Introduction
In recent years, there has been a significant expansion in the availability of genetic testing alternatives. The utilization of next-generation sequencing (NGS) and disease gene panels increases the necessity of gene selection for sequencing purposes. The determination of inheritance mode (autosomal dominant versus recessive) with a precise molecular diagnosis has the potential to impact various aspects such as prognosis, disease progression, and the screening of comorbidities.
Why Is Genetic Testing Important in Neuromuscular Junction Disease?
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Genetic testing is important for NMD diagnosis and management due to cost, illness management, quality of life, family planning, and clinical trial participation.
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Molecular diagnosis is cost-effective since it replaces a diagnostic journey and avoids wasteful conventional therapy.
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NMDs are often difficult to diagnose and require a thorough workup to generate a diagnosis hypothesis. MRIs, electromyography, muscle and nerve biopsies, lumbar puncture, PET/CT scans, and thorough blood testing would be performed. Even after all these tests, a diagnosis may not be reached, and NMD patients are often given expensive treatments that could be dangerous, like high-dose intravenous steroids, IVIG, chemotherapy, and plasma exchange, which are used on an unexplained basis.
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Genetic testing using appropriate gene panels may be more likely to diagnose NMD; therefore, it should be the primary alternative if everything else fails.
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Another cost-effective benefit of genetic testing is that if other family members have similar observable characteristics or traits, they can be saved from the diagnostic process and may only need a single confirmatory genetic test.
The reason for genetic testing in NMD is illness management.
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Multisystemic NMDs can cause major but preventable problems with the presence of multiple medical conditions, such as Limb-girdle muscular dystrophy (LGMD). Type 1B is a genetic disorder characterized by, which can be avoided by installing a heart rhythm monitor.
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In other circumstances, molecular diagnosis may induce focused screening that affects the quality of life (for example, myotonic dystrophy, which is a genetic disorder characterized by muscle weakness and wasting, as well as various other symptoms affecting multiple body systems with diabetes and early cataract (clouding of the eye-lens) screening molecular diagnosis can influence treatment decisions.
What Are the Links Between Psychological and Genetic Testing?
Psychological well-being is an underestimated but vital part of genetic testing in NMD such as:
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Rare genetic diseases are usually diagnosed five to seven years later. The families experience severe mental distress and lower health-related quality of life.
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Genetic testing can improve quality of life by speeding diagnosis.
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Disease inheritance patterns are essential for genetic counseling and family planning.
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A genetic diagnosis may include spouse carrier testing, in vitro fertilization with preimplantation diagnosis and selection, postnatal screening, and screening of unaffected family members.
What Are the Different Types of Genetic Testing?
The practitioner must choose from various genetic testing, which can be difficult. The genetic testing would include both hypothesis-driven and shotgun methods. The theory-driven testing uses a genetic test to assess if the NMD is affecting an individual based on presentation and neuromuscular examination findings. In contrast, a shotgun approach implies the practitioner feels the NMD is hereditary without knowing the gene or panel of genes affected and wants to explore as many alternatives as possible to discover an explanation. Genetic tests fall into seven categories such as:
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Single gene tests (examine alterations specifically inside a single gene.)
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Illness panels.
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Nucleotide repeat expansion testing.
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Mitochondrial DNA sequencing (the process of decoding mitochondrial DNA.)
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Whole exome sequencing (involves the comprehensive analysis of the protein-coding regions of an individual's genome.)
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Copy number variation (refers to a type of genetic variation that involves the presence of different numbers of copies of a certain DNA segment in the genome of an individual.)
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Whole genome sequencing (the process of determining the complete DNA sequence of an organism's genome).
What Is Hypothesis-Driven Genetic Testing?
Individual gene tests were the first sequence of an individual gene using Sanger sequencing, which reads a continuous piece of DNA one base at a time.
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Single-gene testing is accurate, although the amount of base pairs read at once is a constraint. Not all large genes, introns, and other noncoding regions are read.
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Single gene testing commonly targets gene mutation hotspots or locations recognized from literature to be often mutated in disease.
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Single-gene tests are beneficial when the practitioner is confident in a diagnosis and utilizes genetic testing to confirm it.
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NGS also improves gene sequencing depth and coverage, discovering novel gene variations not previously connected with a disease.
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NGS technology is the basis for gene panels, the most popular genetic testing for NMD. Panels detect single nucleotide variations, minor insertions and deletions, and bigger copy number variants, such as exon deletions, with great coverage.
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A disease gene panel test may be relevant because more than 20 genes have been identified as causal when altered.
What Are the Drawbacks?
Gene panels are the most popular genetic testing for NMD. However, they have drawbacks.
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A panel's genes determine its quality. Due to delays between when a novel mutation is confirmed as causal and when genetic testing laboratories add it to their panels, panels change from year to year.
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The mitochondrial genome is a distinct DNA pool.
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MT-TK mutations cause myoclonus epilepsy with ragged red fibers (MERRF), a mitochondrial disease.
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In sequencing mitochondrial DNA, mitochondrial malfunction is suspected.
What Is a Shotgun Approach to Genomics?
Some NMDs do not have a recognized gene, so a non-typical sickness is a possibility.
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Despite the fact that a rational hypothesis has not been confirmed, the practitioner may assume that sickness is inherited. In other cases, hypothesis-driven approaches are supplanted with shotgun approaches.
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The most popular shotgun genomic test is whole exome sequencing.
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While WES (whole exome sequencing) sequences all exons at the same time, it does not find noncoding regions, mitochondrial DNA, or repetitive expansions.
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WES is more expensive than disease gene panels, but the shotgun approach speeds up diagnosis.
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In WES, results are negative, and the practitioner believes a genetic etiology, karyotype, or chromosomal microarray testing may be required to identify severe chromosomal abnormalities.
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WES cannot detect large deletions, duplications, or translocations detected by these approaches. Despite the fact that chromosomal abnormalities are uncommon in NMDs, this test is critical for genetic testing.
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WES is the most effective clinical shotgun genomic testing technology.
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Whole genome sequencing is becoming more common as deeper sequencing technology becomes more affordable. WGS (whole-genome sequencing) is not recommended for therapeutic purposes at this time.
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We discuss it because WGS may eventually replace all genetic testing. WGS is present in existing NMDs.
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By sequencing the entire genome, WGS identifies single-nucleotide variants, small insertions and deletions, copy number variants, and structural differences such as repeat expansions.
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WGS use is now discouraged because of cost and interpretation.
Conclusion
Neuromuscular diseases can affect multiple organs and systems, making them extremely complex. Although there are currently several biomarkers to aid in the diagnosis of IN MD, the expertise of the clinician is still vital. Since some markers are frequently changed in many different disorders in similar ways, the physical examination ought to be the initial step toward generating clinical suspicion. The simplest method of diagnosis to date is the whole neuromuscular examination, followed by other assessments. However, some biomarkers are linked to particular diseases, and identifying them can be essential to making a diagnosis. Given the wide spectrum of serum and urine abnormalities seen in clinical practice, it is not uncommon to meet doctors who are unfamiliar with rare diseases while dealing with IN MD. Therefore, having a thorough understanding of these abnormalities helps speed up the diagnostic process and facilitate the referral to neuromuscular problem specialists.
