A female compound heterozygote (pre- and full mutation) for the CGG FMR1 expansion |
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Authors: | M Milà Sergi Castellví-Bel Ramon Giné Carlos Vazquez Cèlia Badenas Aurora Sánchez Xavier Estivill |
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Institution: | (1) Servei de Genètica, Hospital Clìnic, c/Villaroel 170, E-08036 Barcelona, Spain Tel.: +34-3-227-54-00; Fax: +34-3-227-54-54; e-mail montse@medicina.ub.es, ES;(2) Servicio de Genética, Hospital Materno Infantil, Las Palmas de Gran Canaria, Spain, ES |
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Abstract: | Fragile X syndrome is the most common cause of inherited mental retardation. The incidence has been estimated to be 1 in
1250 males and 1 in 2000 females. Molecular studies have shown that 95% of fragile X syndrome cases are caused by the expansion
of a CGG triplet in the FMR1 gene with hypermethylation of the adjacent CpG island. In spite of the high incidence of this
syndrome, a female with both FMR1 genes in the expanded form has never been reported. We present here a female from the Canary
Islands presenting mental retardation and attention problems. Molecular analysis has revealed that both of her FMR1 genes
have the CGG expansion, one with a premutation and the other with a full mutation. We have studied the CGG repeat in the FMR1
gene in 64 members of her family and detected 33 normal individuals, 14 carriers with the premutation (1 male and 13 females),
and 18 individuals with full mutations (8 males and 10 females). The index case illustrates that the possibility of both parents
being carriers of the fragile X syndrome premutation should be considered in consanguineous families or in small communities.
Received: 4 April 1996 / Revised: 3 May 1996 |
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