DSS is caused by changes (mutations) in several different genes. Genes associated with DSS include MPZ, EGR2, PMP22, and PRX. Mutations in these genes can result in the continued loss of myelin (the protective sheath surrounding nerves) leading to muscle weakness and mobility problems. Not all genes associated with DSS have been identified. For about 45% of individuals diagnosed with DSS, the genetic cause of the condition has been determined. This may indicate that other genes not yet identified could also be associated with DSS.
DSS can be inherited in a dominant or recessive manner. Individuals with a dominant form of the condition may have earlier symptom onset compared to individuals with the recessive form.
Dominant genetic disorders occur when only a single copy of a non-working gene is necessary to cause a particular disease. The non-working gene can be inherited from either parent or can be the result of a mutated (changed) gene in the affected individual. The risk of passing the non-working gene from an affected parent to an offspring is 50% for each pregnancy. The risk is the same for males and females.
Recessive genetic disorders occur when an individual inherits a non-working gene from each parent. If an individual receives one working gene and one non-working gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the non-working gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier, like the parents, is 50% with each pregnancy. The chance for a child to receive working genes from both parents is 25%. The risk is the same for males and females.