Genetic mapping of new DNA probes at Xq27 defines a strategy for DNA studies in the fragile X syndrome |
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| Authors: | G K Suthers J C Mulley M A Voelckel N Dahl M L Visnen P Steinbach I A Glass C E Schwartz B A van Oost S N Thibodeau N E Haites B A Oostra R Gin M Carballo C P Morris J J Hopwood and G R Sutherland |
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| Institution: | Department of Cytogenetics and Molecular Genetics, Adelaide Children's Hospital, Australia. |
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| 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. |
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