A ThirdLocusforAutosomal Dominant Cerebellar Ataxia TypeIMapstoChromosome14q24.3-qter: Evidence forthe Existence ofa Fourth Locus

Summary Theautosomal dominant cerebellar ataxias (ADCA) typeIarea group ofneurological disorders that are clinically andgenetically heterogeneous. Twogenesimplicated inthedisease, SCA1(spinal cerebellar ataxia 1) andSCA2, arealready localized. Wehavemapped athird locus tochromosome 14q24.3-qter, bylinkage analysis inanon-SCA1/non-SCA2 family andhaveconfirmed its existence ina second suchfamily. We suggest designating this new locus "SCA3." Combined analysis ofthetwofamilies restricted theSCA3locus toa 15-cM interval between markers D14S67andD14S81. ThegeneforMachado-Joseph disease (MJD), a clinically different formofADCAtypeI,hasbeenrecently assigned tochromosome 14q24.3-q32. Although theSCA3 locus iswithin theMJDregion, linkage analyses cannotyetdemonstrate whether they result frommutations of the same gene.Linkage toallthree loci (SCA1, SCA2,andSCA3) was excluded inanother family, which indicates theexistence ofafourth ADCAtypeIlocus.