Question: How many people are affected by sporadic hemiplegic migraine ?
Answer: The worldwide prevalence of sporadic hemiplegic migraine is unknown. Studies suggest that in Denmark about 1 in 10,000 people have hemiplegic migraine and that the condition occurs equally in families with multiple affected individuals (familial hemiplegic migraine) and in individuals with no family history of the condition (sporadic hemiplegic migraine).
Source: GHR

Question: What are the genetic changes related to sporadic hemiplegic migraine ?
Answer: Mutations in the ATP1A2 and CACNA1A genes have been found to cause sporadic hemiplegic migraine. The proteins produced from these genes transport charged atoms (ions) across cell membranes. The movement of these ions is critical for normal signaling between nerve cells (neurons) in the brain and other parts of the nervous system. Signaling between neurons relies on chemicals called neurotransmitters, which are released from one neuron and taken up by neighboring neurons. Mutations in the ATP1A2 and CACNA1A genes disrupt the transport of ions in neurons, which is thought to impair the normal release and uptake of certain neurotransmitters in the brain. The resulting abnormal signaling may lead to the severe headaches and auras characteristic of sporadic hemiplegic migraine. Many people with sporadic hemiplegic migraine do not have a mutation in one of the known genes. Researchers believe that mutations in other genes are also involved in the condition, although these genes have not been identified. There is little evidence that mutations in the CACNA1A and ATP1A2 genes play a role in common migraines, which affect millions of people each year. Researchers are searching for additional genetic changes that may underlie rare types of migraine, such as sporadic hemiplegic migraine, as well as the more common forms of migraine.
Source: GHR