Objective-To repor the study of a multigenerational Swiss family with dopa-responsive dystonia (DRD).Methods-Clinical investigation was made of available family members, including historical and chart reviews. Subject examinations were video recorded. Genetic analysis included a genome-wide linkage study with microsatellite markers (STR), GTP cyclohydrolase I (GCH1) gene sequencing, and dosage analysis.Results-We evaluated 32 individuals, of whom 6 were clinically diagnosed with DRD, with childhood-onset progressive foot dystonia, later generalizing, followed by parkinsonism in the two older patients. The response to levodopa was very good. Two additional patients had late onset doparesponsive parkinsonism. Three other subjects had DRD symptoms on historical grounds. We found suggestive linkage to the previously reported DYT14 locus, which excluded GCH1. However, further study with more stringent criteria for disease status attribution showed linkage to a larger region, which included GCH1. No mutation was found in GCH1 by gene sequencing but dosage methods identified a novel heterozygous deletion of exons 3 to 6 of GCH1. The mutation was found in seven subjects. One of the patients with dystonia represented a phenocopy.Conclusions-This study rules out the previously reported DYT14 locus as a cause of disease, as a novel multiexonic deletion was identified in GCH1. This work highlights the necessity of an accurate clinical diagnosis in linkage studies as well as the need for appropriate allele frequencies, penetrance, and phenocopy estimates. Comprehensive sequencing and dosage analysis of known genes is recommended prior to genome-wide linkage analysis. Dopa-responsive dystonia (DRD) is a rare disorder characterized by childhood-onset fluctuating foot dystonia, which later generalizes and becomes associated with tremor and parkinsonism. 1-3 Response to small doses of levodopa is dramatic. In its classic form, also Although close to 100 mutations have been described in GCH1, 6 comprehensive screening fails to identify the responsible mutation in 40 to 50% of the families. 7 Recently, families have been described with heterozygous exonic deletions in GCH1, which were not detected by conventional screening techniques. 8-11In this study, we report more comprehensive clinical and genetic investigations of a multigenerational DRD family, in which a previous study had found linkage to a novel locus nominated DYT14 on chromosome 14q13, adjacent to the DYT5 locus. 12 Expanded data allowed us to exclude DYT14, and to identify a novel deletion in GCH1 as the disease-causing mutation in this family. METHODS Genealogy and clinical evaluationsInformation on the pedigree was collected by means of historical material, family records, and medical charts review, along with interviews with elderly family members.The project was approved by the local ethics committee. After signing an informed consent, subjects underwent a detailed videotaped neurologic evaluation. A clinical diagnosis of definite DRD was established in pa...