X-Linked Dystonia-Parkinsonism

Clinical characteristics: Individuals with X-linked dystonia-parkinsonism (XDP) have dystonia of varying severity and parkinsonism. XDP afflicts primarily Filipino men and, rarely, women. The mean age of onset in men is 39 years; the clinical course is highly variable with parkinsonism as the initial presenting sign, overshadowed by dystonia as the disease progresses. Features of parkinsonism include resting tremor, bradykinesia, rigidity, postural instability, and severe shuffling gait. The dystonia develops focally, most commonly in the jaw, neck, trunk, and eyes, and less commonly in the limbs, tongue, pharynx, and larynx, the most characteristic being jaw dystonia often progressing to neck dystonia. Individuals with pure parkinsonism have non-disabling symptoms that are only slowly progressive; those who develop a combination of parkinsonism and dystonia can develop multifocal or generalized symptoms within a few years and die prematurely from pneumonia or intercurrent infections. Female carriers are mostly asymptomatic, though a small minority may manifest dystonia, parkinsonism, or chorea.

Diagnosis/testing: The diagnosis of XDP is suspected in a male with typical clinical findings, family history consistent with X-linked inheritance, and maternal ancestral roots from the Panay Islands in the Philippines. Molecular genetic testing for variants that tag a disease-associated haplotype of the multilocus transcript system termed TAF/DYT3 is required to confirm the diagnosis in those with no known family history of XDP, very early symptoms, and/or a phenotype of pure parkinsonism, pure tremor, or chorea without dystonia. Olfactory testing indicates olfactory dysfunction early in the disease and may be used to support the diagnosis when molecular genetic testing is not available.

Management: Treatment of manifestations: Pharmacologic agents are used to treat dystonia or parkinsonism or both. Anticholinergic agents, benzodiazepines, and sometimes neuroleptics are used in the early stages of dystonia; zolpidem and tetrabenazine are used after dystonia becomes multifocal or generalized. Botulinum toxin injections improve focal dystonia but may worsen swallowing in individuals with preexisting dysphagia. Parkinsonism is treated with levodopa and dopamine agonists to control tremor. Bilateral pallidal deep brain stimulation may be used to treat advanced disease and medically refractory dystonia, although it may have less effect on parkinsonism.

Prevention of secondary complications: Swallowing evaluation to guide diet modification and swallowing techniques to minimize risk of aspiration. Physical therapy, coupled with maximal medical and surgical therapy, may help delay immobility and its complications.

Surveillance: Annual clinical evaluations in males with the disease-related haplotype who are not yet symptomatic, biannual evaluation for symptomatic males to monitor medications, and periodic swallowing evaluation, especially in those with subjective dysphagia.

Genetic counseling: XDP is inherited in an X-linked manner. Approximately 94% of affected individuals have a known family history of the condition. De novo occurrence of the disease-related haplotype associated with the disorder has not been observed to date. Males with XDP pass the TAF1/DYT3 disease-associated haplotype to all of their daughters and none of their sons. Women who are carriers have a 50% chance of transmitting the TAF1/DYT3 disease-associated haplotype in each pregnancy: males who inherit the TAF1/DYT3 disease-associated haplotype will be affected; females who inherit the TAF1/DYT3 disease-associated haplotype are mostly asymptomatic, although a small percentage may manifest symptoms. Carrier evaluation of at-risk female relatives is possible if the TAF1/DYT3 disease-associated haplotype has been identified in the family. Once the TAF1/DYT3 disease-associated haplotype has been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic diagnosis for XDP are possible. Caution should be exercised in interpreting the results of prenatal testing as the c.94C>T (p.Arg32Cys) variant that marks the disease haplotype has not been proven to be the molecular cause of XDP.