Sex Chromosome Mosaicism Research Articles

Chromosome studies in patients with defective reproductive success.

The objective of this study was to evaluate the contribution of chromosomal anomalies to decreased fertility in humans. In order to investigate the aetiology of infertility in our population and to assess the karyotype in a group of infertile couples and individuals with fertility problems, 782 persons (259 couples, 158 male and 106 female) with different clinical diagnoses of sterility and infertility were analysed cytogenetically. The overall frequency of major chromosomal aberration was 13.1% (103/783), which suggests that fertility or sterility problems in this population are due to chromosomal aberrations. Couples experiencing repeated spontaneous abortions, having malformed children or having sterility problems had chromosomal abnormalities in 18.0% (47/259 couples) of the population studied, and constituted chromosomal disorders occured in couples seeking IVF and ICSI with prevalence of 22.2% (8/38 couples), especially minor mosaicism of sex chromosomes in the female partners. The prevalence of chromosome abnormalities in infertile men was 17.7% (28/158), and in subfertile females, it was 26.4% (28/106). These results could indicate an increased tendency to miotic sex chromosome non-disjuction in humans.

Analysis of sex chromosome aneuploidy in 41 patients with Turner syndrome: a study of 'hidden' mosaicism.

We performed a genetic study of sex chromosome mosaicism in 41 Turner syndrome patients. The investigation was carried out in four phases: cytogenetics (G-banding), FISH, PCR for SRY in all 41 cases, and sequencing of the SRY gene in the 2 patients with the Y chromosome. The application of classical alpha-satellite probes (CEP-X and CEP-Y), painting probes (WCP-X and WCP-Y) and also XIST, DXZ4 and two subchromosomal painting libraries (SCPL 116 and SCPL102) covering the short and the long arm of the X chromosome, respectively, allowed us to find new mosaic cell lines (mosaicism) in 37 out of 41 patients; only 4 patients were defined as 45,X non-mosaic. The most frequent hidden mosaic was 45,X/46,XX in 32% of the cases; the presence of isochromosomes comprised 25% and markers 5%. The patients who had been previously diagnosed as mosaics displayed a higher complexity in their karyotypes due to the presence of new cell lines. The Y chromosome and the SRY gene were present in blood and ovarian tissue in 2 patients with karyotypes 45,X/46,XY and 45,X/46,X,idic(Ynf). In both patients, the sequencing of the SRY gene confirmed a nucleotide sequence identical to that of a control male. Our results support the hypothesis of 'the necessity of mosaicism for survival', and thus, a mitotic origin for this syndrome.

Cyto 2000 – A Collaborative study for the evaluation of blood chromosome mosaicism

The implications of chromosomal mosaicism have plagued cytogenetics laboratories over the past 40 years. Although this is a frequent phenomena in the clinical cytogenetics laboratory and often misunderstood, there has been little work examining this phenomena. In order to understand better the clinical impact of mosaicism we have undertaken a multi-laboratory survey of mosaicism. We have surveyed 29 laboratories in which over 151,000 stimulated peripheral blood specimens have been studied in a 7-9 year period. A total of 2109 mosaic cases have been identified in these laboratories. Evaluation of this data initially revealed that three different methods of establishing mosaicism was implemented in these labs, although 65% of the labs used the definition of 2 or more cells with trisomy or structural rearrangements and 3 or more cells with monosomy for a specific chromosome. Additionally, 65% of the labs believed that only one culture was needed to establish mosaicism. Among the labs, the range of mosaicism varied between 0.38% and 2.97%, with an overall frequency of 1.39%. Results of the types of mosaicism, revealed that sex chromosomal mosaicism was significantly more common than autosomal mosaicism (64% vs 36%). Overall, half of the sex chromosome mosaicism involved 45,X mosaicism; 45,X/numerical mosaicism was most common (30%) and 45,X/structural mosaicism was slightly less common (20%). Among the autosomal mosaicism, the majority either involved trisomy (mostly chromosome 21) or mosaicism of an accessory marker/ring chromosome. It was interesting to note that 9% of the total mosaic specimens (and 25% of the autosomal cases) involved an autosomal structural mosaic. This is a higher frequency than initially expected.This survey encompasses the largest group yet studied to explain and understand mosaicism. Results from these studies show that: (1) laboratories do not use uniform criteria to establish mosaicism, and three different criteria were noted in this study; (2) the overall frequency of mosaicism was approximately 1.39%, but there was significant differences between labs; (3) sex chromosome mosaicism was most commonly detected, with the majority involving a 45,X cell line; and (4) autosomal structural mosaicism was more frequent than expected and may have a greater impact than expected. Additional studies are in progress, specifically examining the minimum number of cells needed to establish mosaicism and the effect of ascertainment on the findings. The accumulation of this data will provide a better understanding of the phenomena of mosaicism.

Recurrence of triploidy in a woman with low level 45,X mosaicism

Triploidy (69 chromosomes) occurs in 1 to 3% of recognized pregnancies typically resulting in first trimester spontaneous abortion. The recurrence risk after one affected pregnancy is 1-1.5%. Triploidy can be diandric or digynic in origin. Diandric triploids result from dispermy or fertilization from a diploid sperm. Diandric triploids result in a partial hydatidiform mole. Digynic triploids may be due to a complete nondisjunctional event during oogenesis, retention of a polar body or fertilization of an ovulated primary oocyte. Digynic triploids may survive to the second trimester and develop as a growth retarded fetus with a small placenta. We report a woman with four first trimester spontaneous abortions of which three were triploid. The first miscarriage was not karyotyped, the second showed 69.XXX, the third 69.XXY and the fourth 69,XXX. Parent of origin studies were not performed, so it is unclear whether the triploid conceptions were diandric or digynic in origin. The proband also has a normal son. Chromosomal analysis on the proband showed 45,X[3], 46,XX[27]. Although nondisjunction is reported among offspring of Turner mosaics, we are not aware of any other reports of recurrent triploidy associated with low level sex chromosome mosaicism in the mother. The triploidy may be directly correlated with Turner mosaicism or may represent a random association.

Type and frequency of chromosome aberrations in 781 couples undergoing intracytoplasmic sperm injection.

Cytogenetic investigations were performed in 781 couples prior to intracytoplasmic sperm injection (ICSI) because of severe male infertility or fertilization failures in previous in-vitro fertilization attempts. Out of these 1562 patients, 1012 had a normal karyotype without any aberrations (64.8%), 204 patients had an abnormal karyotypes (13.1%). These chromosome aberrations included constitutional aberrations (4.4%), fragile sites of autosomes (3.0%), low level mosaicism of sex chromosomes (4.0%) and secondary structural chromosome aberrations (4.2%). Combinations of different types of abnormalities were stated. Another 346 patients (22.1%) showed single cell aberrations; the significance of these is unclear at the moment. Constitutional chromosome aberrations were detected in 69 patients. The following chromosome aberrations were observed: 35 sex chromosomal aberrations (comprising hyperploidies of X or Y chromosomes, mosaicisms and derivative X and Y chromosomes), 34 autosomal aberrations including 14 reciprocal translocations, five Robertsonian translocations, six inversions, one marker chromosome, one trisomy 18 mosaicism and seven other structural aberrations. Three autosomal regions showed fragile sites: 6q13 in 2.9% of the patients, 17p12 and 10q24 in 0.05% each. In conclusion, our data show that a high number of infertile couples in an ICSI programme are affected by chromosome aberrations which occur in both sexes. It is suggested that a chromosomal analysis should be performed on both partners before ICSI treatment is initiated.

Prenatal interphase detection by FISH of a sex chromosome mosaicism when cytogenetics reports a pseudomosaicism

We report the detection of a sex chromosome mosaicism (XY/XXY/XYY) by prenatal interphase FISH (fluorescence in situ hybridization) originally identified as a pseudomosaicism involving 47,XXY cells present in a routine 46,XY cytogenetic analysis. After a fetal demise, interphase FISH identified the sex chromosome mosaicism in all tissues examined while cytogenetic analysis revealed only a normal male cell line. After prolonged exposure to colcemid, cytogenetic analysis identified the 47,XXY cell line. This confirmed the presence of the mosaicism and suggested that the abnormal cell line(s) may have been growth disadvantaged. This in turn may have accounted for the intra-uterine fetal demise. The identification by FISH and the role of growth-disadvantaged cell lines may provide a unique insight into chromosomally normal fetal demises.

Prenatal interphase detection by FISH of a sex chromosome mosaicism when cytogenetics reports a pseudomosaicism

Prenatal interphase detection by FISH of a sex chromosome mosaicism when cytogenetics reports a pseudomosaicism

Chromosomal aberrations in couples undergoing intracytoplasmic sperm injection: influence on implantation and ongoing pregnancy rates

Objective: To determine the incidence of chromosomal aberrations in couples undergoing intracytoplasmic sperm injection (ICSI) and their influence on subsequent implantation and ongoing pregnancy rates. Design: Prospective study. Setting: Fertility center. Patient(s): Candidates for ICSI. Intervention(s): Chromosomes were trypsin-banded in 2,280 patients. In all cases, 10 metaphases were karyotyped. Sex chromosome analysis was performed in 10 additional metaphases. When apparent chromosomal aberrations were detected, 100 metaphases were analyzed. Main Outcome Measure(s): Implantation and ongoing pregnancy rates in couples with a chromosomal disorder. Results: A chromosomal abnormality was demonstrated in 7.2% of all couples. Among the male partners, 4.48% had aberrations. Autosomal aberrations were present in 2.96%, and numerical or structural sex chromosome abnormalities were found in 1.52%. Among the female partners, numerical or structural abnormalities were documented in 9.79%. Only 2.32% of the female partners had autosomal structural abnormalities. Numerical or structural anomalies involving sex chromosomes were found in 7.47%. Implantation rates of 9.4% and 16.3% per embryo were observed in female partners with sex chromosome mosaicism and autosomal aberrations, respectively. In male partners, the respective rates were 3.8% and 23.1%. Conclusion(s): The incidence of chromosomal disorders in couples seeking ICSI treatment is considerable, especially minor mosaicism (<10%) of sex chromosomes in the female partners. Preliminary data indicate a low implantation rate in couples with minor mosaicism of sex chromosomes.

Application of fluorescent in situ hybridization with X and Y chromosome specific probes to buccal smear analysis.

Conventional X- and Y-chromatin and fluorescent in situ hybridization (FISH) analysis based on X- and Y-chromosome specific probes were conducted from buccal smear, on 15 normal males, 15 normal females, and 9 cases suspected of sex chromosome anomalies. The proportion of X- and Y-chromatin in normal females and males was 12% +/- 3% and 51.5% +/- 4.9%, respectively, by the conventional X- and Y-chromatin procedure. The CEP-X/Y analysis by FISH for the same specimens provided a proportion of 98.8% +/- 0.7% cells with XX signals in the normal females and 99.8% +/- 0.4% cells with XY signals in the normal males. The FISH method was superior to the conventional procedure in nine cases suspected of sex chromosome anomalies, including one case of mosaicism. The results of CEP-X/Y will sometimes be false; it will not detect structural anomalies of sex chromosomes, and it is not intended to detect low level mosaicism. However, the test is useful for rapid screening of sex chromosome aneuploidy at a fraction of the cost for chromosome analysis. The FISH test is also appropriate to detect tissue specific sex chromosome mosaicism, especially if it is relatively high. This FISH test is best used as an adjunct to chromosome analysis whenever possible.

Early second-trimester determination of fetal gender by ultrasound.

Ultrasound identification assists in determining chorionicity in twins, in the interpretation of sex chromosome mosaicism and aneuploidy and in sex-linked conditions presenting after 14 weeks. This study addresses the frequency and accuracy of gender identification in a series of consecutive patients presenting for amniocentesis for genetic indications. Amniocentesis was performed at 14-20 weeks in 843 fetuses over a 5-year period. Ultrasound prediction of fetal gender was documented in 93.3% (770/843). The overall accuracy of diagnosis of fetal gender was 99.3% (765/770). Errors in diagnosis of gender were more likely to occur in the assessment of the female fetus. Such errors in diagnosis may be minimized by combining both tangential/transverse and sagittal views of the fetal perineum.

Dicentric Y Chromosome Without Evidence of Mosaicism in an Azoospermic Male

A phenotypically male of dicentric Y chromosome with no evidence of sex chromosomal mosaicism is reported. Staining of fluorescence in situ hybridization using Y chromosome centromere-specific DNA probe showed the presence of two bright fluorescent spots in Y chromosome. Testicular histology revealed maturation arrest at the stage of primary spermatocyte. It is suggested that structural anomaly of the Y chromosome is related to the disturbance of spermatogenesis.

Sex Diagnosis and Sex Chromosomal Mosaicism in Normal Human Preimplantation Embryos.

The sex of human preimplantation embryos was determined by fluorescent in-situ hybridization (FISH), and the reliability of this method was evaluated. Preimplantation sex determination by FISH was performed with blastomeres dissociated from pre- implantation embryos with 2 pronuclei in the 2-8 cell stage that were obtained by intracytoplasmic sperm injection (ICSI). Dual color FISH analysis was performed with DXZ1 and DYZ1, X and Y chromosome-specific probes, respectively. The detection sensitivity of DXZ1 and DYZ1 was evaluated with interphase nuclei of human lymphocytes obtained from normal males and females. The signal detection rate in these nuclei was 92.0% (460/500) in the males and 89.4% (447/500) in the females. The fixation rate of single blastomeres determined by FISH was 88.7% (86/97). The sex determined by FISH was the same in all blastomeres within the embryo in 20 (80%) of 25 embryos; 11 embryos were determined to be males and 9 to be females. The other 5 embryos (20%) showed sex chromosomal mosaicism. When the results in 2 blastomeres are normal and consistent, the probability that the remaining part of the embryo was mosaic was 12% (3/25). When the sex of the entire embryo is determined by biopsy of 2 blastomeres instead of 1 blastomere, mosaicism can therefore be excluded with a reliability of 88%, and more accurate diagnosis is possible.

Is the 15-in situ clone protocol necessary to detect amniotic fluid mosaicism?

OBJECTIVE: Our purpose was to evaluate the 15-clone analysis for detecting amniotic fluid mosaicism by the in situ method. STUDY DESIGN: A 10-year review was performed of all amniotic fluid mosaicism cases at two institutions using the in situ method exclusively, with sequential clonal analysis to determine the first and second clone in which the abnormal cell line occurred. RESULTS: Of the 28,497 amniotic fluid samples, 73 met criteria for amniotic fluid mosaicism by in situ method (0.26%). There were 54 cases (0.19%) with potential clinical significance (23 autosome and 31 sex chromosome mosaicism), 49 of the 54 cases (89%) were detected in the first six clones, including 22 of 23 involving autosomes and 27 of 31 involving sex chromosomes. In one of the six cases detected after clone 6 ( 46, XX 47, XX , + 21 ) the mosaic cell line was present in 20% of the clones analyzed and was followed by a voluntary termination of the pregnancy. In the other five cases amniotic fluid mosaicism was present in <20% of the clones; these included one case of 46, XX 47, XX + mar (15% amniotic fluid mosaicism, voluntary termination of pregnancy), two cases of 45, X 46, XY (10% to 12% amniotic fluid mosaicism, both normal at birth), and two cases of 45, X 46, XX (8% amniotic fluid mosaicism, lost to follow-up; 12% amniotic fluid mosaicism, voluntary termination of pregnancy). By limiting the analysis to six clones, ∼20% of analysis time could be saved per case, but one autosomal amniotic fluid mosaicism case per 10,000 samples could potentially be missed. CONCLUSION: Reducing the number of clones analyzed by in situ method could result in increased efficiency, decreased costs, and minimal loss of sensitivity.

Turner's syndrome with sex chromosome mosaicism

The increased risk of gonadal neoplasia in cases of Turner's syndrome with sex chromosome mosaicism and the presence of Y chromosome material emphasises the need for a diligent search and removal of the streak gonads. One such case is reported here.

Interphase cytogenetics on paraffin-embedded sections of ovary for detection of genomic constitution in a patient with Turner's syndrome and chromosomal mosaicism

The difficulty of detecting sex chromosome mosaicism cytogenetically hinders the finding of an acceptable explanation for phenotypic-genotypic discrepancy amongst those patients. Fluorescence in situ hybridization (FISH) permits the genomic identification of patients with mosaic karyotypes in interphase nuclei by utilising an X chromosome-specific DNA probe (interphase cytogenetics). We evaluated the efficiency of interphase cytogenetics in the detection of the genomic constitution of the ovary from a patient with Turner's syndrome having mosaicism (46,XX/45,X0) previously established by blood lymphocyte karyotyping. We used a biotin-labelled alphoid repetitive sequence, pBAMX5, specific for the centromeric region of the human X chromosome. Although examination of ovarian sections and blood lymphocytes by FISH showed the presence of both 46,XX and 45,X0 cell lines, the genomic constitution of the germ cells/oocytes in ovarian primordial follicles was shown to be normal (46,XX). Our results (1) show the high applicability of interphase cytogenetics on paraffin sections, (2) indicate the possibility of genomic screening of different tissues that are otherwise not amenable to routine cytogenetic investigation and (3) offer a reliable methodological approach to defining accurate by the percentage of abnormal karyotypes in mosaicism of different organs and non-dividing tissues.

The role of cordocentesis in assessment of mosaicism found in amniotic fluid cell culture.

Chromosomal mosaicism presents one of the most difficult problems in prenatal cytogenetic diagnosis, requiring the differentiation of true mosaicism from pseudomosaicism. To overcome associated problems and to prevent termination of normal pregnancies, we investigated 23 pregnancies in which true mosaicism has been found in amniotic fluid cell culture. A fetal blood sample was obtained by cordocentesis for rapid karyotyping, and meticulous sonographic examinations were carried out for detecting fetal abnormalities. The 23 cases in which mosaicisms were found in amniocytes involved five cases with sex chromosomal abnormalities, twelve with autosomal trisomy, four with autosomal structural defects, one with a supernumerary marker and one with tetraploidy. The karyotype from fetal leukocytes confirmed the diagnosis of mosaicism in only three out of 23 cases. These three included: two autosomal trisomies (47,XY + 13/47,XY + 21 and 46,XY/47,XY + 21) and one sex chromosome mosaicism (45,X/46,XY). These were all selected for elective termination of pregnancies by the parents' request. Post abortion karyotype re-confirmed previous karyotype. The other twenty lymphocyte karyotypes were normal, and of these, 19 patients gave birth at term, and one delivered prematurely due to premature rupture of membranes. All 20 born infants were found normal by both neonatal examination and re-karyotypes. We conclude that finding of mosaicism in amniotic fluid culture requires further investigation. Furthermore, in the presence of amniotic fluid cell true mosaicism and normal karyotype in fetal blood, continuation of the pregnancy is safe and to be recommended.

Cytomorphological results and dysplastic features as prognostic factors in 41 cases with acute myeloid leukemia (AML) and translocation

Abnormalities involving sex chromosomes account for approximately 0.5% of live births. The phenotypes of individuals with mosaic cell lines having structural aberrations of the X and Y chromosomes are variable and hard to accurately predict. Phenotypes associated with sex chromosome mosaicism range from Turner syndrome to males with infertility, and often present with ambiguous genitalia. Previous studies of individuals with an 45,X/46,X,idic(Y)(p11) karyotype suggest that the presence of both cell lines should result from an intermediate, 46,XY cell line. Here we report a 2.5 year old female with phenotypic features of Turner syndrome with an isodicentric Y chromosome and a cell line with a deleted Y with a final karyotype of 45,X/46,X,idic(Y)(p11.31)/46,X,del(Y)(p11.31). Fluorescence in situ hybridization (FISH) mapping of the Y chromosome breakpoint revealed very low percentages of the deleted Y cells, but suggested a potential mechanism for the formation of the isodicentric Y chromosome. To our knowledge, the 46,X,del(Y) intermediate cell line in our patient has not been previously reported in individuals with mosaic sex chromosome structural abnormalities.

Chromosome studies in in-vitro fertilization patients.

Human fertility problems may be due to chromosomal aberrations in one or both partners. In couples asking for in-vitro fertilization (IVF) the question arises as to whether chromosomal analysis is necessary. We analysed the karyotypes of 72 couples attending our clinic for IVF. Normal chromosomes were found in 131 individuals. One male was found to be a carrier of a Robertsonian translocation t(14q;21q), a second male had a reciprocal translocation t(2;4)(q14;p15) and 11 females exhibited sex chromosome mosaicism. A single cell aberration was demonstrated in 26% (38/144) of all individuals studied. These results clearly show that chromosomal analysis should be performed in couples asking for IVF.

Fragile site X chromosomes in mentally retarded boys.

The fragile X syndrome is a common X-linked mental retardation and autism, affecting females as well as males. The fragile site X chromosomes were studied in a series of 153 mentally retarded boys of unknown etiology to determine the frequency of fragile X syndrome, and to assess the feasibility of making a clinical diagnosis of the fragile X syndrome in young boys before cytogenetic results were known. The 10 boys (6.4%) were positive for fra (X) (q27). The phenotype of fra (X) (q27) positive patients were typical except one who also had sex chromosomal mosaicism. There were three pairs of siblings among the fra (X) (q27) positive patients. Frequency of expression of the fragile site was in 10 to 47 per cent of cells. In addition, 19 boys showed a previously unsuspected chromosomal abnormality. The frequency of the fragile X syndrome in the present study is not significantly different from those in Caucasians and Japanese population. The fragile X syndrome can be recognized by noting key aspects of family history as well as the clinical features in mentally retarded boys.

Prognosis of prenatally diagnosed children with sex chromosome aneuploidy.

Sex chromosome aneuploidy (SCA) occurs in about 1/250 amniocenteses, and the significance of the long-term prognosis of fetuses with SCA is of concern to prospective parents and health care providers. Longitudinal studies in an unselected group of newborn infants with SCA diagnosed postnatally have refuted allegations of mental retardation but have documented an increased risk for developmental problems. Of the 530 phone consultations with parents faced with a prenatal diagnosis of SCA, 68% continued the pregnancy. Twenty of the oldest subsequently born children (now 7-14 years old) were available for follow-up. In this small sample and age group, the propositi are progressing developmentally at a rate comparable to their sibs and are doing better at school and in peer relations than the SCA group diagnosed postnatally. Only 2 have documented IQs as low as 90. The documented IQs of the remainder, none of whom are sex chromosome mosaics, are all over 110. The parent population in this prenatally diagnosed group is unique and different from that of the postnatally diagnosed group in that over 85% of them are college graduates, often professionals, and upper socioeconomic individuals. The developmental competence of this SCA sample may be attributable to the supportive environment provided by these families, all of whom made a conscious decision to continue the pregnancy.