The parental origin of the single X chromosome in Turner syndrome: lack of correlation with parental age or clinical phenotype.

We have used X- and Y-linked RFLPs to determine the origin of the single X chromosome in 25 live-born individuals with Turner syndrome. We determined that 18 individuals retained a maternal X (Xm) and that seven retained the paternal X (Xp). No occult mosaicism was detected. We found no differences in either maternal or paternal ages for the two groups. The ratio of maternal X to paternal X is just over 2:1, which is consistent with the expected proportion of meiotic or mitotic products, with equal loss at each step, given the nonviability of 45,Y. Six phenotypic or physiologic characteristics were assessed: (1) birth weight, (2) height percentile at time of testing, (3) presence of a webbed neck, (4) cardiovascular abnormalities, (5) renal abnormalities, and (6) thyroid autoimmunity. There were no significant differences in birth weights or heights between the girls who retained the maternal X or the paternal X. In addition, no differences between the groups could be appreciated in the incidence of the physical, anatomic, or physiologic parameters assessed.     

Cytogenetic and molecular analysis of sex-chromosome monosomy.

X chromosome- and Y chromosome-specific DNA probes were used to study different aspects of the genesis of sex-chromosome monosomy. Using X-linked RFLPs, we studied the parental origin of the single X chromosome in 35 spontaneously aborted and five live-born 45,X conceptions. We determined the origin in 35 cases; 28 had a maternal X (Xm) and seven had a paternal X (Xp). There was a correlation between parental origin and parental age, with the Xp category having a significantly reduced mean maternal age by comparison with the Xm group. Studies aimed at detecting mosaicism demonstrated the presence of a Y chromosome or a second X chromosome in three of 33 spontaneous abortions, a level of mosaicism much lower than that reported for live-born Turner syndrome individuals.     

Exclusively paternal X chromosomes in a girl with short stature

A 13 1/2 year-old girl with short stature and very few Turner stigmata revealed 45,X/46,XX mosaicism with 90%–100% 46,XX cells in three sequential blood lymphocyte cultures. Molecular investigation of the parental origin of her X chromosomes revealed homozygosity for paternal X markers and an absence of maternal markers. Luteinizing hormone response to growth hormone releasing hormone was increased. Impaired gonadal function and shortness of stature in this case could be a result of the mild mosaicism with a 45,X cell line and/or is a consequence of the paternal-only origin of her X chromosomes.     

Turner syndrome mosaicism: an unusual case with a de novo large dicentric marker chromosome: mos 45,X/46,X, ter rea(X;X)(p22.3;p22.3)

X/X translocations are quite rare in humans. The effect of this anomaly on the phenotype is variable and depends on the amount of deleted material and whether the chromosomes are joined by their long or short arms. We report an unusual case of Turner syndrome mosaicism in a 16-year-old girl, who was referred to our Institute for primary amenorrhoea associated with short stature. Endocrine evaluation revealed hypergonadotropic hypogonadism, which required a study of the karyotype. Cytogenetic analysis, performed on peripheral blood leucocytes, showed a mos 45,X/46,X,ter rea (X;X)(p22.3;p22.3) de novo karyotype. The prevalent cell line was 45,X (90% cells). A second cell line (10% cells) showed a very large marker chromosome, similar to a large metacentric chromosome. FISH (fluorescent in situ hybridisation) and molecular analysis revealed that the marker chromosome was dicentric and totally derived from the paternal X chromosome.     

Analysis of sex chromosome aneuploidy in sperm from fathers of Turner syndrome patients

Numerical sex chromosome abnormalities were analyzed in sperm from four fathers of Turner syndrome patients of paternal origin to determine whether there was an increased frequency of sex chromosome aneuploidy and to elucidate whether meiotic malsegregation mechanisms could be involved in the origin of Turner syndrome. Determination of the parental origin of the single X chromosome (maternal in all four cases) and exclusion of X and Y mosaicism were carried out by polymerase chain reaction amplification of five X chromosome polymorphisms and three Y chromosome segments. A total of 45,299 sperm nuclei from Turner fathers and 85,423 sperm nuclei from eight control donors was analyzed by three-color fluorescence in situ hybridization. The four patients showed a significant increase in the percentages of XY sperm (mean 0.22%; range 0.20% to 0.22%) compared with control donors (mean 0.11%; range 0.06% to 0.18%). These results suggest that the four individuals have an increased frequency of nondisjunctional errors in meiosis I, resulting in the production of an increased proportion of XY spermatozoa and of sperm lacking a sex chromosome. Received: 24 November 1998 / Accepted: 2 February 1999     

Coincident maternal meiotic nondisjunction of chromosomes X and 21 without evidence of autosomal aysnapsis

Summary A family in which the proband showed phenotypic signs of both the Turner and Down syndromes was studied cytogenetically and with restriction fragment length polymorphisms. The proband's karyotype was 46,X,+21, showing double aneuploidy without any signs of mosaicism. The single X and one chromosome 21 were of paternal origin while two chromosomes 21 were of maternal origin. The nondisjunction of chromosome 21 took place in maternal meiosis II. If it is assumed that the absence of mosaicism renders postzygotic mitotic loss of the X chromosome unlikely, then the X chromosome would have been lost in maternal meiosis I or II. Recombination had occurred between the nondisjoined chromosomes 21. We conclude that double nondisjunction took place in one parent and that asynapsis was not a prerequisite for the autosomal nondisjunction.     

del(X)(p22.1)/r(X)(p22.1q28) Dynamic mosaicism in a Turner syndrome patient

We report on a 16-year-old patient with Turner syndrome who presented a mos 46,X,del(X)(p22.1)[35]/45,X [19]/46,X,r(X)(p22.1q28)[6]GTG-band karyotype. The R-banding showed that the abnormal X-chromosome was inactive in all 61 cells analyzed. Fluorescence in situ hybridization with a Xp/Yp subtelomeric probe revealed that both abnormal chromosomes lacked the complementary sequences, a fact consistent with a terminal deletion. Besides, the molecular analysis of the human androgen receptor gene showed that the rearranged chromosome was paternal in origin. Since the deleted and the ring chromosomes had the same size and banding pattern, and because the former was the predominant cell line, it was inferred that the Xp- formed a ring in some cells apparently without further loss of genetic material. However, the reverse sequence and even a simultaneous origin due to a complex intrachromosomal exchange are also conceivable. The mild Turner syndrome phenotype is explained by the mosaicism and by the size of the deleted segment.     

Height correlation analysis between women with Turner syndrome, their sisters and parents

INTRODUCTION: The most frequent physical features associated with Turner syndrome is short stature. The main goal of the research was to estimate the height of women with Turner syndrome and to analyze the correlation between their height and their sisters and parents height. MATERIAL AND METHODS: The research was based on the 176 women with Turner syndrome (number of parents = 176; number of sisters = 122). The data was collected from 1995 to 2002 in Out-patient Clinic for Women with Turner's Syndrome in Bytom. RESULTS: Average height in the group of women non treated with growth hormone and anabolic drugs was 144.1 +/- 6.8 cm (n = 105), mothers average height: 162 +/- 5.3 cm, fathers average height: 172.4 +/- 6.1 cm, sisters: 164.9 +/- 5.2 cm (n = 79). The height of women with karyotype 45,X was slightly shorter: 143.1 +/- 6.9 cm, while the height of the family have remained unchanged. Contrary to all untreated women with Turner syndrome where the height was correlated with the mothers and fathers height (pearson's r = 0.32 and 0.34 respectively), sisters height was correlated mainly with fathers height (pearson's r = 0.47 and 0.34 respectively). In the group with karyotype 45,X patients' height was correlated mainly with mothers height (r = 0.55). In this group sisters height is correlated stronger with fathers' height (r = 0.45) than with mothers' height (r = 0.35). CONCLUSIONS: 1. The height of non treated women with Turner syndrome is correlated with both parents height while the height of sisters is correlated mainly with fathers. 2. The height of Turner syndrome women with karyotype 45,X is correlated with their mothers height.     

The late-replicating X chromosome in digynous mouse triploid embryos

Using BrdU-labeling and acridine orange staining, the behavior of X-chromosome replication was studied in 28 XXX and 19 XXY digynous mouse triploids. In some of these the paternal and maternal X chromosome could by cytologically distinguished. Such embryos were obtained by mating chromosomally normal females with males carrying Cattanach's X chromosome which contains an autosomal insertion that substantially increases the length of this chromosome. In the XXX triploids there were two distinct cell lines, one with two late-replicating X chromosomes, and the other with only one late-replicating X. The XXY triploids were also composed of two cell populations, one with a single late-replicating X and the other with no late replicating X chromosome. Assuming that the late-replicating X is genetically inactive, in both XXX and XXY triploids, cells from the embryonic region tended to have only one active X chromosome, whereas those from the extra-embryonic membranes tended to have two active X chromosomes. The single active X chromosome was either paternal or maternal in origin, but two active X chromosomes were overwhelmingly maternal in origin, suggesting paternal X-inactivation in extra-embryonic tissues.     

Concomitant Turner syndrome and hemophilia A in a female with an idic(X)(p11) heterozygous at locus DXS52.

A 46,X,idic(X)(p11) karyotype was found in a female affected by Turner syndrome and sporadic moderate hemophilia A. Restriction fragment length polymorphism analysis of the patients's DNA demonstrated that the idic(X) contained alleles from both maternal X chromosomes. Since the idic(X) appeared to be always inactivated, a de novo mutation of factor VIII in the normal paternal X chromosome is probably responsible for the patient's coagulation disorder.     

The proportion of cells with functional X disomy is associated with the severity of mental retardation in mosaic ring X Turner syndrome females

Turner syndrome females (45,X) do not have mental retardation (MR), whereas some mosaic ring X Turner syndrome females, with 45,X/46,X,r(X), have severe MR. The MR is believed to be caused by a failure of X chromosome inactivation (XCI) of the small ring X chromosome, which leads to functional X disomy (FXD), To explore this hypothesis, we examined the proportion of FXD cells in the peripheral blood of four ring X Turner syndrome females with various levels of MR, using two newly developed XCI assays based on DNA methylation of X-linked genes. As a result, the two patients with extremely severe MR showed complete FXD patterns, whereas the remaining two patients with relatively milder MR showed partial FXD patterns. These results indicate that the proportion of FXD cells may be associated with the severity of MR in mosaic ring X Turner syndrome females, although this association should be confirmed by examining brain cells during development. One of the cases with severe MR and a complete FXD pattern neither lacked the XIST gene nor had uniparental X isodisomy, and we discuss the mechanism of the failure of XCI in this case.     

X chromosome inactivation in carriers of Barth syndrome.

Barth syndrome (BTHS) is a rare X-linked recessive disorder characterized by cardiac and skeletal myopathy, neutropenia, and short stature. A gene for BTHS, G4.5, was recently cloned and encodes several novel proteins, named "tafazzins." Unique mutations have been found. No correlation between the location or type of mutation and the phenotype of BTHS has been found. Female carriers of BTHS seem to be healthy. This could be due to a selection against cells that have the mutant allele on the active X chromosome. We therefore analyzed X chromosome inactivation in 16 obligate carriers of BTHS, from six families, using PCR in the androgen-receptor locus. An extremely skewed X-inactivation pattern (>=95:5), not found in 148 female controls, was found in six carriers. The skewed pattern in two carriers from one family was confirmed in DNA from cultured fibroblasts. Five carriers from two families had a skewed pattern (80:20-<95:5), a pattern that was found in only 11 of 148 female controls. Of the 11 carriers with a skewed pattern, the parental origin of the inactive X chromosome was maternal in all seven cases for which this could be determined. In two families, carriers with an extremely skewed pattern and carriers with a random pattern were found. The skewed X inactivation in 11 of 16 carriers is probably the result of a selection against cells with the mutated gene on the active X chromosome. Since BTHS also shows great clinical variation within families, additional factors are likely to influence the expression of the phenotype. Such factors may also influence the selection mechanism in carriers.     

De novo DNA methylation independent establishment of maternal imprint on X chromosome in mouse oocytes

In female mouse embryos, the paternal X chromosome (Xp) is preferentially inactivated during preimplantation development and trophoblast differentiation. This imprinted X-chromosome inactivation (XCI) is partly due to an activating imprint on the maternal X chromosome (Xm), which is set during oocyte growth. However, the nature of this imprint is unknown. DNA methylation is one candidate, and therefore we examined whether disruptions of the two de novo DNA methyltransferases in growing oocytes affect imprinted XCI. We found that accumulation of histone H3 lysine-27 trimethylation, a hallmark of XCI, occurs normally on the Xp, and not on the Xm, in female blastocysts developed from the mutant oocytes. Furthermore, the allelic expression patterns of X-linked genes including Xist and Tsix were unchanged in preimplantation embryos and also in the trophoblast. These results show that a maternal disruption of the DNA methyltransferases has no effect on imprinted XCI and argue that de novo DNA methylation is dispensable for Xm imprinting. This underscores the difference between imprinted XCI and autosomal imprinting.     

Heterogeneous X inactivation in trophoblastic cells of human full-term female placentas

In female mammalian cells, one of the two X chromosomes is inactivated to compensate for gene-dose effects, which would be otherwise doubled compared with that in male cells. In somatic lineages in mice, the inactive X chromosome can be of either paternal or maternal origin, whereas the paternal X chromosome is specifically inactivated in placental tissue. In human somatic cells, X inactivation is mainly random, but both random and preferential paternal X inactivation have been reported in placental tissue. To shed more light on this issue, we used PCR to study the methylation status of the polymorphic androgen-receptor gene in full-term human female placentas. The sites investigated are specifically methylated on the inactive X chromosome. No methylation was found in microdissected stromal tissue, whether from placenta or umbilical cord. Of nine placentas for which two closely apposed samples were studied, X inactivation was preferentially maternal in three, was preferentially paternal in one, and was heterogeneous in the remaining five. Detailed investigation of two additional placentas demonstrated regions with balanced (1:1 ratio) preferentially maternal and preferentially paternal X inactivation. No differences in ratio were observed in samples microdissected to separate trophoblast and stromal tissues. We conclude that methylation of the androgen receptor in human full-term placenta is specific for trophoblastic cells and that the X chromosome can be of either paternal or maternal origin.     

Hunter disease (mucopolysaccharidosis type II) associated with unbalanced inactivation of the X chromosomes in a karyotypically normal girl.

The mechanism of profound generalized iduronate sulfatase (IDS) deficiency in a developmentally delayed female with clinical Hunter syndrome was studied. Methylation-sensitive RFLP analysis of DNA from peripheral blood lymphocytes from the patient, using MspI/HpaII digestion and probing with M27 beta, showed that the paternal allele was resistant to HpaII digestion (i.e., was methylated) while the maternal allele was digested (i.e., was hypomethylated), indicating marked imbalance of X-chromosome inactivation in peripheral blood lymphocytes of the patient. Similar studies on DNA from maternal lymphocytes showed random X-chromosome inactivation. Among a total of 40 independent maternal fibroblast clones isolated by dilution plating and analyzed for IDS activity, no IDS- clone was found. Somatic cell hybrid clones containing at least one active human X chromosome were produced by fusion of patient fibroblasts with Hprt- hamster fibroblasts (RJK88) and grown in HAT-ouabain medium. Methylation-sensitive RFLP analysis of DNA from the hybrids showed that of the 22 clones that retained the DXS255 locus (M27 beta), all contained the paternal allele in the methylated (active) form. No clone was isolated containing only the maternal X chromosome, and in no case was the maternal allele hypermethylated. We postulate from these studies that the patient has MPS II as a result of a mutation resulting in both the disruption of the IDS locus on her paternal X chromosome and unbalanced inactivation of the nonmutant maternal X chromosome.     

A case of female hemophilia with a 46,XXr karyotype studied with X-chromosome DNA probes

Summary A case of female hemophilia with a 46,XXr/45,X karyotype and signs of Turner syndrome, has been followed for the past 10 years. One of her brothers also has hemophilia A. A study with polymorphic DNA probes located in the Xq27-qter region has enabled us to demonstrate that the ring chromosome is of paternal origin and that the factor VIII gene region is deleted. The hemizygous state allowed expression of the hemophilia A mutation, present on the morphologically normal X chromosome, inherited from her carrier mother.     

Acrocentric chromosome disomy is increased in spermatozoa from fathers of Turner syndrome patients

The aim of the present study was to investigate whether there was an increase of aneuploidy in the sperm from fathers of Turner syndrome patients of paternal origin who, in a previous study, showed an elevated incidence of XY meiotic nondisjunction. Sperm disomy frequencies for chromosomes 4, 13, 18, 21 and 22 were assessed by fluorescence in situ hybridisation in four of these individuals. As a group, the Turner syndrome fathers showed a general increase in disomy frequencies for chromosomes 13, 21 and 22, with a statistically significant increase in disomy frequencies for chromosomes 13 and 22 in one of the fathers and for chromosome 21 in two of them. Data from a previous work carried out by us in two fathers of Down syndrome patients of paternal origin also revealed increased sperm disomy frequencies for chromosomes 13, 21 and 22. Pooled as one group, these six fathers of aneuploid offspring of paternal origin had a statistically significant increase in the frequency of nondisjunction for these chromosomes with respect to control individuals. Our findings indicate that there may be an association between fathering aneuploid offspring and increased frequencies of aneuploid spermatozoa. Such increases do not seem to be restricted to the chromosome pair responsible for the aneuploid offspring. Acrocentric chromosomes and other chromosome pairs that usually show only one chiasma during meiosis seem to be more susceptible to malsegregation.     

Molecular studies of parental origin and mosaicism in 45,X conceptuses

Summary The present report summarizes molecular studies of parental origin and sex chromosome mosaicism in forty-one 45,X conceptuses, consisting of 29 spontaneous abortions and 12 liveborn individuals with Turner syndrome. Our studies indicate that most 45,X conceptuses have a single, maternally derived X chromosome, regardless of whether the conceptus is liveborn or spontaneously aborted. In studies of mosaicism, our identification of X- and Y-chromosome mosaics among 45,X spontaneous abortions indicates that mosaicism does not ensure survival to term of 45,X fetuses. However, the incidence of sex chromosmome mosaicism is substantially higher in liveborn than in aborted 45,X conceptuses, indicating that the presence of a second cell line increases the likelihood of survival to term.     

The origin of 45,X males.

Maleness in association with the karyotype 45,X is a very rare and hitherto unexplained condition previously described in only four or five patients. This study was carried out to determine whether such males might actually possess Y-chromosomal material. Of the two 45,X males studied, one was found to be a low-grade mosaic with a 46,XY karyotype in less than 3% of fibroblasts; all lymphocytes karyotyped were 45,X. Fibroblast DNA from this individual was found to contain Y-specific repeated sequences in 1%-3% the amount observed in the father, consistent with mosaicism for a 46,XY cell line. No Y-specific repeated sequences were detected in the other patient, in whom all mitoses were 45,X. In neither patient were there detectable amounts of any of the single-copy Y-specific DNA sequences for which we tested. Studies of Xg blood groups and of X-linked restriction fragment length polymorphisms indicated that the single X chromosome was of maternal origin in both 45,X male probands. In contrast to the situation in XX males, we can exclude paternal X-Y interchange as the etiology in the cases described here. Our findings are compatible with mosaicism being the explanation of at least some "45,X" males.