Incidental findings on array comparative genomic hybridization: detection of carrier females of dystrophinopathy without any family history

Long-Read Sequencing Revealed Extragenic and Intragenic Duplications of Exons 56-61 in DMD in an Asymptomatic Male and a DMD Patient

Expanded carrier screening (ECS) has become an increasingly common technique to assess the genetic risks of individuals in the prenatal or preconception period. Unexpected variants unrelated to referral are being increasingly detected in asymptomatic individuals through ECS. In this study, we reported an asymptomatic male with duplication of exons 56-61 in the DMD gene through ECS using whole-exome sequencing (WES), which was also detected in a male patient diagnosed with typical Duchenne muscular dystrophy (DMD). Breakpoint analysis was then performed to explore the potential mechanisms of phenotypic differences using long-read sequencing (LRS), PacBio single-molecule real-time (PacBio SMRT) target sequencing, and Sanger sequencing. Complex structural variations (SVs) on chromosome X were identified in the asymptomatic male, which revealed that the duplication occurred outside the DMD gene; whereas, the duplication in the patient with DMD was a tandem repeat. The phenotypic differences between the two men could be explained by the different breakpoint junctions. To the best of our knowledge, this is the first report of a breakpoint analysis of DMD duplication in two men with different phenotypes. Breakpoint analysis is necessary when the clinical phenotypes are inconsistent with genotypes, and it applies to prenatal testing.

EMQN best practice guidelines for genetic testing in dystrophinopathies

Dystrophinopathies are X-linked diseases, including Duchenne muscular dystrophy and Becker muscular dystrophy, due to DMD gene variants. In recent years, the application of new genetic technologies and the availability of new personalised drugs have influenced diagnostic genetic testing for dystrophinopathies. Therefore, these European best practice guidelines for genetic testing in dystrophinopathies have been produced to update previous guidelines published in 2010.These guidelines summarise current recommended technologies and methodologies for analysis of the DMD gene, including testing for deletions and duplications of one or more exons, small variant detection and RNA analysis. Genetic testing strategies for diagnosis, carrier testing and prenatal diagnosis (including non-invasive prenatal diagnosis) are then outlined. Guidelines for sequence variant annotation and interpretation are provided, followed by recommendations for reporting results of all categories of testing. Finally, atypical findings (such as non-contiguous deletions and dual DMD variants), implications for personalised medicine and clinical trials and incidental findings (identification of DMD gene variants in patients where a clinical diagnosis of dystrophinopathy has not been considered or suspected) are discussed.

Maternal copy-number variations in the DMD gene as secondary findings in noninvasive prenatal screening

PURPOSE

Noninvasive prenatal screening (NIPS) using genome sequencing also reveals maternal copy-number variations (CNVs). Those CNVs can be clinically actionable or harmful to the fetus if inherited. CNVs in the DMD gene potentially causing dystrophinopathies are among the most commonly observed maternal CNVs. We present our experience with maternal DMD gene CNVs detected by NIPS.

METHODS

We analyzed the data of maternal CNVs detected in the DMD gene revealed by NIPS.

RESULTS

Of 26,123 NIPS analyses, 16 maternal CNVs in the DMD gene were detected (1/1632 pregnant women). Variant classification regarding pathogenicity and phenotypic severity was based on public databases, segregation analysis in the family, and prediction of the effect on the reading frame. Ten CNVs were classified as pathogenic, four as benign, and two remained unclassified.

CONCLUSION

NIPS leverages CNV screening in the general population of pregnant women. We implemented a strategy for the interpretation and the return of maternal CNVs in the DMD gene detected by NIPS.

An atypical autistic phenotype associated with a 2q13 microdeletion: a case report

Background

Autism spectrum disorders are serious neurodevelopmental disorders that affect approximately 1% of the population. These disorders are substantially influenced by genetics. Several recent linkage analyses have examined copy number variations associated with autism risk. Microdeletion of the 2q13 region is considered a pathogenic copy number variation. This microdeletion is involved in developmental delays, congenital heart defects, dysmorphism, and various psychiatric disorders, including autism spectrum disorders. There are only 34 reported cases with this chromosomal deletion, and five cases of autism spectrum disorders have been identified among them. The autistic phenotype associated with this microdeletion has never been described.

Case presentation

We describe the case of a 44-month-old Caucasian girl with the 2q13 microdeletion and autism spectrum disorders with global development delay but no associated organ anomalies. We examined the autistic phenotype using different workups and observed an atypical phenotype defined by relatively preserved relational competency and imitation abilities.

Conclusions

The main contribution of this case report is the precise description of the autistic phenotype in the case of this deletion. We observed some atypical clinical features that could be markers of this genetic anomaly. We have discussed the pathophysiology of autism associated with this microdeletion and its incomplete penetrance and variable expressivity.

Prenatal diagnosis of congenital myopathies and muscular dystrophies

Congenital myopathies and muscular dystrophies constitute a genetically and phenotypically heterogeneous group of rare inherited diseases characterized by muscle weakness and atrophy, motor delay and respiratory insufficiency. To date, curative care is not available for these diseases, which may severely affect both life-span and quality of life. We discuss prenatal diagnosis and genetic counseling for families at risk, as well as diagnostic possibilities in sporadic cases.

Genetic counselling difficulties and ethical implications of incidental findings from array-CGH: a 7-year national survey

Microarray-based comparative genomic hybridization (aCGH) is commonly used in diagnosing patients with intellectual disability (ID) with or without congenital malformation. Because aCGH interrogates with the whole genome, there is a risk of being confronted with incidental findings (IF). In order to anticipate the ethical issues of IF with the generalization of new genome-wide analysis technologies, we questioned French clinicians and cytogeneticists about the situations they have faced regarding IF from aCGH. Sixty-five IF were reported. Forty corresponded to autosomal dominant diseases with incomplete penetrance, 7 to autosomal dominant diseases with complete penetrance, 14 to X-linked diseases, and 4 were heterozygotes for autosomal recessive diseases with a high prevalence of heterozygotes in the population. Therapeutic/preventive measures or genetic counselling could be argued for all cases except four. These four IF were intentionally not returned to the patients. Clinicians reported difficulties in returning the results in 29% of the cases, mainly when the question of IF had not been anticipated. Indeed, at the time of the investigation, only 48% of the clinicians used consents mentioning the risk of IF. With the emergence of new technologies, there is a need to report such national experiences; they show the importance of pre-test information on IF.

Diagnostic use of Massively Parallel Sequencing in Neuromuscular Diseases: Towards an Integrated Diagnosis

Massively parallel sequencing is revolutionizing the genetic testing in diagnosis laboratories, replacing gene-by-gene investigations with a "gene panel" strategy. This new approach is particularly promising for the diagnosis of neuromuscular disorders affecting children as well as adults, which is constrained by strong clinical and genetic heterogeneity. While it leads to a strong improvement in molecular diagnosis, this new approach is dramatically changing the whole diagnosis process, establishing new decision trees and requiring integrated strategies between clinicians and laboratories. To have an overview of the implementation and benefit of these novel sequencing strategies for the diagnosis of neuromuscular disorders, we surveyed the current literature on the application of targeted genes panel sequencing, exome sequencing and genome sequencing. We highlight advantages and disadvantages of these different strategies in a diagnosis setting, discuss about unresolved cases, and point potential validation approaches and outcomes of massively parallel sequencing. It appears important to integrate such novel strategies with clinical, histopathological and imaging investigations, for a faster and more accurate diagnosis and patient care, and to foster research projects and clinical trials.

Incidental Findings with Genomic Testing: Implications for Genetic Counseling Practice

This paper summarizes the current controversies surrounding the identification and disclosure of "incidental" or "secondary" findings from genomic sequencing and the implications for genetic counseling practice. The rapid expansion of clinical sequencing has influenced the ascertainment and return of incidental findings, while empiric data to inform best practices are still being generated. Using the North Carolina Clinical Genomic Evaluation by Next Generation Exome Sequencing (NCGENES) research project as an example, we discuss the implications of different models of consent and their impact on patient decisions.