Congenital Dystrophies - Neuromuscular Disorders Precision Medicine: Genomics to Care and Cure

The muscle unit structure has been used to classify neuromuscular disorders (NMDs) according to the site of involvement. The four main muscle unit components involve the: 1) Neuronal Anterior Horn Cell (AHC). 2) Nerve Fiber (axon) transmitting the signal from the AHC to the skeletal muscle fibers. 3) Neuromuscular junction (NMJ) (the cleft between nerve fiber’s endings and muscle sarcolemma membrane). 4) Contractile unit (muscle belly that contains several muscle bundles; every bundle has 100-1000 muscle fibers). The myofibrils (muscle fibers) are the most complex component in terms of the extensive number of proteins that code for the myofibers’ proteins and molecules. Spinal muscular atrophy (SMA) presents the well-known AHC-related muscular diseases. The group of axons-related NMDs (Neuropathy), called “Charcot Marie Tooth (CMT) diseases”, involves several subtypes and are of different inheritance pattern. The NMJ-related NMDs is collectively named as “Myathenias”, of which are the congenital myathenic syndromes. The muscle tissues (myofibrils) are associated with the most extensive group of muscle diseases. Congenital muscular dystrophies (CMDs) and congenital myopathies are primary muscle diseases that appear since birth and run progressive severe courses. Neuromyology is currently a neurology sub-specialization that is highly effective in better clinical identification of such significant genetically heterogeneous and clinically overlapping groups of NMDs and CMDs. The advances in sequencing technologies have contributed towards uncovering the widerange of genetic heterogeneity in NMDs. To date, over 600 genes were characterized in association with congenital myopathies, dystrophies, and NMDs.

The future is holding truly promising cures for NMDs’ patients, through the emerging gene therapies, however its extremely high cost challenges the possibility for large-scale applications.

Neuromuscular disorders (NMDs) present a large group of primary muscle weakness’ diseases that progressively affect the subjects’ walking and movements’ abilities. Associated extra-muscular involvements constitute chronic co-morbidities that disturb the patients’ quality of life. There are challenges to better serve NMDs’ chronic patients that require a multidisciplinary team of health care providers. Hence, it is of importance to discuss what approaches are taken to ensure high quality integrated-health measures that aim at advancing the standard care and management plans for these patients in Qatar. The tertiary prevention approach of carrier and prenatal detection or the primary prevention applying the preimplantation genetic diagnosis has a principal role in reducing the recurrence of NMDs in our families and community. Hence, the question up for discussion is whether our prevention genetic program serves the needs for such families. Newborn screening is implemented in Qatar for a pre-designed list of diseases. The panel discussion will address the potential need for a tailored screening program for treatable types of congenital dystrophies or myopathies. Moreover, patients’ voices are known to have a powerful influence on the heath authorities’ decision-making. Patient advocacy groups are groups dedicated to taking patient’s voices to the forefront, these groups are well acting worldwide, and so are we ready to start this experience here in Qatar?

In the early 90s, in the wake of the discovery of the dystrophin gene, many international research groups embarked on a lengthy and tedious gene hunt for many remaining neuromuscular diseases. The Middle East and the MENA region as a whole soon appeared as goldmines in that respect. The high degree of consanguinity and the presence of multiplex families with rare disorders were ideal conditions to elucidate hereditary diseases at the molecular level, especially the recessive ones (limb girdle muscular dystrophies, congenital muscular dystrophies, congenital myopathies and congenital myasthenic syndromes). Genethon and the Institut de Myologie, two French institutions funded by the French Muscular Dystrophy Association (AFM-Telethon) played at the time a pivotal role in establishing strong partnerships with local partners (in Morocco, Turkey, Lebanon, Iran, Kuwait and Oman; notably). These collaborations took several forms: on-site visits with clinics and bedside teaching, joint research projects and attendance to the Summer School of Myology in Paris. The harvest and the return on investment turned out to be quite impressive shedding more light on this part of the world where awareness and knowledge about neuromuscular disorders had been scarce and limited for quite some time. Over the years, our objectives slowly switched from molecular diagnosis to daily management of patients and nowadays to innovative therapies. What is currently happening in Spinal Muscular Atrophy and Duchenne Muscular Dystrophy are perfect examples of this change in paradigm.

Myopathies in pediatrics require comprehensive assessment of the affected child. One of these assessments is related to muscles’ signal and atrophic changes which are easily detected by MRI screening. This requires only a limited study of the whole body; hence, integration of a battery of investigations including MRI imaging that could be very helpful with the diagnosis and follow up, as well.

The autosomal recessive Congenital Muscular Dystrophies associated with a merosin deficiency, also known as type 1A muscular dystrophy (MDC1A), results from mutations of the LAMA2 gene. This large gene, composed of 65 exons, encodes the a2-chain subunit of laminin-2 (merosin). For many years, identification of the lack of expression of merosin on muscle biopsies was considered to initiate a molecular analysis by conventional Sanger sequencing. In the majority of cases (80%), the two pathogenic mutations were directly identified by this approach. Nevertheless, for the remaining cases with a single or no mutation, complementary approaches were necessary. They include the detection of large rearrangement; either by MLPA or CGH-array and the search for deep intronic mutations impacting splicing through the mRNA analysis. Altogether, these approaches allowed for the identification of disease-causing mutations in more than 95% of families. Since these early days, patients with partial loss of merosin have been identified. This has paved the way to the identification of a wide range of phenotypes associated with mutations of the LAMA2 gene, ranging from the most severe forms in patients with hypotonia at birth or in the first weeks of life, to rare patients achieving independent ambulation. Most patients, among those with partial laminin-a2 deficiency, belong to this last category. The identification of those milder phenotypes have also led to higher difficulty to select which genes have to be analyzed based on the clinical presentation. This led to the development of NGS gene panels in order to simultaneously screen all genes reported to be associated with congenital muscular dystrophies. Thus, in a single NGS experiment, it is now possible to screen the 19 most commonly involved genes and thus limit the diagnostic wandering. This new technology, while being able to rapidly deliver the sequence of all genes, also place the geneticist in front of multiple candidate mutations, which need to be evaluated prior to reporting the identification of the disease-causing mutation(s) in a family. Not considering the need for large data storage capacity, it is now mandatory to have access to efficient bioinformatics systems and to trained geneticists. In this presentation, I will demonstrate the benefits and limits of this approach for the diagnosis of DMC.

The mission of Cure CMD is to promote research directed to find a cure for the Congenital Muscular Dystrophies (CMD). Cure CMD, a patient advocacy organization, was founded in 2008 by three parents whose children were affected by understudied forms of CMDs. Just before the end of the 20th century, the genes and coded proteins responsible for the clinicopathological presentations of CMD started to be revealed. Merosin or laminin 211 was the first dysfunctional protein identified in western cases of CMD. Later, a lack of another protein, collagen VI, was found to cause a different type of CMD. Today, it is recognized that the five main subtypes of CMD involve proteins in four locations of the muscle cell: the extracellular matrix (ECM) where laminin 211 and collagen VI reside (LAMA2-CMD and ColVI-CMD); the ECM-sarcoplasm interface where the á-dystroglycan is the affected protein, either, as a consequence of mutations in its coding gene (primary Dystroglycanopathy) or mutations in various glycosyltransferase proteins (secondary Dystroglycanopathies); the sarcoplasmic reticulum, location of the SEPN1 protein (Selenon or SEPN1-CMD); and the intranuclear membrane where the mutated protein lamin A/C provokes the CMD subtype (LMNA or L-CMD).

The CMDs are a clinically and genetically heterogeneous group of NMDs. The symptoms are evident at birth or before the second birthday. They present progressive weakness and hypotonia and share characteristic biopsy findings. Several disease-related complications include nutritional deficiencies due to feeding difficulties, joint contractures, and respiratory insufficiency. In some cases, heart complications and cognitive impairment, are also present. Promising developments in biotechnology and a deeper understanding of the underlying pathophysiological mechanisms responsible for the different CMD types have facilitated design potential therapeutic schemes targeted at molecular, and biochemical pathways. Through close collaboration with researchers, clinicians, patients, families, dedicated volunteers, other foundations and donors, Cure CMD, has achieved significant impact in its first decade as a nonprofit organization: launched two clinical trials; completed a five-year natural history study with the NIH to characterize clinical trial endpoints; grew the Congenital Muscle Disease International Registry (CMDIR) with approximately 3,000 registrants worldwide and, funded over $2 million in research grants. We will describe tools and programs Cure CMD has to offer to accelerate the “bench-to-bedside” translation of therapies.

Spinal Muscular Atrophies are neurodegenerative disorders that are common in our region. In fact, they are the second most common autosomal recessive disorder. The incidence is 1 per 10,000. Genetically, caused by defects in the Survival Motor Neuron (SMN) gene on chromosome 5q. There are two types of SMN, SMN1 and SMN2. 95% of SMA patients have abnormality in SMN1; whereas SMN2 acts as a phenotypic modifier. The search for a cure has been a long journey. Promising therapeutic options have become available. Despite this progress, management of children/adults with SMA faces some big challenges. The success of the management pathway relies heavily on “multidisciplinary” input and the experience of care providers.

Infantile hypotonia is a common presenting symptom. There are various causes for neonatal hypotonia including systemic illness such as sepsis and congenital cardiac disease among others. With regards to neurological hypotonia, CNS disorders such as metabolic disorders, brain malformations and neonatal encephalopathy including hypoxic ischemic encephalopathy and early epileptic encephalopathy are among the important causes. Neuromuscular disorders form an important group of disorders that should be actively sought and evaluated in neonates presenting with hypotonia; with new treatments available for patients with spinal muscular atrophy (SMA) and congenital myasthenia, which makes early screening and diagnosis essential for good care given the effectiveness of the treatments available including gene therapy. The importance of genetic counseling and prevention of recurrence is also imperative in conditions that have a specific treatment such as Merosin deficient congenital muscular dystrophy and similar disorders. This presentation will discuss the common causes of hypotonia in neonates and young infants and a diagnostic scheme for such children with some guidance on the priority of testing and evaluation.

Mitochondrial diseases are clinically and genetically heterogeneous and tissue specific presentations are common. It is not known to date why different mitochondrial DNA (mtDNA) or mutations in nuclear genes encoding mitochondrial proteins result in very heterogeneous clinical presentations. The most common causes of mitochondrial diseases in adults are mutations in the mtDNA. A defect of mitochondrial protein synthesis results in respiratory chain deficiency in patients with common mttRNA mutations (such as m.3243A>G). Mutations in nuclear genes involved in mitochondrial translation affect ubiquitously expressed genes, but the result is highly tissue specific symptoms suggesting that there are additional factors, which contribute to the tissue specificity in mitochondrial translation deficiencies. Most of these gene defects result in early-onset, severe, and often fatal diseases. The diagnosis of mitochondrial diseases has changed significantly, as next generation sequencing technologies become widely available. Although diagnosing mitochondrial disorders require special clinical assessment, and sometimes biochemical analyses, there is now a strong rationale to perform first-line whole genome sequencing in mitochondrial diseases. This can accelerate the speed of diagnosis and prevent expensive and invasive investigations.

Metabolic myopathy is referred to a rare group of inherited muscle diseases caused by specific enzymatic defects that lead to muscle energy defect and subsequently muscle dysfunction. They are divided into disorders of carbohydrate metabolism, disorders of lipid metabolism and mitochondrial disorders. Examples of the common metabolic myopathies are Pompe disease, McArdle’s disease, beta-oxidation defects and carnitine disorders. A unique clinical presentation should raise the suspicion of such rare muscle disorders specially when the patient has episodic muscle dysfunction and dynamic rather than static symptoms. Premature exertional fatigue and exercise-associated muscle cramps are other clues. However, they occasionally present as progressive muscle weakness mimicking dystrophic muscles disorders or multiorgan involvement. Early diagnosis and implementation of therapeutic strategy will help prevent acute muscle dysfunction, myoglobinurea and rhabdomyolysis. This strategy may include avoiding vigorous exercise and prolonged fasting, eating complex carbohydrates, carnitine and MCT supplementation and enzyme replacement therapy.