Dilemmas in counselling females with the fragile X syndrome.
The dilemmas in counselling a mildly retarded female with the fragile X syndrome and her retarded partner are presented. The fragile X syndrome is an X linked mental retardation disorder that affects males and, often less severely, females. Affected females have an increased risk of having affected offspring. The counselling of this couple was complicated by their impaired comprehension which subsequently impaired their thinking on the different options. The woman became pregnant and underwent CVS, which showed an affected male fetus. The pregnancy was terminated. Whether nondirective counselling for this couple was the appropriate method is discussed and the importance of a system oriented approach, through involving relatives, is stressed. (+info
Different targets for the fragile X-related proteins revealed by their distinct nuclear localizations.
Fragile X syndrome is caused by the absence of the fragile X mental retardation protein (FMRP). FMRP and its structural homologues FXR1P and FXR2P form a family of RNA-binding proteins (FXR proteins). The three proteins associate with polyribosomes as cytoplasmic mRNP particles. Here we show that small amounts of FMRP, FXR1P and FXR2P shuttle between cytoplasm and nucleus. Mutant FMRP of a severely affected fragile X patient (FMRPI304N) does not associate with polyribosomes and shuttles more frequently than normal FMRP, indicating that the association with polyribosomes regulates the shuttling process. Using leptomycin B we demonstrate that transport of the FXR proteins out of the nucleus is mediated by the export receptor exportin1. Finally, inactivation of the nuclear export signal in two FXR proteins shows that FMRP shuttles between cytoplasm and nucleoplasm, while FXR2P shuttles between cytoplasm and nucleolus. Therefore, molecular dissection of the shuttling routes used by the FXR proteins suggests that they transport different RNAs. (+info
Feasibility and acceptance of screening for fragile X mutations in low-risk pregnancies.
Fragile X syndrome is the second leading cause of mental retardation after Down syndrome. Most women carriers of the fragile X mutation are unaware of their condition. We critically evaluated whether screening pregnant women at low risk for FMR1 mutation would be feasible as a routine part of antenatal care in general practice. We also studied acceptance and attitudes to gene testing. From July 1995 until December 1996, a carrier test was offered at the Kuopio City Health Centre free of charge to all pregnant women in the first trimester following counselling given by midwives on fragile X syndrome. All women found to be carriers of FMR1 gene mutations underwent detailed genetic counselling and were offered prenatal testing. Attitudes towards the gene test were elicited by questionnaire. Most pregnant women (85%) elected to undertake the gene test. Six women were found to be carriers (a rate of 1 in 246), and all subsequently accepted prenatal testing. Three foetuses had a normal FMR1 gene, one had a large premutation, one a 'size mosaic' mutation pattern, and another a full mutation. This observational and interventional study demonstrates that antenatal screening provides an effective way of identifying carriers and incorporating prenatal testing into this process. (+info
Monozygotic twin brothers with the fragile X syndrome: different CGG repeats and different mental capacities.
Little is known about the mechanism of CGG instability and the time frame of instability early in embryonic development in the fragile X syndrome. Discordant monozygotic twin brothers with the fragile X syndrome could give us insight into the time frame of the instability. We describe monochorionic diamniotic twin brothers with the fragile X syndrome who had different CGG repeats and different mental capacities, whereas the normal mother had a premutation. The more retarded brother had a full mutation in all his cells and no FMR-1 protein expression in lymphocytes, whereas the less retarded brother had 50%/50% mosaicism for a premutation and full mutation and FMR-1 protein expression in 26% of his lymphocytes. The differences in repeat size could have arisen either before or after the time of splitting. The time of splitting in this type of twin is around day 6-7. Given the high percentage of mosaicism, we hypothesise that the instability started before the time of splitting at day 6-7. (+info
Fragile X premutation is a significant risk factor for premature ovarian failure: the International Collaborative POF in Fragile X study--preliminary data.
The preliminary results of an international collaborative study examining premature menopause in fragile X carriers are presented. A total of 760 women from fragile X families was surveyed about their fragile X carrier status and their menstrual and reproductive histories. Among the subjects, 395 carried a premutation, 128 carried a full mutation, and 237 were noncarriers. Sixty-three (16%) of the premutation carriers had experienced menopause prior to the age of 40 compared with none of the full mutation carriers and one (0.4%) of the controls. Based on these preliminary data, there is a significant association between fragile X premutation carrier status and premature menopause. (+info
Human werner syndrome DNA helicase unwinds tetrahelical structures of the fragile X syndrome repeat sequence d(CGG)n.
Formation of hairpin and tetrahelical structures by a d(CGG) trinucleotide repeat sequence is thought to cause expansion of this sequence and to engender fragile X syndrome. Here we show that human Werner syndrome DNA helicase (WRN), a member of the RecQ family of helicases, efficiently unwinds G'2 bimolecular tetraplex structures of d(CGG)7. Unwinding of d(CGG)7 by WRN requires hydrolyzable ATP and Mg2+ and is proportional to the amount of added helicase and to the time of incubation. The efficiencies of unwinding of G'2 d(CGG)7 tetraplex with 7 nucleotide-long single-stranded tails at their 3' or 5' ends are, respectively, 3.5- and 2-fold greater than that of double-stranded DNA. By contrast, WRN is unable to unwind a blunt-ended d(CGG)7 tetraplex, bimolecular tetraplex structures of a telomeric sequence 5'-d(TAGACATG(TTAGGG)2TTA)-3', or tetramolecular quadruplex forms of an IgG switch region sequence 5'-d(TACAGGGGAGCTGGGGTAGA)-3'. The ability of WRN to selectively unwind specific tetrahelices may reflect a specific role of this helicase in DNA metabolism. (+info
Serum concentrations of follicle stimulating hormone may predict premature ovarian failure in FRAXA premutation women.
It is now recognized that female carriers of fragile X premutations are at increased risk of premature ovarian failure. We have studied 51 premenopausal women from fragile X families, to determine whether premutation carriers have variations in the hormonal markers of menopause, compared to full mutations and controls. We found a significant increase in serum follicle stimulating hormone in premutation carriers, suggesting that as a group they will enter menopause before full mutation carriers and unaffected controls. These results have important implications for fertility in these women. (+info
Noninvasive test for fragile X syndrome, using hair root analysis.
Identification of the FMR1 gene and the repeat-amplification mechanism causing fragile X syndrome led to development of reliable DNA-based diagnostic methods, including Southern blot hybridization and PCR. Both methods are performed on DNA isolated from peripheral blood cells and measure the repeat size in FMR1. Using an immunocytochemical technique on blood smears, we recently developed a novel test for identification of patients with fragile X syndrome. This method, also called "antibody test," uses monoclonal antibodies against the FMR1 gene product (FMRP) and is based on absence of FMRP in patients' cells. Here we describe a new diagnostic test to identify male patients with fragile X syndrome, on the basis of lack of FMRP in their hair roots. Expression of FMRP in hair roots was studied by use of an FMRP-specific antibody test, and the percentage of FMRP-expressing hair roots in controls and in male fragile X patients was determined. Control individuals showed clear expression of FMRP in nearly every hair root, whereas male fragile X patients lacked expression of FMRP in almost all their hair roots. Mentally retarded female patients with a full mutation showed FMRP expression in only some of their hair roots (<55%), and no overlap with normal female controls was observed. The advantages of this test are (1) plucking of hair follicles does no appreciable harm to the mentally retarded patient, (2) hairs can be sent in a simple envelope to a diagnostic center, and (3) the result of the test is available within 5 h of plucking. In addition, this test enabled us to identify two fragile X patients who did not show the full mutation by analysis of DNA isolated from blood cells. (+info