The disease What is SELENON‑RM?
SELENON (formerly SEPN1)-Related Myopathy (SELENON-RM) is a group of rare progressive congenital disorders that impair the body’s ability to synthesize Selenoprotein N1. In order for a child to inherit SELENON-RM, both parents must carry a mutated copy of the gene encoding SELENON.
Clinically, SELENON-RM shares similarities with other congenital muscular dystrophies (CMD), particularly those characterized by spinal rigidity. However, distinguishing features such as axial muscle weakness and early-onset respiratory insufficiency, even in ambulatory individuals, differentiate SELENON-RM from other CMDs.
Infants born with SELENON-RM often present with hypotonia (reduced muscle tone leading to ‘floppiness’) and delayed gross motor milestones, such as rolling over or crawling. Muscle weakness is typically most pronounced in the neck and trunk, which can make simple tasks—like raising the head, sitting, standing, or transitioning between positions—difficult or impossible without assistance. Muscle weakness might also affect chewing and swallowing, with some individuals needing feeding tubes to maintain adequate nutrition.
Although most individuals with SELENON-RM will learn to walk, spinal rigidity and rapidly progressing scoliosis can limit mobility. Additionally, respiratory complications from diaphragm weakness often emerge early, leading to nocturnal hypoventilation. Children as young as one year old might require ventilatory support during sleep to maintain adequate oxygen levels.
