Phenotypic characterization of PIGN-associated paroxysmal dyskinesia in Soft-coated wheaten terriers and preliminary response to acetazolamide therapy

A hereditary movement disorder in Soft coated wheaten terriers (SCWT) has been associated with a mutation in PIGN which encodes an enzyme involved in synthesis of glycosylphosphatidylinositol (GPI). The objective of this study was to describe and classify the clinical phenotype and assess therapeutic response. Twenty-five SCWT and related dogs homozygous for PIGN:c.398C>T with paroxysmal dyskinesia were available for inclusion. Medical records and video recordings of 17 dogs were evaluated in a retrospective case series. Affected dogs had episodes of involuntary, hyperkinetic movements and dystonia. Median age of onset was 2.5 years. A typical episode consisted of rapid, irregular hyperflexion and extension of the pelvic limbs with some degree of truncal dystonia. A mild episode consisted of spontaneous flexion of one pelvic limb while walking which could resemble a lameness. Episodes lasted several minutes to several hours and occurred up to 10 times/day or more. They were not associated with exercise or fasting but were sometimes triggered by excitement or stress. Acetazolamide therapy improved nine of 11 dogs, in seven cases abolishing episodes. Five of 17 dogs treated with other agents had mild improvement with clonazepam (n = 2), levetiracetam (n = 1), or phenobarbital (n = 2). Paroxysmal dyskinesias must be differentiated from seizure disorders since they often respond to different therapies. The SCWT phenotype consisted predominantly of hyperkinesia, and can respond dramatically to acetazolamide. GPI anchors proteins to the cell surface including carbonic anhydrase IV which modulates synaptic pH in the brain. Altered activity of this enzyme may be the target of acetazolamide therapy.

A case of familial paroxysmal nonkinesigenic dyskinesia due to mutation of the PNKD gene in Chinese Mainland

BACKGROUND

Paroxysmal dyskinesia is a rare neurological disorder characterized by paroxysmal movement disorders. Paroxysmal movement disorders include kinesigenic choreoathetosis, nonkinesigenic choreoathetosis or dyskinesia (PNKD), exercise-induced choreoathetosis, and hypnogenic paroxysmal dystonia. There have been some sporadic reports of PNKD occurrences in Chinese Mainland, but none has been reported on familial PNKD. Proband and methods A 32 years old male admitted to the First Affiliated Hospital of Chinese PLA General Hospital, Beijing, China in 2009 with recurrent limb involuntary movements spanning over 30 years was diagnosed with PNKD. Family history was collected to identify if it was a case of familial or sporadic PNKD. Mutation and linkage analysis were performed to identify the pathogenic gene and the localization of the same.

RESULTS

There were five generations of 26 patients, out of which 3 of these patients died. Follow-up was conducted on 17 out of the 23 patients alive and 9 normal family members. The pedigree showed autosomal dominant inheritance, whom could be divided into light, moderate, and severe group according to clinical signs, spontaneous attack and response to drugs. All patients harbored c.20C>T (p.A7V) mutation in exon 1 of the PNKD/MR-1 gene. Preliminary linkage analyses using phenocopy rates of 0.0001 and 0.1 suggested that linkage signal localizes between D2S126 and D2S377. The functional consequence of the mutation in the disease pathogenesis is pending investigation. Conclusions We report the first case of familial paroxysmal non-kinesigenic dyskinesia (PNKD) in Chinese Mainland, which coincidentally is also the largest case of familial PNKD ever reported. This article is part of a Special Issue entitled Brain and Memory.