Chromosome studies of four neurodegenerative diseases are described in current literature: Huntington disease cases in Finland show linkage disequilibrium of chromosome 4rflp haplotypes . Hereditary Motor and Sensory Neuropathy Type I shows linkage to the pericentromeric region of chromosome 17 . Friedreich’s ataxia gene has been assigned to chromosome 9q13-q21 . The dystonia gene in Ashkenazi Jewish population has been located on chromosome 9q32-34 . The same gene may be responsible for idiopathic torsion dystonia in non-Jewish kindred. Most familial forms of idiopathic torsion dystonia follow autosomal dominant transmission with reduced penetrance. The frequency in Ashkenazi Jewish population is 5-10 times greater than that in other groups.