Familial paroxysmal nonkinesigenic dyskinesia

Familial paroxysmal nonkinesigenic dyskinesia is a disorder of the nervous system that causes periods of involuntary movement. Paroxysmal indicates that the abnormal movements come and go over time. Nonkinesigenic means that episodes are not triggered by sudden movement. Dyskinesia broadly refers to involuntary movement of the body.

People with familial paroxysmal nonkinesigenic dyskinesia experience episodes of abnormal movement that develop without a known cause or are brought on by alcohol, caffeine, stress, fatigue, menses, or excitement. Episodes are not induced by exercise or sudden movement and do not occur during sleep. An episode is characterized by irregular, jerking or shaking movements that range from mild to severe. In this disorder, the dyskinesias can include slow, prolonged contraction of muscles (dystonia); small, fast, "dance-like" motions (chorea); writhing movements of the limbs (athetosis); and, rarely, flailing movements of the limbs (ballismus). Dyskinesias also affect muscles in the trunk and face. The type of abnormal movement varies among affected individuals, even among members of the same family. Individuals with familial paroxysmal nonkinesigenic dyskinesia do not lose consciousness during an episode. Most people do not experience any other neurological symptoms between episodes.

Individuals with familial paroxysmal nonkinesigenic dyskinesia usually begin to show signs and symptoms of the disorder during childhood or their early teens. Episodes typically last 1-4 hours, and the frequency of episodes ranges from several per day to one per year. In some affected individuals, episodes occur less often with age.

Familial paroxysmal nonkinesigenic dyskinesia is a very rare disorder. Its prevalence is estimated to be 1 in 5 million people.

Mutations in the PNKD gene cause familial paroxysmal nonkinesigenic dyskinesia. The function of the protein produced from the PNKD gene is unknown; however, it is similar to a protein that helps break down a chemical called methylglyoxal. Methylglyoxal is found in alcoholic beverages, coffee, tea, and cola. Research has demonstrated that this chemical has a toxic effect on nerve cells (neurons). It remains unclear if the PNKD gene is related to the breakdown of methlglyoxal. How mutations in the PNKD gene lead to the signs and symptoms of familial paroxysmal nonkinesigenic dyskinesia is also unknown.

Read more about the PNKD gene.

This condition is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is typically sufficient to cause the disorder. Almost everyone with a mutation in the PNKD gene will develop familial paroxysmal nonkinesigenic dyskinesia. In all reported cases, an affected person has inherited the mutation from one parent.