Pediatric Nemaline Myopathy: A Systematic Review Using Individual Patient Data

A Case of a Newborn With Nemaline Myopathy From Al-Qunfudhah City, Saudi Arabia

Nemaline myopathy is a primary skeletal muscle disorder and one of the congenital myopathies. It can be caused by mutations in at least 12 genes, with the nebulin (NEB) gene being the most common. Here, we present the first case of a neonate with nemaline myopathy from Al-Qunfudhah, Saudi Arabia. A full-term baby boy was delivered via cesarean section due to decreased fetal movement. The baby was covered with a thick meconium stain. He was born with severe distress and underwent an endotracheal tube placement. The baby presented generalized muscle weakness, hypotonia, and areflexia. Examination revealed arthrogryposis, bilateral small chin, undescended testicle, joint deformity, hip dislocation, and clubfoot. Chest examination revealed conducting sound and bilateral equal air entry. Moreover, he experienced bilateral chest wheeze and conducting sound. All laboratory tests were normal, and whole-exome sequencing revealed pathogenic homozygous splice acceptor variant NEB gene c.8889+1G˃A. The patient was first suspected to have spinal muscular atrophy as there was no previous nemaline myopathy case reported from Al-Qunfudhah. However, the typical symptoms and genetic sequencing confirmed his condition. As the society in Al-Qunfudhah is known for consanguinity, as in our case, clinicians should identify other types of myopathy as it is expected to occur in further cases.

Muscle cofilin alters neuromuscular junction postsynaptic development to strengthen functional neurotransmission

Cofilin, an actin severing protein, plays critical roles in muscle sarcomere addition and maintenance. Our previous work has shown Drosophila cofilin (DmCFL) knockdown causes progressive deterioration of muscle structure and function and produces features seen in nemaline myopathy (NM) caused by cofilin mutations. We hypothesized that disruption of actin cytoskeleton dynamics by DmCFL knockdown would impact other aspects of muscle development, and, thus, conducted an RNA sequencing analysis which unexpectedly revealed upregulated expression of numerous neuromuscular junction (NMJ) genes. We found that DmCFL is enriched in the muscle postsynaptic compartment and that DmCFL deficiency causes F-actin disorganization in this subcellular domain prior to the sarcomere defects observed later in development. Despite NMJ gene expression changes, we found no significant changes in gross presynaptic Bruchpilot active zones or total postsynaptic glutamate receptor levels. However, DmCFL knockdown results in mislocalization of glutamate receptors containing the GluRIIA subunit in more deteriorated muscles and neurotransmission strength is strongly impaired. These findings expand our understanding of cofilin's roles in muscle to include NMJ structural development and suggest that NMJ defects may contribute to NM pathophysiology.

A Rare Case Report of Dental and Craniofacial Manifestations of Nemaline Myopathy

Any congenital muscular disorder can cause severe dental and craniofacial deformity. The clinicians must understand the aetiology of this muscular disorder to plan the treatment for this condition. Currently, there is limited data available in the literature on the dental manifestation of nemaline myopathy. Nemaline myopathy is a type of rare congenital muscular disorder characterized by severe dental and craniofacial deformity. This case report describes the dental and craniofacial manifestations of such diseases in an eight-year-old child who visited the unit of pediatric and preventive dentistry with a chief complaint of irregular placement of teeth and inability to close the mouth.

Congenital Nemaline Myopathy in Two Neonates With Different Mutations: A Case Series and Literature Review

Nemaline myopathy is a skeletal muscle disorder characterized by a wide range of severity and variable presentation. While most cases present in the neonatal period with symptoms, such as hypotonia, muscle weakness, and respiratory insufficiency, delayed onset in childhood or adulthood is also observed. The pathogenesis of nemaline myopathy involves at least 12 genes, and the condition can arise from de novo mutations or be inherited in a dominant or recessive manner. In this study, we present two cases of neonates admitted to a neonatal intensive care unit (NICU) exhibiting hypotonia, muscle weakness, and respiratory insufficiency. Both cases were diagnosed with congenital nemaline myopathy, with each patient displaying distinct mutations. This report highlights the clinical and genetic heterogeneity of this condition, emphasizing the importance of early recognition and genetic evaluation for accurate diagnosis and appropriate management of affected individuals.

Drosophila Tropomodulin is required for multiple actin-dependent processes within developing myofibers

Proper muscle contraction requires the assembly and maintenance of sarcomeres and myofibrils. Although the protein components of myofibrils are generally known, less is known about the mechanisms by which they individually function and together synergize for myofibril assembly and maintenance. For example, it is unclear how the disruption of actin filament (F-actin) regulatory proteins leads to the muscle weakness observed in myopathies. Here, we show that knockdown of Drosophila Tropomodulin (Tmod), results in several myopathy-related phenotypes, including reduction of muscle cell (myofiber) size, increased sarcomere length, disorganization and misorientation of myofibrils, ectopic F-actin accumulation, loss of tension-mediating proteins at the myotendinous junction, and misshaped and internalized nuclei. Our findings support and extend the tension-driven self-organizing myofibrillogenesis model. We show that, like its mammalian counterpart, Drosophila Tmod caps F-actin pointed-ends, and we propose that this activity is crucial for cellular processes in different locations within the myofiber that directly and indirectly contribute to the maintenance of muscle function. Our findings provide significant insights to the role of Tmod in muscle development, maintenance and disease.