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Dyskinesias (Paroxysmal)
Genetics The paroxysmal dyskinesias, including paroxysmal kinesigenic dyskinesia (PKD), non-kinesigenic dyskinesia (PNKD), exertion-induced dyskinesia (PED), and hypnogenic dyskinesia (PHD), are usually idiopathic (primary) conditions that occur for unknown reasons. Idiopathic PKD, PNKD, PED, or PHD may be familial, with autosomal dominant inheritance, or appear to occur randomly for unknown reasons (sporadically). The paroxysmal dyskinesias, however, may occur secondary to other underlying disorders, conditions, or other factors. Genetic studies have mapped some but not all families of PKD to chromosome 16 (16p11.2-q11.2). This region overlaps with that of another autosomal dominant disorder known as familial infantile convulsions and paroxysmal choreoathetosis (ICCA syndrome). The disorder is characterized by seizures during infancy and transient, non-kinesigenic episodes of involuntary movement. Some researchers suggest that these disorders may result from different mutations of the same gene or mutations of different genes within this chromosomal region. In other patients with idiopathic PKD, there is no apparent family history of the disease. Researchers suggest that such cases may be due to spontaneous (sporadic) genetic mutations that occurred for unknown reasons. In addition, some apparently sporadic cases may actually have been inherited; according to some investigators, this may be suggested by the fact that there are no apparent differences between familial and sporadic PKD regarding the frequency and duration of episodes, nature of the involuntary movement patterns (phenomenology), or response to treatment. Although many reports indicate that most cases of PKD are familial, other investigators suggest that sporadic (and secondary or symptomatic) disease may be more common than previously recognized. Genetic analysis of a large multigenerational Italian family with PNKD with an autosomal dominant pattern of inheritance mapped the PNKD gene to chromosome 2 (2q33-q35). Although most reported cases of PNKD are familial, sporadic disease may actually be more common. In patients with idiopathic PNKD without a positive family history of the disease, PNKD may be caused by new genetic mutations that occurred for unknown reasons. There may be certain differences between familial and sporadic PNKD; sporadic cases tend to be characterized by a greater variability in the age at symptom onset, similar frequency of occurrence of the disease in males and females, short-lasting episodes that may have a duration of seconds, a higher frequency of episodes; and no premonitory sensations before the onset of the attacks. Some have suggested that sporadic PNKD may be underreported due to the challenges involved in establishing this diagnosis, including the apparent lack of family history and the need to differentiate PNKD from psychogenic movement disorders. A psychogenic disease is one in which symptoms have a mental or an emotional basis rather than an organic origin. Paroxysmal exertion-induced dyskinesia (PED) and paroxysmal hypnogenic dyskinesia (PHD) are usually sporadic (idiopathic), although rare familial cases have been described. In addition to the paroxysmal dyskinesias, there has been an intense interest in the genetics of episodic ataxias, another group of disorders characterized by intermittent motor dysfunction (table). Paroxysmal dyskinesias: Genetics
ICCA = infantile convulsions with paroxysmal dyskinesias 
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