Question: What is (are) Familial hemiplegic migraine ?
Answer: Familial hemiplegic migraine (FHM) is a form of migraine headache that runs in families. Migraines usually cause intense, throbbing pain in one area of the head, often accompanied by nausea, vomiting, and extreme sensitivity to light and sound. These recurrent headaches typically begin in childhood or adolescence and may last from a few hours to a few days. People with familial hemiplegic migraine experience an aura that comes before the headache. The most common symptoms associated with an aura are temporary visual changes such as blind spots (scotomas), flashing lights, zig-zagging lines, and double vision. In people with familial hemiplegic migraine, auras are also characterized by temporary numbness or weakness, often affecting one side of the body (hemiparesis). An aura typically develops gradually over a few minutes and lasts about an hour. Researchers have identified three forms of familial hemiplegic migraine known as FHM1, FHM2, and FHM3. Each of the three types is caused by mutations in a different gene.
Source: GARD

Question: What are the symptoms of Familial hemiplegic migraine ?
Answer: What are the signs and symptoms of Familial hemiplegic migraine? The Human Phenotype Ontology provides the following list of signs and symptoms for Familial hemiplegic migraine. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Abnormality of movement 90% Hemiplegia/hemiparesis 90% Incoordination 50% Nystagmus 50% Abnormality of retinal pigmentation 7.5% EEG abnormality 7.5% Neurological speech impairment 7.5% Sensorineural hearing impairment 7.5% The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.
Source: GARD