Molecular biology of Turner's syndrome

Functional and regulatory aspects of oxidative stress response in X monosomy

The partial/complete loss of one X chromosome in a human female leads to Turner syndrome (TS). TS individuals display a range of phenotypes including short stature, osteoporosis, ovarian malfunction, diabetes, and thyroid dysfunction. Epigenetic factors and regulatory networks are distinctly different in X monosomy (45, X). In a lifetime, an individual is exposed to a variety of stress conditions. To study whether X monosomy cells display a differential response upon exposure to mild stress as compared to normal 46, XX cells and whether this may contribute to various co-morbidities in aneuploid individuals, we have carried out a transcriptomic analysis of human fibroblasts 45, X and 46, XX after exposure to mild oxidative stress. Under these conditions, over 350 transcripts were seen to be differentially expressed in 45, X and 46, XX cells. Pathways associated with oxidative stress were differentially expressed highlighting the differential regulation of genes and associated phenotypes. It could be seen that X monosomy cells are more susceptible to oxidative stress as compared to normal cells and have altered molecular pathways both in normal conditions and also upon exposure to mild oxidative stress. To explore this aspect in detail, we have mapped the expressions of transcription factors (TFs) in 45, X and 46, XX cells. The network of transcription activating factors is differentially regulated in 45, X and 46, XX cells under stress exposure. It is tempting to speculate that the altered ability of 45, X (Turner) cells to respond to stress may play a significant role in the physiological function and altered phenotypes in Turner syndrome.

Turner's syndrome in dermatology

Turner's syndrome (TS) is a common genetic disorder of girls and women, for which the defining clinical triad is short stature, impaired sexual development, and infertility. Although classically known as monosomy X, genetic heterogeneity is frequent in TS, with mosaicism conferring a survival advantage. Several genetic loci have been implicated in TS including the short stature homeobox gene. TS effects many organs, with cutaneous stigmata providing critical clues for early detection of TS. The presence of lymphedema and its cutaneous sequelae are predictive of other systemic disorders, such as cardiac disease. Although an increased number of benign nevi have been reported in TS, the decreased melanoma rate in this population suggests some protective factor is active. Keloids were thought to be prevalent in TS, but recent data suggest otherwise. Autoimmune diseases are common in TS, with a possible increased prevalence of alopecia areata and vitiligo. The following review discusses new insights into the genetics and pathogenesis of this complex disorder, summarizes the major systemic effects, and reviews skin manifestations of TS and their implications.

Gonadoblastoma in Turner syndrome patients with nonmosaic 45,X karyotype and Y chromosome sequences

Turner syndrome (TS) is a disorder caused by partial or complete X-chromosome monosomy. Studies in TS patients with different karyotypes have demonstrated the presence of Y-chromosome-derived sequences (4-61%). Early detection of Y-chromosome sequences in TS is of great importance because of the high risk of gonadal tumor development. We investigated the presence of Y-chromosome sequences in TS patients with a 45,X karyotype. One hundred seven unrelated 45,X Mexican TS patients recruited between 1992 and 2003 were included. Y-chromosome-derived sequences were found by polymerase chain reaction in 10 (9.3%) patients. Six subjects underwent gonadectomy and in one of them a gonadoblastoma was found; another developed a gonadoblastoma with dysgerminoma. Because of the high proportion (33%) of gonadal tumors in patients with Y-chromosome sequences found among our patients of mestizo origin, adequate counseling regarding a gonadectomy should be given.

Molecular breakpoint analysis and relevance of variable mosaicism in a woman with short stature, primary amenorrhea, unilateral gonadoblastoma, and a 46,X,del(Y)(q11)/45,X karyotype

We report on a 30-year-old woman with short stature, completely female external genitalia, primary amenorrhea, bilateral streak gonads, unilateral gonadoblastoma, and a 46,X,del(Y)(q11)/45,X karyotype. Variable levels of mosaicism were found in blood and cultivated fibroblasts from both the skin and ovaries, with the percentage of the 45,X lineage never exceeding 33%. Fluorescence in situ hybridization (FISH) was performed with alpha satellite centromere region probes of the X and Y chromosomes (DXZ1 and DXZ3) as well as with the unique-sequence, locus-specific, sex-determining region of the Y chromosome gene (SRY) and the DXZ1 probes. Each signal was noted for DXZ1 on the X chromosome and for the Y probes on the marker chromosome. Molecular investigations with a panel of PCR markers spread over the whole Y chromosome indicated a deletion breakpoint between sY 78 (interval 4) and sY 151 (interval 5F). No mutation of the high mobility group-box (HMG-box) of the SRY gene could be found following sequence analysis. The phenotype/genotype correlation demonstrates the broad phenotypic range of low-level 45,X mosaicism with the resultant short stature and external female phenotype, despite the presence of SRY in a high proportion of cells in various tissues.

Molecular genetics of Turner syndrome: correlation with clinical phenotype and response to growth hormone therapy

To correlate the origin of the retained X in Turner syndrome with phenotype, pre-treatment height and response to recombinant human growth hormone (rhGH) therapy, systematic clinical assessment and molecular studies were carried out in 33 Greek children with Turner syndrome and their parents including 18 children with 45,X and 15 with X-mosaicism. Microsatellite markers on X chromosomes (DXS101 and DXS337) revealed that the intact X was paternal (Xp) in 15/30 and maternal (Xm) in 15/30 children, while 3/33 families were non-informative. No significant relationship was found between parental origin of the retained X and birth weight/length/gestational age, blepharoptosis, pterygium colli, webbed neck, low hairline, abnormal ears, lymphoedema, short 4th metacarpal, shield chest, widely spaced nipples, cubitus valgus, pigmented naevi, streak gonads, and cardiovascular/renal anomalies. With regard to the children's pre-treatment height, there was a significant correlation with maternal height and target height in both Xm and Xp groups. No differences were found between Xm and Xp groups and the improvement of growth velocity (GV) during the first and second year of rhGH administration, while for both groups GV significantly improved with rhGH by the end of the first and the second year. To our knowledge, this is the first attempt to correlate the parental origin of Turner syndrome with the response to rhGH therapy.

Y-chromosome identification by PCR and gonadal histopathology in Turner's syndrome without overt Y-mosaicism

OBJECTIVE

The frequency of gonadoblastoma is high in patients with Turner's syndrome bearing cells with Y or partial Y-chromosome. About 60% of patients with Turner's syndrome have a 45,X karyotype. In 30% of them a Y-sequence is disclosed by DNA analysis. To identify patients at risk of developing gonadoblastoma, a PCR based assay with SRY, ZFY and DYZ3 specific primers was carried out to detect different Y-sequences in the DNA of peripheral lymphocytes from patients with Turner's syndrome.

DESIGN AND PATIENTS

Peripheral blood karyotypes from 36 patients with Turner's syndrome were studied. Patients with proven Y-chromosomal material were excluded. Genomic DNA was extracted from peripheral blood. SRY and ZFY genes and DYZ3 repetion of Y-chromosome were amplified by PCR. Patients with clinical signs of hyperandrogenism or with positive Y-sequences by PCR underwent gonadectomy. The gonadal tissues were examined for Y-sequences using PCR, morphology and immunohistochemical study.

MEASUREMENTS

Turner's syndrome and signs of hyperandrogenism were evaluated both clinically and through laboratory tests. Haematoxylin and eosin staining was employed in gonadal morphology studies. The presence of testosterone was detected by immunohistochemistry using a monoclonal antibody.

RESULTS

Two patients who had Y-positive blood samples and three hyperandrogenic (2 hirsutes, 1 virilized) Y-negatives underwent gonadectomy. PCR was carried out on their gonadal tissue. The tissue from the two patients without hyperandrogenism was Y-positive. The gonadal tissue from the three hyperandrogenics was Y-negative. Gonadal morphology disclosed hilus cell hyperplasia in the 3 hyperandrogenic Y-negatives and in one Y-positive patient; stromal luteoma and hyperthecosis in the virilized patient, cystadenofibroma in one hirsute patient and gonadoblastoma in one Y-positive. Testosterone was detected immunohistochemically in the hilus cell hyperplasia, stromal luteoma and hyperthecosis found in the hyperandrogenic patients.

CONCLUSIONS

The molecular study was sensitive and useful in the evaluation of patients at risk of developing gonadoblastoma. Other nontumour, gonadotrophin-dependent and Y-independent mechanisms which deserve the same medical approach may be involved in the genesis of hyperandrogenic signs in Turner's syndrome.