A case report of adolescent myofibrillar myopathy due to a R406W pathogenic variant in desmin with symptoms of "hypertrophic cardiomyopathy".

Objective: Myofibrillar myopathies (MFM) are a group of sporadic and inherited progressive skeletal muscle disorders that can lead to physical disability and premature death. To date, pathogenic variants in different genes are associated with MFM. MFM induced by variants in the Desmin () gene is the most common subtype of MFM.

Case Presentation: A 15-year-old boy with MFM was described, whose symptoms first presented as cardiac symptoms. Enlarged right and left atria, thickened ventricular septal (IVS) and mild mitral (MR) and tricuspid regurgitation (TR) in the echocardiography were found. Atrial fibrillation, intermittent atrioventricular (AV) block, ST-T changes in the dynamic electrocardiogram (ECG) were shown. Mild myopathic changes in the electromyographic exam were detected. Ultrastructural analysis found slight Z-line changes and a few small myolysis lesions, but no abnormal inclusion bodies. Genetic testing detected a heterozygous missense variant (c.1216C > T) of DES, and 2 rare variants: (c.1102C > G) and (c.3074G > A). The patient's parents didn't show skeletal and cardiac muscle disorders. DNA sequencing analysis showed no variant of was carried by them. Thus, we detected a case of MFM caused by de novo variant c.1216C > T/p.Arg406Trp with predominantly myocardial alterations.