How 5q SMA is Inherited
5q SMA is passed from parents to their children through faulty SMN1 genes. It usually follows an autosomal recessive pattern of inheritance which means it is passed from parents to their children through faulty SMN1 genes. This means that:
- People who inherit two faulty copies of the SMN1 gene (one from each parent) have SMA.
- People who inherit one faulty copy and one healthy copy of the SMN1 gene (one from each parent) are carriers of SMA. Around 1 in 40 people are carriers of SMA; carriers do not have SMA or any symptoms of SMA.
- People who inherit two healthy copies of the SMN1 gene (one from each parent) do not have SMA and are not carriers.
Though most inherit SMA from both parents, for around 2% of people the mutation is new, most likely due to an error in the DNA of the egg or sperm cell from which they were conceived. This is called a de novo mutation.
It is important that family members understand the results of the genetic testing that has led to the diagnosis of SMA. Genetic counselling should take place with a healthcare professional who has expert training in genetics. They will answer any questions families may have about the genetic aspects of the diagnosis and provide information on the possible options for future pregnancies.
If you would like to read more information about genetics and how a person may inherit SMA, please go to the inheritance page we have provided in addition to this Section (see appendix 1). You may also like to visit the “Useful Resources” Section which lists patient organisations available in various countries.