive hereditary pancreatic neuroendocrine tumor (PNET) syndrome that has only been reported in adults with pancreatic α cell hyperplasia and PNETs. We describe a 7-year-old girl with persistent hyperaminoacidemia, notable for elevations of glutamine (normal ammonia), alanine (normal lactate), dibasic amino acids (arginine, lysine and ornithine), threonine and serine. She initially was brought to medical attention by an elevated arginine on newborn screening (NBS) and treated for presumed arginase deficiency with a low protein diet, essential amino acids formula and an ammonia scavenger drug. This treatment normalized plasma amino acids. She had intermittent emesis and anorexia, but was intellectually normal. Arginase enzyme assay and ARG1 sequencing and deletion/duplication analysis were normal. Treatments were stopped, but similar pattern of hyperaminoacidemia recurred. She also had hypercholesterolemia type IIa, with only elevated LDL cholesterol, despite an extremely lean body habitus. Exome sequencing was initially non-diagnostic. Through a literature search, we recognized the pattern of hyperaminoacidemia was strikingly similar to that reported in the Gcgr -/- knockout mice. Subsequently the patient was found to have an extremely elevated plasma glucagon and a novel, homozygous c.958_960del (p.Phe320del) variant in GCGR. Functional studies confirmed the pathogenicity of this variant. This case expands the clinical phenotype of GCGR defect in children and emphasizes the clinical utility of plasma amino acids in screening, diagnosis and monitoring glucagon signaling interruption. Early identification of a GCGR defect may provide an opportunity for potential beneficial treatment for an adult onset tumor predisposition disease.

Two Angelman families with unusually advanced neurodevelopment carry a start codon variant in the most highly expressed UBE3A isoform.

We present three children from two unrelated families with Angelman syndrome (AS) whose developmental skills are far more advanced than any other non-mosaic AS individual ever reported. All have normal gait and use syntactic language spontaneously to express their needs. All of them have a c.2T > C (p.Met1Thr) variant in UBE3A, which abrogates the start codon of isoform 1, but not of isoforms 2 and 3. This variant was maternally inherited in one set of siblings, but de novo in the other child from the unrelated family. This report underscores the importance of considering AS in the differential diagnosis even in the presence of syntactic speech.

Analysis of Copy Number Variants on Chromosome 21 in Down Syndrome-Associated Congenital Heart Defects.

One in five people with Down syndrome (DS) are born with an atrioventricular septal defect (AVSD), an incidence 2000 times higher than in the euploid population. The genetic loci that contribute to this risk are poorly understood. In this study, we tested two hypotheses: (1) individuals with DS carrying chromosome 21 copy number variants (CNVs) that interrupt exons may be protected from AVSD, because these CNVs return AVSD susceptibility loci back to disomy, and (2) individuals with DS carrying chromosome 21 genes spanned by microduplications are at greater risk for AVSD because these microduplications boost the dosage of AVSD susceptibility loci beyond a tolerable threshold. We tested 198 case individuals with DS+AVSD, and 211 control individuals with DS and a normal heart, using a custom microarray with dense probes tiled on chromosome 21 for array CGH (aCGH). We found that neither an individual chromosome 21 CNV nor any individual gene intersected by a CNV was associated with AVSD in DS. Burden analyses revealed that African American controls had more bases covered by rare deletions than did African American cases. Inversely, we found that Caucasian cases had more genes intersected by rare duplications than did Caucasian controls. We also showed that previously DS+AVSD (DS and a complete AVSD)-associated common CNVs on chromosome 21 failed to replicate. This research adds to the swell of evidence indicating that DS-associated AVSD is similarly heterogeneous, as is AVSD in the euploid population.

Clinical implications and considerations for evaluation of in silico algorithms for use with ACMG/AMP clinical variant interpretation guidelines.

Clinical genetics laboratories have recently adopted guidelines for the interpretation of sequence variants set by the American College of Medical Genetics (ACMG) and Association for Molecular Pathology (AMP). The use of in silico algorithms to predict whether amino acid substitutions result in human disease is inconsistent across clinical laboratories. The clinical genetics community must carefully consider how in silico predictions can be incorporated into variant interpretation in clinical practice.Please see related Research article: https://doi.org/10.1186/s13059-017-1353-5.

Caution in interpretation of disease causality for heterozygous loss-of-function variants in the MYH8 gene associated with autosomal dominant disorder.

To date, the NM_002472.2(MYH8):c.2021G>A (p.Arg674Gln) missense variant in the MYH8 gene is the only known genetic change in individuals with autosomal dominant trismus-pseudocamptodactyly syndrome with unknown molecular mechanism. Next-generation sequencing (NGS), including targeted gene panels and whole-exome sequencing, is routinely performed in many clinical diagnostic laboratories as standard-of-care testing aimed at identifying disease-causing genomic variants. Whole-exome sequencing has revealed loss-of-function variants in the MYH8 gene. To properly classify the MYH8 loss-of-function variants, we either retrieved them from public databases or retrospectively collected them from individuals genetically tested by custom NGS panels or by whole-exome sequencing and confirmed using Sanger sequencing. We further evaluated the respective clinical presentations of these individuals with the MYH8 loss-of-function variants. Heterozygous loss-of-function variants in the MYH8 gene were detected in 16 individuals without trismus-pseudocamptodactyly syndrome. Four of these 16 individuals had a pathogenic or likely pathogenic variant detected in another gene that could explain their clinical presentation. Moreover, there are ∼100 MYH8 heterozygous protein-truncating and splice site variants in the ExAC database in different populations. Our results, combined with the population data, indicate that loss-of-function variants in the MYH8 gene do not cause autosomal dominant trismus-pseudocamptodactyly syndrome, and the clinical significance of these variants remains unknown at present. This result highlights the importance of considering the molecular mechanism of disease, variants published in the medical literature, and population genomic data for the correct interpretation of loss-of-function variants in genes associated with autosomal dominant diseases.

Reassessment of Genomic Sequence Variation to Harmonize Interpretation for Personalized Medicine.

Accurate interpretation of DNA sequence variation is a prerequisite for implementing personalized medicine. Discrepancies in interpretation between testing laboratories impede the effective use of genetic test results in clinical medicine. To better understand the underpinnings of these discrepancies, we quantified differences in variant classification internally over time and those between our diagnostic laboratory and other laboratories and resources. We assessed the factors that contribute to these discrepancies and those that facilitate their resolution. Our process resolved 72% of nearly 300 discrepancies between pairs of laboratories to within a one-step classification difference and identified key sources of data that facilitate changes in variant interpretation. The identification and harmonization of variant discrepancies will maximize the clinical use of genetic information; these processes will be fostered by the accumulation of additional population data as well as the sharing of data between diagnostic laboratories.

Regulating whole exome sequencing as a diagnostic test.

In the last decade, there has been a flood of new technology in the sequencing arena. The onset of next-generation sequencing (NGS) technology has resulted in the vast increase in genetic diagnostic testing available to the ordering physician. Whole exome sequencing (WES) has become available as a diagnostic test performed in certified clinical laboratories. This has led to increased presence in the diagnostic marketplace, increased consumer awareness, and the question has been raised by various stakeholders to whether there is sufficient stringent regulation of WES and other NGS-based tests. We discuss the various WES services currently available in the marketplace, current regulation of WES as a laboratory developed test, the proposed FDA involvement in its oversight as well as the response of various laboratory groups that provide these diagnostic services. Overall, a rigorous process oversight and assessment of inter-lab reproducibility is strongly warranted for WES as it is used as a diagnostic test, but regulation should be mindful of the excessive administrative burden on academic and smaller diagnostic laboratories.

Gene Variant Databases and Sharing: Creating a Global Genomic Variant Database for Personalized Medicine.

Revolutionary changes in sequencing technology and the desire to develop therapeutics for rare diseases have led to the generation of an enormous amount of genomic data in the last 5 years. Large-scale sequencing done in both research and diagnostic laboratories has linked many new genes to rare diseases, but has also generated a number of variants that we cannot interpret today. It is clear that we remain a long way from a complete understanding of the genomic variation in the human genome and its association with human health and disease. Recent studies identified susceptibility markers to infectious diseases and also the contribution of rare variants to complex diseases in different populations. The sequencing revolution has also led to the creation of a large number of databases that act as "keepers" of data, and in many cases give an interpretation of the effect of the variant. This interpretation is based on reports in the literature, prediction models, and in some cases is accompanied by functional evidence. As we move toward the practice of genomic medicine, and consider its place in "personalized medicine," it is time to ask ourselves how we can aggregate this wealth of data into a single database for multiple users with different goals.

Genome-Wide Association Study of Down Syndrome-Associated Atrioventricular Septal Defects.

The goal of this study was to identify the contribution of common genetic variants to Down syndrome-associated atrioventricular septal defect, a severe heart abnormality. Compared with the euploid population, infants with Down syndrome, or trisomy 21, have a 2000-fold increased risk of presenting with atrioventricular septal defects. The cause of this increased risk remains elusive. Here we present data from the largest heart study conducted to date on a trisomic background by using a carefully characterized collection of individuals from extreme ends of the phenotypic spectrum. We performed a genome-wide association study using logistic regression analysis on 452 individuals with Down syndrome, consisting of 210 cases with complete atrioventricular septal defects and 242 controls with structurally normal hearts. No individual variant achieved genome-wide significance. We identified four disomic regions (1p36.3, 5p15.31, 8q22.3, and 17q22) and two trisomic regions on chromosome 21 (around PDXK and KCNJ6 genes) that merit further investigation in large replication studies. Our data show that a few common genetic variants of large effect size (odds ratio >2.0) do not account for the elevated risk of Down syndrome-associated atrioventricular septal defects. Instead, multiple variants of low-to-moderate effect sizes may contribute to this elevated risk, highlighting the complex genetic architecture of atrioventricular septal defects even in the highly susceptible Down syndrome population.

A 7-month-old male with Allan-Herndon-Dudley syndrome and the power of T3.

Allan-Herndon-Dudley syndrome (AHDS, MIM 300523) is an X-linked neurodegenerative disorder characterized by intellectual disability, severe hypotonia, diminished muscle mass, and progressive spastic paraplegia. All affected males have pathognomonic thyroid profiles with an elevated T3 , low-normal free T4 , and normal TSH. Mutations in the monocarboxylate transporter 8 (MCT8) gene, SLC16A2, have been found to be causative. Here, we describe a proband whose extensive evaluation and ultimate diagnosis of AHDS unmasked three previously undiagnosed generations of affected individuals in one family. This case illustrates the need for clinicians to consider obtaining full thyroid studies on individuals with the non-specific findings of severe hypotonia, failure to thrive, and gross motor delay.

Contribution of copy-number variation to Down syndrome-associated atrioventricular septal defects.

PURPOSE: The goal of this study was to identify the contribution of large copy-number variants to Down syndrome-associated atrioventricular septal defects, the risk for which in the trisomic population is 2,000-fold more as compared with that of the general disomic population. METHODS: Genome-wide copy-number variant analysis was performed on 452 individuals with Down syndrome (210 cases with complete atrioventricular septal defects; 242 controls with structurally normal hearts) using Affymetrix SNP 6.0 arrays, making this the largest heart study conducted to date on a trisomic background. RESULTS: Large, common copy-number variants with substantial effect sizes (OR > 2.0) do not account for the increased risk observed in Down syndrome-associated atrioventricular septal defects. By contrast, cases had a greater burden of large, rare deletions (P < 0.01) and intersected more genes (P < 0.007) as compared with controls. We also observed a suggestive enrichment of deletions intersecting ciliome genes in cases as compared with controls. CONCLUSION: Our data provide strong evidence that large, rare deletions increase the risk of Down syndrome-associated atrioventricular septal defects, whereas large, common copy-number variants do not appear to increase the risk of Down syndrome-associated atrioventricular septal defects. The genetic architecture of atrioventricular septal defects is complex and multifactorial in nature.

A comprehensive genomic approach for neuromuscular diseases gives a high diagnostic yield.

OBJECTIVE: Neuromuscular diseases (NMDs) are a group of >200 highly genetically as well as clinically heterogeneous inherited genetic disorders that affect the peripheral nervous and muscular systems, resulting in gross motor disability. The clinical and genetic heterogeneities of NMDs make disease diagnosis complicated and expensive, often involving multiple tests. METHODS: To expedite the molecular diagnosis of NMDs, we designed and validated several next generation sequencing (NGS)-based comprehensive gene panel tests that include complementary deletion and duplication testing through comparative genomic hybridization arrays. Our validation established the targeted gene panel test to have 100% sensitivity and specificity for single nucleotide variant detection. To compare the clinical diagnostic yields of single gene (NMD-associated) tests with the various NMD NGS panel tests, we analyzed data from all clinical tests performed at the Emory Genetics Laboratory from October 2009 through May 2014. We further compared the clinical utility of the targeted NGS panel test with that of exome sequencing (ES). RESULTS: We found that NMD comprehensive panel testing has a 3-fold greater diagnostic yield (46%) than single gene testing (15-19%). Sanger fill-in of low-coverage exons, copy number variation analysis, and thorough in-house validation of the assay all complement panel testing and allow the detection of all types of causative pathogenic variants, some of which (about 18%) may be missed by ES. INTERPRETATION: Our results strongly indicate that for molecular diagnosis of heterogeneous disorders such as NMDs, targeted panel testing has the highest clinical yield and should therefore be the preferred first-tier approach.