* Objective: To describe characteristics of gene-negative patients with clinical features of Huntington's disease (HD), exploring likely etiologies.
*Background: When a direct gene test became definitive for diagnosis of HD, we discovered a number of patients in our clinics in Baltimore, MD, and Cambridge, UK, believed or suspected to have HD who did not have the triplet repeat expansion.
* Methods: Patients were examined using standardized instruments, and given full neurologic and psychiatric evaluations. Those negative for HD were tested for dentatorubro-pallidoluysian atrophy, SCA-1, SCA-3, SCA-2, SCA-6, and other conditions as indicated.
* Results: Of 15 patients, 7 received specific diagnoses or appear to be sporadic cases, 4 have a possible but uncertain relation to HD, and 4 have unknown familial progressive movement disorders.
* Conclusions: This last group of patients might be properly described as phenocopies of HD, some of which may be caused by unidentified triplet repeat expansions.