SNP Shot: Genomic Insights

Sporadic hemiplegic migraine (SHM) is an uncommon type of migraine. Migraines are characterized by severe, throbbing pain, usually on one side of the head. Individuals may also experience nausea, vomiting, and sensitivity to light and noise. These recurring headaches usually start during childhood or the teenage years and can be triggered by factors such as certain foods, stress, or minor head injuries. Each headache can last anywhere from a few hours to several days.

In SHM, and in some other migraine types, an "aura" – a set of neurological symptoms – precedes the headache. Common aura symptoms include temporary visual disturbances like blind spots (scotomas), flashing lights, zig-zag lines, and double vision. Auras in SHM are also marked by temporary numbness or weakness, often affecting one side of the body (hemiparesis). Other aura symptoms may include speech difficulties, confusion, and sleepiness. Typically, an aura develops gradually over several minutes and lasts for approximately one hour.

Some individuals with SHM experience particularly severe migraine episodes. These can involve fever, extended periods of weakness, seizures, and even coma. While most people with SHM recover completely between episodes, neurological symptoms like memory loss and concentration problems can persist for weeks or months. Some affected individuals develop mild, but permanent, coordination problems (ataxia) that can worsen over time, along with involuntary, rapid eye movements (nystagmus). Intellectual disability, ranging from mild to severe, has been reported in some cases of SHM.

Inheritance:

"Sporadic" signifies that the condition appears in individuals with no family history of it. Most cases arise from new (de novo) genetic mutations that probably occur during early development of the embryo. However, some individuals inherit the genetic mutation responsible for SHM from a parent who is not affected. (This lack of symptoms despite carrying the mutation is known as reduced penetrance.) While family members of someone with SHM don't have SHM themselves, they may experience regular migraines without hemiparesis. A similar condition, familial hemiplegic migraine (FHM), presents with the same symptoms as SHM but affects multiple family members.