Mutational Spectrum Analysis of Neurodegenerative Diseases and Its Pathogenic Implication

A spinal muscular atrophy modifier implicates the SMN protein in SNARE complex assembly at neuromuscular synapses

Reduced survival motor neuron (SMN) protein triggers the motor neuron disease, spinal muscular atrophy (SMA). Restoring SMN prevents disease, but it is not known how neuromuscular function is preserved. We used model mice to map and identify an Hspa8G470R synaptic chaperone variant, which suppressed SMA. Expression of the variant in the severely affected mutant mice increased lifespan >10-fold, improved motor performance, and mitigated neuromuscular pathology. Mechanistically, Hspa8G470R altered SMN2 splicing and simultaneously stimulated formation of a tripartite chaperone complex, critical for synaptic homeostasis, by augmenting its interaction with other complex members. Concomitantly, synaptic vesicular SNARE complex formation, which relies on chaperone activity for sustained neuromuscular synaptic transmission, was found perturbed in SMA mice and patient-derived motor neurons and was restored in modified mutants. Identification of the Hspa8G470R SMA modifier implicates SMN in SNARE complex assembly and casts new light on how deficiency of the ubiquitous protein causes motor neuron disease.

Missense MED12 variants in 22 males with intellectual disability: From nonspecific symptoms to complete syndromes

We describe the phenotype of 22 male patients (20 probands) carrying a hemizygous missense variant in MED12. The phenotypic spectrum is very broad ranging from nonspecific intellectual disability (ID) to the three well-known syndromes: Opitz-Kaveggia syndrome, Lujan-Fryns syndrome, or Ohdo syndrome. The identified variants were randomly distributed throughout the gene (p = 0.993, χ² test), but mostly outside the functional domains (p = 0.004; χ² test). Statistical analyses did not show a correlation between the MED12-related phenotypes and the locations of the variants (p = 0.295; Pearson correlation), nor the protein domain involved (p = 0.422; Pearson correlation). In conclusion, establishing a genotype-phenotype correlation in MED12-related diseases remains challenging. Therefore, we think that patients with a causative MED12 variant are currently underdiagnosed due to the broad patients' clinical presentations.

A Systematic and Comprehensive Review on Disease-Causing Genes in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder and is characterized by degeneration and axon loss from the upper motor neuron, that descends from the lower motor neuron in the brain. Over the period, assorted outcomes from medical findings, molecular pathogenesis, and structural and biophysical studies have abetted in providing thoughtful insights underlying the importance of disease-causing genes in ALS. Consequently, numerous mechanisms were proposed for the pathogenesis of ALS, considering protein mutations, aggregation, and misfolding. Besides, the answers to the majority of ALS cases that happen to be sporadic still remain obscure. The application in discovering susceptibility factors in ALS contemplating the genetic factors is to be further dissevered in the future years with innovation in research studies. Hence, this review targets in revisiting the breakthroughs on the disease-causing genes related with ALS.