| Description |
Paroxysmal nonkinesigenic dyskinesia (PNKD) is an autosomal-dominant disorder that belongs to a group of hyperkinetic movement disorders called the paroxysmal dyskinesias. PNKD is characterized by spontaneous paroxysmal attacks of any combination of dystonia, chorea, athetosis, and ballism, which are precipitated by alcohol, coffee, stress, and fatigue. Previous reports indicated that the PNKD locus was located on chromosome 2q, but the gene responsible for PNKD was not known. This dissertation describes the search and ultimate discovery of the gene responsible for PNKD. We performed PNKD locus fine-mapping, built a physical contig across the PNKD locus, and analyzed of disease haplotypes through PNKD kindreds in order to facilitate the screening process for the PNKD gene. Direct sequencing and denaturing high pressure liquid chromatography (dHPLC) were used for screening genes located within the PNKD region. We identified two missense mutations in a novel gene called Myofibrillogenesis Regulator 1 (MR-1), which caused PNKD in 50 affected individuals from eight PNKD kindreds. The mutations caused alanine-tovaline changes in the N-terminus of two MR-1 isoforms. The MR-1L isoform is specifically expressed in neurons and is localized to the cell membrane, while the MR-1S isoform is ubiquitously expressed and shows diffuse cytoplasmic and nuclear localization. The mRNA of the MR-1 mouse ortholog, brain protein 17 (BRP17), shows a wide expression pattern throughout the mouse central nervous system (CNS). The expression of MR-1/BRP17 in the cerebral cortex, cerebellum, spinal cord, and basal ganglia, implied that MR-1 plays an important role in maintaining the excitability of these essential parts of the motor system. Bioinformatic analysis reveals that the MR-1 gene is homologous to the hydroxyacylglutathione hydrolase (HAGH) gene. HAGH functions in a pathway to detoxify methylglyoxal, a compound present in coffee and alcoholic beverages and produced as a by-product of oxidative stress. Our results suggest a mechanism whereby alcohol, coffee, and stress may act as precipitants of attacks in PNKD. Since MR-1, unlike the genes known of cause other episodic disorders, is neither an ion channel nor an ion exchanger gene, it provides a new avenue for exploration into the pathophysiology of episodic phenomena like PNKD and perhaps epilepsy or migraine. |
