Lochmüller Lab

Rhabdomyolysis is an acute failure of cellular homeostasis characterized by acute skeletal muscle damage triggered by trauma, infection, drugs, or strenuous exercise. Recurrent rhabdomyolysis is a complication in several neuromuscular diseases (NMDs), including muscular dystrophies, metabolic muscle disorders and disorders of calcium homeostasis. It causes the release of intracellular muscle components into the bloodstream leading to myoglobinuria and in some cases renal failure.

This study discovers a novel genetic cause of rhabdomyolysis due to a variant in the ATP2A2 gene that affects the function of the intracellular calcium pump SERCA2, resulting in dysregulated skeletal muscle homeostasis. The identification of this novel variant advances the understanding of autosomal dominant rhabdomyolysis and provides real-world impact through a diagnostic conclusion for three generations of affected individuals across three unrelated families included in the study.

Authors and collaboration information:

Our new collaborative study, “Dominant rhabdomyolysis linked to a recurrent ATP2A2 variant reducing SERCA2 function in muscle” published recently in Brain: a journal of neurology is authored by lab PhD student Malaichamy Sivasankar and postdoctoral researcher Dr Romane Idoux, with contributions from lab members Dr Kiran Polavarapu, Dr Rachel Thompson, Dr Sally Spendiff, Ricardo Carmona and Daniel O’Neil and former postdoc Dr Emily Freeman. Dr Hanns Lochmuller is senior author, alongside Dr Nicol Voermans, Dr Andreas Roos and Dr Ivo Baric.

About the Study

Through analysis of the genomic and phenotypic data of 15 individuals affected by recurrent rhabdomyolysis from three unrelated families – two from Croatia and Hungary analysed through the RD-Connect-Genome Phenome Analysis Platform (GPAP) and one from the Netherlands identified through international collaboration – we identified a novel genetic cause of this disorder. Initial whole-genome sequencing analysis had failed to uncover a causative variant in any known rhabdomyolysis or NMD-associated genes, but an expanded re-analysis identified a rare heterozygous missense variant (p.R528Q) in the ATP2A2 gene which was present in all affected individuals. The missense variant is absent in gnomAD control populations and in-silico 3D modelling using AlphaFold showed loss of salt bridges with glutamic acid (Glu412) and aspartic acid (Asp567) when positively charged arginine (Arg528) is substituted by neutral charged glutamine. While ATP2A2 has previously been associated with genetic skin diseases, this is the first time that it has been shown to cause rhabdomyolysis. In our study we identified the variant and performed functional analysis in cell and zebrafish models to show its effect.

Ultrastructural analysis by transmission electron microscopy in skeletal muscle showed mild myopathic changes in patient muscle, and SERCA2 protein quantification showed normal levels. However, patient myotubes exhibited altered kinetics of Ca²⁺ transients, with a delayed time to reach the Ca²⁺ peak and slower Ca²⁺ reuptake, supporting SERCA dysfunction in patients affected by the rare ATP2A2 variant.

We created an atp2a2a morphant zebrafish which showed morphological and locomotor defects, with results from further experiments confirming these defects were because of the knockdown of the atp2a2a gene. We then established a zebrafish model expressing the specific human ATP2A2 to determine whether the ATP2A2 p.R528Q variant is associated with the neuromuscular clinical phenotype described in patients. These results revealed that the morphological and locomotor activity data obtained for the fish co-injected with the mutant RNA were significantly comparable to those measured in zebrafish where atp2a2a has been knocked down, meaning that the ATP2A2 p.R528Q variant is responsible for the skeletal muscle defect in zebrafish.

Outcome

The discovery of this novel cause of rhabdomyolysis not only provides new insights into a disease mechanism that extends beyond the genetic variant in ATP2A2, but also ends a decades-long diagnostic odyssey for these families, provides a means for other at-risk individuals to be identified, and potentially suggests future therapeutic options.

Reference

Malaichamy, S., Idoux, R., Polavarapu, K., Šikić, K., Holla, E., Thompson, R., Spendiff, S., Schänzer, A., Kusters, B., Freeman, E., Hentschel, A., O’Neil, D., Carmona-Martinez, R., Dobelmann, V., Tucht, C., Schouten, M., Ruck, T., Schara-Schmidt, U., Kamsteeg, E. J., Ramadža, D. P., … Lochmüller, H. (2025). Dominant rhabdomyolysis linked to a recurrent ATP2A2 variant reducing SERCA2 function in muscle. Brain : a journal of neurology, awaf067. Advance online publication. https://doi.org/10.1093/brain/awaf067

Click here to access the accepted manuscript.