title: Genetic mapping of new DNA probes at Xq27 defines a strategy for DNA studies in the fragile X syndrome.
abstract: The fragile X syndrome is the most common cause of familial mental retardation and is characterized by a fragile site at the end of the long arm of the X chromosome. The unusual genetics and cytogenetics of this X-linked condition make genetic counseling difficult. DNA studies were of limited value in genetic counseling, because the nearest polymorphic DNA loci had recombination fractions of 12% or more with the fragile X mutation, FRAXA. Five polymorphic loci have recently been described in this region of the X chromosome. The positions of these loci in relation to FRAXA were defined in a genetic linkage study of 112 affected families. The five loci--DXS369, DXS297, DXS296, IDS, and DXS304--had recombination fractions of 4% or less with FRAXA. The closest locus, DXS296, was distal to FRAXA and had a recombination fraction of 2%. The polymorphisms at these loci can be detected in DNA enzymatically digested with a limited number of restriction endonucleases. A strategy for DNA studies which is based on three restriction endonucleases and on five probes will detect one or more of these polymorphisms in 94% of women. This strategy greatly increases the utility of DNA studies in providing genetic advice to families with the fragile X syndrome.
authors.affiliation: Department of Cytogenetics and Molecular Genetics, Adelaide Children's Hospital, Australia.
authors.forename: G K
authors.initials: GK
authors.lastname: Suthers
authors.forename: J C
authors.initials: JC
authors.lastname: Mulley
authors.forename: M A
authors.initials: MA
authors.lastname: Voelckel
authors.forename: N
authors.initials: N
authors.lastname: Dahl
authors.forename: M L
authors.initials: ML
authors.lastname: Väisänen
authors.forename: P
authors.initials: P
authors.lastname: Steinbach
authors.forename: I A
authors.initials: IA
authors.lastname: Glass
authors.forename: C E
authors.initials: CE
authors.lastname: Schwartz
authors.forename: B A
authors.initials: BA
authors.lastname: van Oost
authors.forename: S N
authors.initials: SN
authors.lastname: Thibodeau
mesh_terms: D002874:Chromosome Mapping; D004247:DNA / Q000032:analysis*; D015342:DNA Probes; D005600:Fragile X Syndrome / Q000175:diagnosis*; D008040:Genetic Linkage; D006801:Humans; D009154:Mutation; D010375:Pedigree; D012150:Polymorphism, Restriction Fragment Length; D011995:Recombination, Genetic; D014960:X Chromosome
chemical_list: D015342:DNA Probes; D004247:DNA