Identification of a new gene involved in myopathies
nstead of being straight, the Z line, which ensures the integrity of the contractile units, appears as a sawtooth in these myopathy patients.
Acta Neuropathol Mar 2019
Jan. 30, 2019
In this study, researchers from Jocelyn Laporte's team at the IGBMC (CNRS/Inserm/University of Strasbourg) characterized a new subclass of congenital myopathy and identified mutations in ACTN2 as the genetic cause. This gene codes for alpha-actinin 2, which is involved in the maintenance of the muscle structure and ensures proper contractile function. These results, published on January 30, 2019 in the journal Acta Neuropathologica, open up new hopes for the development of targeted therapies.
Congenital myopathies are a group of genetic diseases affecting the structure of the muscle fibre. These abnormalities lead to a decrease in muscle strength and can occur from birth. More than 30 genes involved in the appearance or transmission of congenital myopathies have already been identified, but half of the patients still remain without genetic diagnosis.
Muscle fibres are composed of contractile units that produce strength. The integrity and stability of these units is ensured by a structure called the Z line. In this study, co-directed by Jocelyn Laporte and Johann Böhm and in close collaboration with Norma Romero’s team (Institut de Myologie, Paris), the researchers observed very specific defects. In the muscles of the patients the Z-lines have an abnormal structure and show a zigzag pattern. Following these observations, they identified de novo mutations (i.e., one that does not exist in parents) in alpha-actinin 2, an essential component of the Z line.
To validate these results, the researchers conducted experiments in two animal models. They overexpressed the mutant protein in zebrafish and the researchers observed that these fish swim less well and travel shorter distances. These anomalies correlated with structural muscle defects. In mice, researchers used a viral vector to express the mutant gene in the tibialis anterior muscle. Again, they observed structural defects similar to those found in patients' muscles and they measured decreased muscle strength in the animals.
These studies highlight a unique congenital myopathy at the clinical, histological and genetic levels and improves molecular diagnosis in patients with rare muscle diseases.
This study was funded by the ANR, the Foundation for Rare Diseases, the Foundation for Medical Research and the French Association against Myopathies.