Del Xq23 in a mosaic Turner female: molecular and cytogenetic studies.

We report a Turner patient aged 22 years with a 45,X/46,X,del(X)(q23) karyotype. Late replication studies showed preferential inactivation of the deleted X chromosome; FISH studies with a probe for total human telomeres showed hybridisation signal in the telomeres on both the normal and the deleted X chromosomes. Microsatellite analysis in the proposita and her family permitted us to conclude to the maternal origin of the deleted X chromosome, and to detect using the marker DXS1106 (Xq22) a probable meiotic recombination event above the breakage point suggesting that the deletion occurred underneath this point.The mild Turner stigmata may be explained by the 45,X cell line, and the gonadal dysgenesis probably by a partial deletion of the gonadal dysgenesis region Xq13-q23 (excluding Xq22).     

A case of Turner's syndrome with hyperthyroidism

A female patient with classical gonadal dysgenesis associated with Graves' disease is reported. The karyotype was mosaicism of 45,X/46,X,i(Xq). The relationship among Graves' disease, Hashimoto's thyroiditis and Turner's syndrome is discussed along with a review of the reported cases.     

The critical region on the human Xq

Summary Adult female carriers of balanced X; autosome translocations (118 cases) and of balanced X inversions (31 cases) have been collected from the literature. Forty-five of the 118 translocation carriers in whom the break was in the critical region (Xq13–q22, Xq22–q26, separated by a narrow region within Xq22) showed gonadal dysgenesis. Seven of the 31 inversion carriers in whom the break was in the same region also had gonadal dysgenesis, whereas the remaining 24 were normal in this respect. The critical region consists mainly of Q-bright material, and is the fifth brightest segment in the human genome. The region contains relatively few genes. It is possible that meiotic crossing-over, rarely, if ever, takes place in it. The critical region may therefore consist of two supergenes whose integrity must be maintained to allow normal ovarian development. The effect exerted by this region differs from other known position effects, in that it is independent of the break-point within the region and of the chromosome bands to which the broken ends are attached. One possible mechanism causing this effect might be a change in the replication order of the chromosome bands, which, in turn, might affect their function.     

A possible exception to the critical region hypothesis.

Cytogenetic studies were done on a 5-year-old female with multiple congenital anomalies and mental retardation, revealing an unbalanced X/11 translocation. Her mother and phenotypically normal sister carry the balanced form of the translocation, while her brother has a normal 46,XY karyotype. Banding studies showed the breakpoints to be Xq22 and 11q13. These are remarkable for the following reasons: (1) the X breakpoint is within the critical region of the X chromosome, yet the balanced carrier does not manifest gonadal dysgenesis; and (2) the proband was trisomic for most of the long arm of chromosome 11. Late-replication studies of cells from the two balanced carriers showed inactivation of the normal X.     

The similarity of phenotypic effects caused by Xp and Xq deletions in the human female: a hypothesis

Summary We have collected from the literature adult nonmosaic women with the following aberrant X chromosomes: Xp- (52), Xq- (67), idic(Xp-)(10), idic(Xq-)(9), and interstitial deletions (12). Lack of Xp, and especially Xcen-Xp11 (b region), may cause full-blown Turner syndrome. However, individual Turner symptoms, including gonadal dysgenesis, otherwise seem to be randomly distributed with respect to the different Xp and Xq deletions, although breakpoints distal to Xq25 do not give rise to any phenotypic anomalies except in a few cases of secondary amenorrhea or premature menopause. Of the carriers of an Xp- or Xq- chromosome, 65% and 93%, respectively, suffer from ovarian dysgenesis, whereas all idic(Xp-) and idic(Xq-) chromosomes cause primary or secondary amenorrhea. Xq deletions do not induce specific symptoms different from those caused by Xp deletions. Lack of the tip of Xp has led in 46/52 cases to short stature, but 43% of the Xq- carriers are also short. To explain these observations, we propose the following hypothesis. Since deletions of truly inactivated regions do not seem to cause any symptoms, we assume that the b region (Xcen-p11) always stays active in a normal inactive X, but is inactivated in deleted X chromosomes, especially in Xq- chromosomes. In some cases, inactivation may spread to the tip of Xp; this would explain the apparently variable behavior of the Xg and STS genes, and the short stature of some Xq- carriers. Full chromosome pairing seems to be a prerequisite for the viability of oocytes and thus for gonadal development. Deleted X chromosomes necessarily leave a portion of the normal X unpaired and isodicentrics probably interfere with pairing, resulting in atresia of oocytes. The role played by the critical region (Xq13–q24) in ovarian development is still unclear.     

Recombinant chromosome as a result of pericentric inversion of X chromosome

Summary A structural X chromosome abnormality was found in the karyotype of a tall patient with gonadal dysgenesis and with no extragenital anomalies. Based on her mother's karyotype, which showed a pericentric inversion of the X chromosome: 46,X,inv(X)(p22q24), as well as from G and R banding, we concluded that the abnormal X chromosome of our patient was a recombinant chromosome that had originated as a result of one crossing over in the inversion loop during gametogenesis in her mother. The recombinant X chromosome had a partial deletion of Xq and a partial duplication of Xp: 46,X,rec(X),dup p,inv(X)(p22q24). After BUDR incorporation, the abnormal X chromosome of the patient and that of her mother showed a late replication. The karyotype-phenotype correlation and the nonrandom inactivation of the inverted X chromosome in the mother are discussed.     

De novo duplication xq22-q23 in a girl with short stature and gonadal dysgenesis

A female of 20 years of age with short stature, gonadal dysgenesis and Turner stigmata with a de novo dup Xq22-q23 was studied. The maternal cytogenetic study was normal. This case represents the smallest Xq duplication in an abnormal female. We discuss the possibility of a maternal imprinting.     

Turner's syndrome--correlation between karyotype and phenotype

Turner's syndrome is defined as a congenital disease determining by quantitative and/or structural aberrations of one from two X chromosomes with frequent presence of mosaicism. Clinically it is characterized by growth and body proportion abnormalities, gonadal dysgenesis resulting in sexual infantilism, primary amenorrhoea, infertility, characteristic stigmata, anomalies of heart, renal and bones and the presence of some diseases like Hashimoto thyroiditis with hypothyroidism, diabetes mellitus type 2, osteoporosis, hypertension. Turner's syndrome occurs in 1:2000 to 1:2500 female livebirth. The most frequent X chromosome aberrations in patients with phenotype of Turner syndrome are as follows: X monosomy - 45,X; mosaicism (50-75%), including 45,X/46,XX (10-15%), 45,X/46,XY (2-6%), 45,X/46,X,i(Xq), 45,X/46,X,del(Xp), 45,X/46,XX/47,XXX; aberration of X structure: total or partial deletion of short arm of X chromosome (46,X,del(Xp)) isochromosom of long arm of X chromosome (46,X,(i(Xq)), ring chromosome (46, X,r(X)), marker chromosome (46,X+m). Searching of X chromosome and mapping and sequencing of genes located at this chromosome (such as SHOX, ODG2, VSPA, SOX 3) have made possible to look for linkage between phenotypes and adequate genes or regions of X chromosome. In this paper current data concerning correlation between phenotype and karyotype in patients with TS have been presented.     

Molecular definition of Xq common-deleted region in patients affected by premature ovarian failure

High-resolution cytogenetic analysis of a large number of women with premature ovarian failure (POF) identified six patients carrying different Xq chromosome rearrangements. The patients (one familial and five sporadic cases) were negative for Turner's stigmata and experienced a variable onset of menopause. Microsatellite analysis and fluorescent in situ hybridization (FISH) were used to define the origin and precise extension of the Xq anomalies. All of the patients had a Xq chromosome deletion as the common chromosomal abnormality, which was the only event in three cases and was associated with partial Xp or 9p trisomies in the remaining three. Two of the Xq chromosome deletions were terminal with breakpoints at Xq26.2 and Xq21.2, and one interstitial with breakpoints at Xq23 and Xq28. In all three cases, the del(X)s retained Xp and Xq specific telomeric sequences. One patient carries a psu dic(X) with the deletion at Xq22.2 or Xq22.3; the other two [carrying (X;X) and (X;9) unbalanced translocations, respectively] showed terminal deletions with the breakpoint at Xq22 within the DIAPH2 gene. Furthermore, the rearranged X chromosomes were almost totally inactivated, and the extent of the Xq deletions did not correlate with the timing of POF. In agreement with previous results, these findings suggest that the deletion of a restricted Xq region may be responsible for the POF phenotype. Our analysis indicates that this region extends from approximately Xq26.2 (between markers DXS8074 and HIGMI) to Xq28 (between markers DXS 1113 and ALD) and covers approximately 22 Mb of DNA. These data may provide a starting point for the identification of the gene(s) responsible for ovarian development and folliculogenesis.     

The human inactivated X chromosome folds in early metaphase,prometaphase, and prophase

Summary The inactivated X chromosome has a site of unusually frequent folding in region Xq1, whereas a fold in Xq1 is uncommon on the active X. We investigated the pattern of X chromosome folding in high-resolution GTG- and RBG-stained preparations from four women. In early metaphase cells, slightly more than 50% of late-replicating Xs folded at Xq1Xq21, compared with about 6% of early replicating Xs. The late-replicating X folded in about 80% of prometaphase cells; the early, in only about 14% of these cells. And the latereplicating X folded in 19 of 20 prophase cells. Occasionally, one X had an omega-shaped loop or apparent physical connection between Xq13 and Xq21.1. It is possible that a segment of Xq1 never completely uncoils and may help to provide continuity for the Barr body from one interphase to the next.     

Deletion (X)(q26.1-->q28) in a proband and her mother: molecular characterization and phenotypic-karyotypic deductions.

During a routine prenatal diagnosis we detected a female fetus with an apparent terminal deletion of an X chromosome with a karyotype 46,X,del(X)(q25); the mother, who later underwent premature ovarian failure, had the same Xq deletion. To further delineate this familial X deletion and to determine whether the deletion was truly terminal or, rather, interstitial (retaining a portion of the terminal Xq28), we used a combination of fluorescence in situ hybridization (FISH) and Southern analyses. RFLP analyses and dosage estimation by densitometry were performed with a panel of nine probes (DXS3, DXS17, DXS11, DXS42, DXS86, DXS144E, DXS105, DXS304, and DXS52) that span the region Xq21 to subtelomeric Xq28. We detected a deletion involving the five probes spanning Xq26-Xq28. FISH with a cosmid probe (CLH 128) that defined Xq28 provided further evidence of a deletion in that region. Analysis with the X chromosome-specific cocktail probes spanning Xpter-qter showed hybridization signal all along the abnormal X, excluding the possibility of a cryptic translocation. However, sequential FISH with the X alpha-satellite probe DXZ1 and a probe for total human telomeres showed the presence of telomeres on both the normal and deleted X chromosomes. From the molecular and FISH analyses we interpret the deletion in this family as 46,X,del(X) (pter-->q26::qter). In light of previous phenotypic-karyotypic correlations, it can be deduced that this region contains a locus responsible for ovarian maintenance.     

Prenatal and postnatal characterization of a de novo Xq22.1 terminal deletion

We present a case of a de novo Xq22.1 chromosomal terminal deletion discovered prenatally by conventional cytogenetics. The pregnancy resulted in the birth of a normal girl. Preferential inactivation of the abnormal X was demonstrated postnatally. Fluorescence in situ hybridization (FISH) demonstrated a terminal Xq deletion spanning Xq22.1 -->qter. An X painting probe ruled out a translocation. The deleted X chromosome was determined to be of paternal origin. The girl is now 4 years old with normal physical and psychomotor development. X chromosomal deletions are infrequent findings in prenatal diagnosis and present a difficult counseling challenge when they occur. Prenatal X-inactivation studies provide an opportunity for more informative genetic counseling when a de novo X chromosome deletion is detected.     

Cell division and sister chromatid exchanges in 45,X/46,X,i(Xq) mosaicism

Summary The kinetics of cell division and sister chromatid exchanges were studied in PHA-stimulated short-term cultivations of peripheral blood by means of the BUDR/FPG technique in controls and in five patients with 45,X/46,X,i(Xq) mosaicism. No significant differences in the length of the cell cycle were observed between 45,X/46,X,i(Xq) and control 46,XX cells. The number of SCE on late i(Xq) was only nonsignificantly elevated (0.6 per i(Xq)) against the value expected on the basis of its relative length.     

Structural aberrations of the X chromosome in man

Summary Among 209 patients with Shereshevsky-Turner syndrome, 69 women with structural aberrations of X chromosome were detected: 46,X, i(Xq)-11; 45,X/46,X,i(Xq)-24; 45,X/46,X,r(X)-14; 45,X/46,X,f(X or Y)-10; 45,X/46,X,del(Xq)-4; 45,X/46,X,del(Xp)-2; 45,X/46,X,idic(X)-2; 46,X,idic(X)-1; and 46,X,t(X,2)-1. All the patients with structural abnormalities of X chromosome were short in stature, but in no group was it as low on the average as in 45,X cases. Somatic signs were noticed in all structural changes of X, but they were less frequent and less pronounced. In some patients with r(X) and i(Xq), spontaneous menstrual bleeding and breast development was found.The structurally abnormal X chromosome appears to be functionally inactive, the phenotype of patients with structural rearrangements being close to the phenotype of patients with X monosomy. At the same time, the abnormal X might have certain effects in early embryogenesis which mitigated the further development of the Shereshevsky-Turner syndrome.     

Repeated DNA sequences in the distal long arm of the human X chromosome

Summary Two DNA probes from within a single large insert from a recombinant phage-DNA library that was constructed from flow-sorted chromosomes enriched for the human X chromosome were shown to hybridize with repeated X-specific and autosomal DNA sequences. The X-chromosomal repeated sequences were assigned to the distal long arm of the X chromosome by both hybrid mapping and in situ hybridization. Fine mapping places these repeats in a region of Xq28 between DX13 (DXS15, in distal Xq28) and factor VIII (F8C, in proximal Xq28). The location of the X-specific repeats makes them potentially useful for future investigations of discases mapping to the distal long arm of the X chromosome, such as the fragile X syndrome.     

Physical mapping of nine Xq translocation breakpoints and identification of XPNPEP2 as a premature ovarian failure candidate gene

Women with balanced translocations between the long arm of the X chromosome (Xq) and an autosome frequently suffer premature ovarian failure (POF). Two "critical regions" for POF which extend from Xq13-->q22 and from Xq22-->q26 have been identified using cytogenetics. To gain insight into the mechanism(s) responsible for ovarian failure in women with X;autosome translocations, we have molecularly characterized the translocation breakpoints of nine X chromosomes. We mapped the breakpoints using somatic cell hybrids retaining the derivative autosome and densely spaced markers from the X-chromosome physical map. One of the POF-associated breakpoints in a critical region (Xq25) mapped to a sequenced PAC clone. The translocation disrupts XPNPEP2, which encodes an Xaa-Pro aminopeptidase that hydrolyzes N-terminal Xaa-Pro bonds. XPNPEP2 mRNA was detected in fibroblasts that carry the translocation, suggesting that this gene at least partially escapes X inactivation. Although the physiologic substrates for the enzyme are not known, XPNPEP2 is a candidate gene for POF. Our breakpoint mapping data will help to identify additional candidate POF genes and to delineate the Xq POF critical region(s).     

Tissue-specific heterogeneity in DNA replication patterns of human X chromosomes

Regional DNA replication kinetics in human X chromosomes have been analysed using BrdU-33258 Hoechst-Giemsa techniques in five cell types from human females: amniotic fluid cells, fetal and adult skin fibroblasts, and fetal and adult peripheral lymphocytes. In all cell types, the late-replicating X chromosome can be distinguished from its active, earlyreplicating homologue, and both the early and late X exhibit temporally and regionally characteristic internal sequences of DNA replication. The replication pattern of the early X in amniotic fluid cells and skin fibroblasts is similar to that of the early X in lymphocytes, although certain discrete regions are later-replicating in these monolayer tissue culture cells than are the corresponding regions in lymphocytes. However, DNA replication kinetics in late X chromosomes from amniotic fluid cells and skin fibroblasts are strikingly different from those observed in lymphocytes with respect both to the initiation and termination of DNA synthesis. The predominant late X pattern observed in 80–95% of lymphocytes, in which replication terminates in the long arm in bands Xq21 and Xq23, was never seen in amniotic fluid cells or skin fibroblasts. Instead, in these cell types, bands Xq25 and Xq27 are the last to complete DNA synthesis, while bands Xq21 and Xq23 are earlier-replicating; this pattern is similar to the alternative replication sequence observed in 5–20% of lymphocyte late X chromosomes. This replication sequence heterogeneity is consistent with the existence of tissue-specific influences on the control of DNA replication in human X chromosomes.     

Tandem duplication dup(X)(q13q22) in a male proband inherited from the mother showing mosaicism of X-inactivation

Summary An aberrant X chromosome containing extra material in the long arm was observed in a psychomotoric retarded boy and his healthy, short-statured mother. The proband showed generalized muscular hypotony, growth retardation, and somatic anomalies including hypoplastic genitalia and cryptorchism.Chromosomal banding techniques suggested a tandem duplication of the segment Xq13Xq22.In the mother the vast majority of lymphocytes showed late replication of the aberrant X chromosome. Some of her cells, however, contained an apparently active aberrant X. Both the early- and late-replicating aberrant X exhibited late replication patterns very similar to those described for normal X chromosomes in lymphocytes. Asynchrony of DNA replication among the two segments Xq13Xq22 in the dup(X) was never observed.We consider that the clinical picture of the proband is caused by an excess of active X material.     

RFLPs研究三例X染色体结构异常的起源和形成机理

本文对三例X染色体结构异常46,X,dup(X)(p21);46,X,del(X)(p11);46,X,i(Xq)患者及其父母,用X染色体短臂或长臂上的限制性片段长度多态性(RFLPs)作为遗传标记,研究了异常X染色体的起源和形成机理。结果表明,dup(X)(p21)和del(X)(p11)起源于父方,而i(Xq)起源于母方。dup(X)(p21)是由X染色体姊妹染色单体不均等的互换所引起的,del(X)(p11)是由于X染色体断裂后丢失所致,i(Xq)的发生是由于卵母细胞X染色体着丝粒错分裂。