Paracentric inversion X(q21.2q24) associated with mental retardation in males and normal ovarian function in females

[From pathological diagnosis to ovulation induction. The case of ovarian insufficiency]

The incidence of premature ovarian failure (POF) is around 1 to 3%. This pathology occurs in young women, who often wish to become pregnant. Theoretically, two mechanisms could be involved: initial follicle depletion and follicle dysfunction. However, in some cases, mixed mechanisms are involved. Initially, PFO was considered irreversible. In fact, signs of intermittent ovarian function in normal karyotypically women have been described, but predicting the probability of spontaneous remission in a specific woman is impossible. Therefore, various treatments for ovulation induction have been proposed to these patients. Most of the pregnancies occur after hormone replacement therapy. The action of this treatment is unclear and the cause-and-effect relation has not been proven by prospective, randomized studies. The benefit of suppressing endogen gonadotropins by GnRH agonists is not proven either. Estrogen supplementation and high-dose gonadotropin ovarian stimulation protocols have been proposed. Even so, this therapy cannot be recommended because of the lack of controlled studies. Finally, numerous case reports have described the return of ovarian function after using immunosuppressive therapies. The lack of particular criteria for the diagnosis of autoimmune mechanisms have lead to treat heterogeneous groups of patients. No randomized controlled studies with immunologic monitorage have been performed that could establish the success of this therapy. Therefore, in order to find effective treatments, basic pathophysiologic mechanisms must be better understood. For those women who want to become pregnant, the lack of prospective, randomized studies cannot lead to formal conclusions. Depending on the patients' age and history, it appears reasonable to attempt a corrective therapy based on defined etiology, before entering in a donor oocyte program.

Characterisation of an inverted X chromosome (p11.2q21.3) associated with mental retardation using FISH

We report on a patient with a pericentric inversion of the X chromosome, 46,Y,inv(X) (p11.2q21.3), who was referred for cytogenetic analysis because of mild mental retardation, short stature, prepubescent macro-orchidism, and submucous cleft palate. The same chromosomal abnormality was found in the proband's mother. The inverted X chromosome was late replicating in all the mother's lymphocytes studied, indicative of a likely unbalanced inversion. We show, by fluorescence in situ hybridisation (FISH) using a panel of ordered yeast artificial chromosome (YAC) clones, that the Xp breakpoint is localised in Xp11.23 between DXS146 and DXS255 and that the Xq breakpoint is assigned to the X-Y homologous region in Xq21.3. YACs crossing the Xp and Xq breakpoints have been identified. One of these two breakpoints could be linked to the mental retardation in this patient as many non-specific mental retardation (MRX) loci have previously been located in the pericentromeric region of the X chromosome. Morever, the elucidation at the molecular level of this rearrangement will also indicate if cleft palate or prepubescent macro-orchidism, or both, in this boy are related to one of the two X breakpoints.

Localization of two X-linked mental retardation (XLMR) genes to Xp: MRX37 gene at Xp22.31-p22.32 and a putative MRX gene on Xp22.11-p22.2

MRX genes of 2 families with X-linked mental retardation (XLMR) were localized by linkage analysis. In family A, the gene was mapped to Xp22.31-p22.32, with significant LOD scores to various Xp22 markers within a distance of 6 Mb between DXS1223 and DXS1224. The MRX gene of this family was designated MRX37. In a mentally retarded female who is a carrier of the MRX37 gene, a random pattern of X inactivation was demonstrated. In family B, a positive LOD score, although not significant (< + 2), was found with the marker DXS1202 at Xp22.11-p22.2.

Linkage analysis in three families with nonspecific X-linked mental retardation

Nonspecific X-linked mental retardation (XLMR) is a common disorder. The number of genes involved in this condition is not known, but it is estimated to be more than 10. We present a clinical and linkage study on 3 families with XLMR. All families were analyzed using highly polymorphic markers covering the X chromosome; screening for the fragile X mutation was negative. The first family (MRX 36) consisted of 1 female and 4 male patients in 3 generations and 7 healthy individuals. Considering the female as an expressing heterozygous carrier, a maximum LOD score of 3.41 was reached in region Xp21.2-Xp22.1. Considering her phenotype to be unknown, a LODmax of 1.97 was reached in the same region. The second family consisted of 5 affected and 6 healthy males with mild to borderline mental retardation. Linkage analysis using an X-linked recessive model with full penetrance and no phenocopies excluded linkage over almost the entire X chromosome. Using alternative models, including an affecteds-only analysis, a LODmax of 1.49 was found in region Xq24-28. The third family, consisting of 4 male patients with moderate mental retardation in 1 generation yielded a LODmax of 0.9 in region Xp22.13-11.3. However, even in this small pedigree, exclusion mapping was able to exclude very large parts of the X chromosome and in this way identify a likely candidate region.

Localisation of two candidate genes for mental retardation using a YAC physical map of the Xq21.1-21.2 subbands

Genetic studies in families with X linked mental retardation have suggested the location of several MR genes in the human q21 region. Since the establishment of cloned resources is an essential step towards the cloning of genes involved in inherited diseases, we built a yeast artificial chromosome (YAC) contig and an STS map of this part of the X chromosome. The contig, which extends from PGK1 in Xq13.3 to DXS1002 in Xq21.2, consists of 30 YACs mapped with 21 markers and spans about 6 Mb. The YAC contig was used as a framework to localise several previously known genes and CEPH/Genethon polymorphic markers, as well as to construct a physical map of the region surrounding one of these genes. We recently localised a presumed MR locus to the region flanked by DXS233 (proximal) and CHM (distal). In the present work, the zinc finger gene, ZNF6, has been shown to lie within this region and to be highly expressed in brain, making it a good candidate MR gene. Similarly the VDAC1 gene has been mapped between DXS986 and DXS72 and its candidate gene status for the Allan-Herndon-Dudley syndrome is discussed.

Localisation of a new gene for non-specific mental retardation to Xq22-q26 (MRX35)

Non-specific mental retardation (MR) is a condition in which MR appears to be the only consistent manifestation. The X linked form (MRX) is genetically heterogeneous. We report clinical, cytogenetic, and linkage data on a family with X linked non-specific MR. Two point and multi-point linkage analysis with 18 polymorphic markers, covering the entire chromosome, showed close linkage to DXS1001 and DXS425 with a maximal lod score of 2.41 at 0% recombination. DXS178 and the gene for hypoxanthine phosphoribosyl-transferase (HPRT), located in Xq22 and Xq26 respectively, flank the mutation. All other chromosomal regions could be excluded with odds of at least 100:1. To our knowledge there is currently no other non-specific MR gene mapped to this region. Therefore, the gene causing MR in this family can be considered to be a new, independent MRX locus (MRX35).