Rigid spine muscular dystrophy
Rigid spine muscular dystrophy (RSMD) is a form of congenital muscular dystrophy characterized by early-onset muscle weakness, spine stiffness, and serious respiratory complications.
Overview
Rigid spine muscular dystrophy (RSMD) is a form of congenital muscular dystrophy. Disorders in this group cause muscle weakness and wasting (atrophy) beginning very early in life. In particular, RSMD involves weakness of the muscles of the torso and neck (axial muscles). Other characteristic features include spine stiffness and serious breathing problems.
In RSMD, muscle weakness is often apparent at birth or within the first few months of life. Affected infants can have poor head control and weak muscle tone (hypotonia), which may delay the development of motor skills such as crawling or walking. Over time, muscles surrounding the spine atrophy, and the joints of the spine develop deformities called contractures that restrict movement. The neck and back become stiff and rigid, and affected children have limited ability to move their heads up and down or side to side. Affected children eventually develop an abnormal curvature of the spine. In some people with RSMD, muscles in the inner thighs also atrophy, although it does not impair the ability to walk.
A characteristic feature of RSMD is breathing difficulty (respiratory insufficiency) due to restricted movement of the torso and weakness of the diaphragm, which is the muscle that separates the abdomen from the chest cavity. The breathing problems, which tend to occur only at night, can be life-threatening. Many affected individuals require a machine to help them breathe (mechanical ventilation) during sleep.
Frequency
RSMD is thought to be a rare disorder, although its prevalence is unknown.
Causes
Mutations in a gene called SELENON (formerly SEPN1) cause about 40 percent of cases of RSMD. When caused by mutations in this gene, the condition is known as rigid spine muscular dystrophy 1 (RSMD1). The genetic cause of the remainder of cases is unknown.
The SELENON gene provides instructions for making a protein known as selenoprotein N. While its specific job is unknown, researchers suspect it plays a role in the formation of muscle tissue before birth and is important for normal muscle function after birth. The gene mutations that cause RSMD1 are thought to reduce the amount of selenoprotein N or impair its activity in cells.
Gene Associated with Rigid Spine Muscular Dystrophy
- SELENON
Inheritance
This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
Other Names for This Condition
- Congenital muscular dystrophy with spine rigidity syndrome
- Muscular dystrophy, congenital, merosin-positive, with early spine rigidity
- Rigid spinal muscular dystrophy
- Rigid spine congenital muscular dystrophy
- RSMD