A new gene involved in myopathies
Jan. 17, 2013
For a long time, tubular aggregate myopathy is an orphan disease, the origin of which was still unknown. Today, thanks to researchers of the IGBMC, the gene at the origin of the disease has been discovered. These results published on 17th January in the journal American Journal of Human Genetics offer new hope for the diagnosis and development of targeted therapies.
Tubular aggregates in muscle cells
Under the name “myopathies” are brought together a thousand of diseases characterised by a muscular weakness. Myopathies are present in all kind of population and can affect both children and adults. Most of these diseases have a genetic cause. In spite of important scientific progress thanks to the support of associations like the Association française contre les myopathies (AFM), the gene in cause is still unknown for several myopathies, preventing an efficient genetic diagnosis and increasing the risk of recurrence in affected families. Among them, the tubular aggregate myopathy is characterized by a morphological anomaly of muscular fibers, showing an accumulation of membrane tubules with regular arrays. Besides, these aggregates also appear as secondary symptoms in many muscular disorders as exercice-induced cramps or alcohol- and drug-induced myopathies. They also accumulate in muscle with age in healthy people.
Deep sequencing to identify the “sick” gene
Johann Böhm from Jocelyn Laporte’s team at the IGBMC has focused on tubular aggregate myopathy, in collaboration with the Pitié-Salpêtrière Hospital and the Faculty of Medicine of Marseille. To detect the gene responsible for the disease, researchers have first led an important work to characterize patients in order to gather families affected by the genetic form of the disease. Thanks to DNA high-throughput sequencing, their exome (the sum of all expressed genes, representing around 1.5% of the genome) has been sequenced in about 3 weeks to reveal the gene responsible for the disease: dominant mutations in STIM1 were responsible for the tubular aggregate myopathy. STIM1 is a key factor the regulation of calcium, a major messenger in muscular contraction. Indeed, it enables to measure and modulate the muscular level of calcium. It was already known that loss of this protein was responsible for a severe immunodeficiency syndrome associated to a muscular hypotonia. Conversely, in the case of patients affected with the tubular aggregate myopathy, STIM1 is hyperactivated, leading to an alteration of calcium homeostasis that would be responsible for the development of aggregates in muscular cells and muscular weakness.
New therapeutic opportunities
These results are particularly important since many myopathies are caused by a dysfunction of mechanisms regulating calcium. Some therapeutic molecules are already used to modulate calcium, predicting a short term development of targeted therapies for the treatment of the tubular aggregate myopathy that might be widened to other pathologies with similar symptoms.