Clinical and genetic characteristics and diagnostic features of Landouzy–Dejerine facioscapulohumeral muscular dystrophy

Landouzy–Dejerine facioscapulohumeral muscular dystrophy (FSHD) is one of the most common hereditary myodystrophies. A study of the genetic nature of the disease, which has an autosomal dominant mode of inheritance, is extremely interesting and revealing. A unique structure of D4Z4 macrosatellite repeats found in the 4q35 region was originally characterized by a decrease in the number of repeats in patients with Landouzy–Dejerine muscular dystrophy, which resulted in the activation of neighboring genes, in particular, the DUX4 transcription factor. Later, it was found that the epigenetic mechanisms responsible for the chromatin condensation of this region underlie the activation. To date, additional participants leading to pathogenesis of the disease, such as SMCHD1 methylation regulator and DBE-T regulatory long noncoding RNA, have been identified. The revealed complexity of the disease mechanisms is in good agreement with the observed pattern of the disease inheritance. The study of the Landouzy–Dejerine muscular dystrophy pathogenesis is a good example of how monogenic diseases can possess a more complex nature of inheritance.