SMA is a progressive, rare genetic disease that is caused by a missing or malfunctioning survival motor neuron 1 (SMN1) gene. Although spinal muscular atrophy is a rare disease, it is the number one genetic cause of infant death.
Fortunately, this disease does not affect cognitive development or function.
To develop this disease, an individual must inherit two defective SMN 1 genes, one from each parent. If both parents are carriers and therefore have a defective SMN1 gene, they usually do not know or show any manifestation of the disease. Approximately 1 in every 40th person in the population is a carrier. However, even if such two carriers meet, it does not necessarily mean that their children will suffer from this disease. There is “only” a 25% chance.
So what child is born to two carriers:
- There is a 25% probability that a child with SMA will be born
- There is a 50% probability that an SMA carrier will be born
- There is a 25% probability that the child will not have SMA and will not be an SMA carrier