We will study paroxysmal dystonic choreoathetosis (PDC), an inherited disorder characterized by prolonged attacks of involuntary movements that occur spontaneously and often following caffeine or alcohol consumption. The cause of PDC is unknown and treatments are unsatisfactory. We propose that PDC is due to a mutation in an ion channel gene; or in a gene encoding a factor that interacts with or regulates ion channels in the CNS. This prediction is based on the fact that PDC is a paroxysmal disorder and the observation that ion channel gene mutations are responsible for thirteen other paroxysmal neurologic disorders. We will identify and analyze the PDC gene. We discovered the PDC locus on chr. 2q33-35, reduced this locus to 2.7 cM; created a physical map of this region; and identified and analyzed candidate genes at this locus. The PDC locus spans 2.4 Mb and has been >99% sequenced. 23 genes are known to be mapped to this locus. We completed the coding sequence analysis of eight of these genes. We used computer analysis of the PDC contig sequence to predict the presence of transcribed sequences; and then performed RT-PCR to determine which predicted genes were transcribed in the brain. This analysis indicates that 47 predicted genes are expressed in the brain. With automated DNA sequencing, we can analyze the coding sequence (approximtely 200,000 bp combined) of all known genes and predicted genes expressed in the brain within 18 months. To be thorough, we will determine the remaining 1% of DNA sequence of the PDC contig; and use other gene identification methods as needed. In parallel with candidate gene analysis, we will further reduce the PDC locus (and thus decrease the number of candidate genes) by a) determining if there are shared haplotypes between our five PDC kindreds; b) studying additional individuals in these kindreds; c) using single nucleotide polymorphism analysis to fine map the locus interval; and d) studying additional PDC kindreds (two more PDC kindreds were recently identified). If disease-specific coding sequence mutations are not identified in any PDC candidate gene, we will consider the possibility that the mutation involves gene regulatory elements; and analyze steady-state mRNA abundance and size of PDC candidate genes in lymphocyte mRNA (postmortem brain material as a source of mRNA is not available). After identifying the PDC gene, we will analyze the function of this gene by determining a) its tissue specific pattern of gene expression; b) its intracellular distribution; c) the proteins with which it interacts; and d) the consequences of introducing disease-specific PDC gene mutations in cultured cells and laboratory mice (gene knock-out and transgenic experiments). We are experienced with each of these methods. Identifying the PDC gene and understanding the molecular basis of PDC will help elucidate the causes of other movement disorders such as kinesigenic dyskinesia, neuroleptic induced tardive dyskinesia, and idiopathic dystonia; and provide insight into the physiology of alcohol and caffeine, which typically induce PDC attacks.
| Rainier, Shirley; Bui, Melanie; Mark, Erin et al. (2008) Neuropathy target esterase gene mutations cause motor neuron disease. Am J Hum Genet 82:780-5 |
