Rigid spine muscular dystrophy (RSMD) is a form of congenital muscular dystrophy that is characterized by spinal stiffness, weakness in muscles of the torso and neck, and breathing problems very early in life.
The genetic cause of RSMD
RSMD is caused by mutations in the SELENON (SEPN1) gene. The SELENON gene codes for a protein called selenoprotein N. While this protein’s function is not fully clear, selenoprotein N is thought to be required for muscle tissue formation before birth.
The SELENON gene is located on chromosome 1, which is an autosomal (non-sex) chromosome. Chromosomes are structures within the cell that store genetic information. Humans have 22 pairs of autosomal chromosomes, and one pair of sex chromosomes. Mutations in autosomal chromosomes can affect both males and females equally.
How is RSMD inherited?
RSMD is inherited in an autosomal recessive manner. We all inherit two copies of each gene found on autosomal chromosomes, one copy coming from the father and one from the mother. In autosomal recessive diseases such as RSMD, symptoms are seen when both genes copies have mutations. People with only one mutated copy are known as “carriers,” and do not usually show disease symptoms. However, carriers can pass the disease onto their children.
If one copy of the SELENON gene is mutated in each parent, meaning they are both disease carriers, the predicted outcomes for each pregnancy are:
- A 25% chance of the child being born without RSMD.
- A 50% chance of the child being a carrier.
- A 25% chance of the child being affected by RSMD.
These mutations can be detected by genetic testing. Genetic counselors can explain inheritance patterns, so as to help parents make informed family decisions.
Last updated: August 28, 2019
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