Identification ofnew DNA markers close to themyotonic dystrophy locus

Themostuseful markers fortheprenatal diagnosis ofmyotonic dystrophy (DM) areAPOC2 and CKM,bothofwhichmapproximal toDM.Inorder toproduce other markers useful forDM, wehave screened genomic DNA libraries constructed from cell line 20XP3542-1-4, whichcontains 20to30Mb ofhumanmaterial including APOC2 andCKM. Of 51humanclones identified, sevenmap to chromosome 17,fourtochromosome 8,andnineto chromosome 19,andtheremaining 31wereexcluded fromchromosome 19butnotlocalised further. Fouroftheclones fromchromosome 19mapdistal toCKM andtwooftheseclones (D19S62 and D19S63) areclosely linked toDM. Analysis ofa family inwhich acrossover between CKM andDM hasoccurred showsthatneither D19S62nor D19S63andDM haverecombined, suggesting thatD19S62andD19S63areeither closer toor flanking DM inrelation toCKM.Pulsed field gel analysis showedthatCKM,D19S62, andD19S63 maptoaregion ofatleast 1500kb. Myotonic dystrophy (DM)isthemostcommonadult formofmuscular dystrophy.' Itisanautosomal