Fertility with deletion Xq25: report of three cases; possible exceptions for critical region hypothesis

Genes governing premature ovarian failure

Premature ovarian failure (POF) is unexplained amenorrhoea (>6 months), increased FSH (>20 IU/l) and LH occurring before 40 years. Several genes are reported as having significance in POF, including genes governing regulation of the hypothalamic-pituitary-ovarian axis, but their role in ovarian physiology is not known. Deletions or translocations in Xq arm have been found to be associated with POF, assuming presence of ovarian-related genes but ovary-related function of these genes is unclear. Several researchers have suggested specific loci on Xq critical region, POF1 and POF2 and genes DIA, FMR1 and FMR2. The understanding of ovarian physiology, its regulation and genes involved is important to explain the causes of POF. Some genes coordinate development of germ cell to primordial stage, e.g. GDF9, BMP15 and NGF, while others regulate development of further stages, such as FSH and LH. Mutation in these genes may lead to female infertility and are likely to be candidate genes for POF. Recently, association between blepharophimosis-ptosis-epicanthus inversus syndrome type 1 and POF has emerged as a possibility. Galactosaemia is also shown to be important in POF due to toxic effects of accumulated galactose or downstream products. Thus, understanding the role of several genes can be used for the appropriate genetic diagnosis, research and in the clinical practice of POF.

Prenatal diagnosis of a familial Xq deletion in a female fetus: a case report

X chromosome deletion is an infrequent finding in prenatal diagnosis and presents a difficult counseling challenge when it occurs. We present a case of a familial X chromosome long arm deletion discovered in a routine amniocentesis and subsequently in the mother. The pregnancy resulted in the birth of a normal girl, and X chromosome inactivation skewing was demonstrated in both mother and daughter. Xq deletion phenotypes and counseling issues are reviewed.

Ovarian differentiation and gonadal failure

Ovarian failure can result from several different genetic mechanisms-X chromosomal abnormalities, autosomal recessive genes causing various types of XX gonadal dysgenesis, and autosomal dominant genes. The number and precise location of loci on the X are still under investigation, but it is clear that, in aggregate, these genes are responsible for ovarian maintenance, given that monosomy X shows germ cells that undergo accelerated atresia. Despite recent hypotheses, at present there is no evidence for a gene directing primary ovarian differentiation; this process may be constitutive. Phenotypic/karyotypic correlation and limited molecular confirmation have long shown that proximal Xp and proximal Xq contain regions of the most importance to ovarian maintenance. Terminal deletions at Xp11 result in 50% primary amenorrhea and 50% premature ovarian failure or fertility. Deletions at Xq13 usually produce primary amenorrhea. Terminal deletions nearer the telomeres on either Xp of Xq bring about premature ovarian failure more often than complete ovarian failure. The X-linked zinc finger gene (ZFX) and diaphanous 2 Drosophila homologue (DIAPH2) are the only candidate genes for ovarian maintenance that map to the X chromosome. Additional, as yet unidentified, genes along the X chromosome must be involved. The search for these genes in humans is hampered by the lack of candidate genes that map to the X chromosome, the scarcity of patients with fortuitous autosomal translocations, and small pedigrees, which hinder mapping of the loci. In addition, difficulties with human germ cell research also make it challenging to dissect genes important to ovarian development. Autosomal genes also are involved in ovarian differentiation and gonadal failure. Follicle-stimulating hormone receptor and ataxia telangiectasia are examples of autosomal genes known to cause human ovarian failure. Transgenic mouse models point to many other candidate autosomal genes, and sequencing of the human homologues in affected women should lead to the discovery of new genes responsible for human ovarian failure. Identification, functional analysis, and mapping of novel genes specifically expressed in the ovary of mice and women eventually should lead to fruitful dissection of essential genes in mammalian ovarian development and maintenance.

Molecular and cytogenetic studies of X inactivation in a patient with 46,X,del(X)(q22)

We report on a phenotypically normal girl with a deletion of the distal long arm of one X chromosome at Xq22, and spontaneous pubertal development including menarche. This suggests that the distal long arm of the X chromosome is not crucial for ovarian development. Cytogenetic and polymerase chain reaction (PCR) amplification methods both showed preferential inactivation of the deleted X chromosome. The PCR-based assay has the additional advantage of identifying the paternal origin of the deleted X chromosome.

Deletions of Xq and growth deficit: a review

A critical review of the literature disclosed 44 cases with a 46,X,Xq- karyotype without apparent mosaicism. Of these, 17 were of normal height (compared to the respective population), 11 had a height of over 1 SD below the mean, and 16 had a height of over 2 SD below the mean with breakpoints between Xq13 and Xq25. Since patients of normal height occurred with breakpoints as proximal as Xq13 we conclude that there is no major "growth gene" on Xq distal to q13. The most likely explanation for the variable phenotypic effect of Xq- is to assume that growth gene(s) in Xp or proximal Xq are inactivated on such a chromosome with some variability similar to the variable spreading of X inactivation seen in some X-autosome translocations.