Skeletal abnormalities, pediatric-onset severe osteoporosis, and multiple fragility fractures in a patient with a novel CTNNB1 de novo variant.

We report a case of a patient with a de novo germline heterozygous truncating variant of CTNNB1 gene (c.2172del, p.Tyr724Ter) causing neurodevelopmental disorder with spastic diplegia and visual defects syndrome (NEDSDV) associated with a new clinical feature - severe pediatric-onset osteoporosis and multiple fractures. A functional effect of the identified variant was demonstrated using adipose-tissue derived primary mesenchymal stem cells, where we detected the alteration of CTNNB1mRNA and ß-catenin protein levels using real-time PCR and Western blot analysis.

Desmin mutations result in mitochondrial dysfunction regardless of their aggregation properties.

Desmin, being a major intermediate filament of muscle cells, contributes to stabilization and positioning of mitochondria. Desmin mutations have been reported in conjunction with skeletal myopathies accompanied by mitochondrial dysfunction. Depending on the ability to promote intracellular aggregates formation, mutations can be considered aggregate-prone or non-aggregate-prone. The aim of the present study was to describe how expression of different desmin mutant isoforms effects mitochondria and contributes to the development of myocyte dysfunction. To achieve this goal, two non-aggregate-prone (Des S12F and Des A213V) and four aggregate-prone (Des L345P, Des A357P, Des L370P, Des D399Y) desmin mutations were expressed in skeletal muscle cells. We showed that all evaluated mutations affected the morphology of mitochondrial network, suppressed parameters of mitochondrial respiration, diminished mitochondrial membrane potential, increased ADP/ATP ratio, and enhanced mitochondrial DNA (mtDNA) release. mtDNA was partially secreted through exosomes as demonstrated by GW4869 treatment. Dysfunction of mitochondria was observed regardless the type of mutation: aggregate-prone or non-aggregate-prone. However, expression of aggregate-prone mutations resulted in more prominent phenotype. Thus, in this comparative study of six pathogenic desmin mutations that cause skeletal myopathy development, we confirmed a role of mitochondrial dysfunction and mtDNA release in the pathogenesis of desmin myopathies, regardless of the aggregation capacity of the mutated desmin.