A male pseudohermaphrodite with a dicentric Y chromosome

Summary A 13-year-old male pseudohermaphrodite (mixed gonadal dysgenesis, unilateral testicular differentiation) was found to be a chromosomal mosaic of the 45, XO/46, XY type, the Y chromosome being a symmetrical dicentric chromosome. Presumed Y chromosomes similar to this one have been observed before, but their identification was not supported by autoradiographic data. In the present study the identification of the dicentric as a Y chromosome was supported by observing a relatively late DNA replication during the S period. The differentiation of testicular tissue on one side may be related to the presence of short arm material of the Y chromosome in the genome of the XY dic cells.This study was supported by a Research Grant from the National Institute of Child Health and Human Development (1RO1-HD0999-03) and by a Public Health Service Training Grant in Pediatric Endocrinology and Metabolic Diseases (2T1-AM-5190).     

A dicentric chromosome of Drosophila melanogaster showing alternate centromere inactivation

Dicentric chromosomes are rarely found, because they interfere with normal cell division causing chromosome instability. By in situ hybridization of region-specific heterochromatic yeast artificial chromosomes we have found that the artificially generated C(1)A chromosome of Drosophila melanogaster has two potential centromeres: one carries all the sequences of the centromere of the Y chromosome and the other carries only a part of the Y centromeric region that is rich in telomere-related sequences. Immunostaining with anti-Bub1 (a kinetochore-specific marker) shows that, in spite of the differences in sequence, both centromeres can be active although as a rule only one at a time. In a small fraction of the chromosomes centromere inactivation is incomplete, giving rise to true dicentric chromosomes. The centromere inactivation is clonally inherited, providing a new example of epigenetic chromosome imprinting and the possibility of genetically dissecting this process. The involvement of telomere-related sequences in centromere function is discussed. Received: 15 September 1999; in revised form: 21 November 1999 / Accepted: 24 December 1999     

Short arm dicentric Y chromosome with associated statural defects in a sterile man

Summary A short arm dicentric Y chromosome is described as the predominant cell line in a sterile man. The patient also presents with short stature. Tooth development appears normal. Only Sertoli cells are present in the seminiferous tubules. It is suggested that the function of the gene controlling spermatogenesis in Yq11 in man might be to prevent proliferation or migration of germ cells to the gonad of the early embryo.     

A dicentric iso (Y) chromosome in an infertile male

A dicentric Y chromosome was detected in a 30-year-old azoospermic male patient who was found to be mosaic for 45,X/46,X,dic Y(qter----p11::p11----qter). The dicentric iso (Y) chromosome was identified conclusively with C-banding, G-banding and Q-banding techniques. The relationship of structural abnormalities of the Y chromosome and azoospermia is discussed.     

Centromere inactivation in a case of turner variant with two dicentric iso-long arm Y chromosomes

Summary A 6-year-old girl of small stature and with some features of Turner's syndrome was found to have a karyotype with two-thirds of the cells possessing one, and one-third with two dicentric iso-long arm Y chromosomes. In metaphases with 46 chromosomes the majority of the abnormal Ys exhibited two primary constrictions. In cells with 47 chromosomes both isochromosomes prevalently had only one active centromere.     

An unusual dicentric Y chromosome with a functional centromere with no detectable alpha-satellite

We describe an unusual marker chromosome Y. This marker is present in 5% of the lymphocytes of a dysgenetic woman showing a mosaic karyotype 45,X/46,XY/ 47,XY+mar. Q-banding revealed that the marker was morphologically identical to the Y chromosome of the patient but presented the primary constriction in the heterochromatic region. C-banding confirmed that the heterochromatic region was C-positive; furthermore, it showed two spots in the euchromatic region in a position corresponding to that of the centromere in the normal Y Fluorescence in situ hybridization with the centromere-specific probe pDP 97 and the pancentromeric alpha-satellite probe 2730 failed to detect any signal at the primary constriction site. To improve the characterization of the marker chromosome, hybridization was performed using pDP 105, a probe located on the short arm of the Y chromosome, together with chromosome-Y- specific paint-hybridizing to the single sequence spanning the Y short arm. In both cases, positive signals telomeric to the inactive centromere were observed. Possible mechanisms resulting in the formation of the marker chromosome are discussed.     

Fluorescence pattern of a dicentric Y

Summary The different appearence of a dicentric Y, as shown with the fluorescence technique, is described, as well as the findings in cells of buccal mucosa, hairroots and peripheral blood.

---

Zusammenfassung Das Fluoreszenzmuster und die unterschiedliche Morphologie eines dizentrischen Y werden beschrieben. Fluoreszierende Körperchen wurden in Mundschleimhautabstrichen, Haarwurzelzellen und Blutausstrichen aus peripherem Blut beobachtet.

     

Molecular investigation of a dicentric 13;17 chromosome found in a 21-week gestation fetus with multiple congenital abnormalities

We report a 21-week gestation fetus terminated because of multiple congenital abnormalities seen on ultrasound scan, including ventriculomegaly, possible clefting of the hard palate, cervical hemivertebrae, micrognathia, abnormal heart, horseshoe kidney and a 2-vessel umbilical cord. On cytogenetic examination, the fetus was found to have a male karyotype with 45 chromosomes with a dicentric chromosome, which appeared to consist of the long arms of chromosomes 13 and 17. Molecular genetic investigations and fluorescence in situ hybridization (FISH) unexpectedly showed that the derivative chromosome contained two interstitial blocks of chromosome 17 short arm sequences, totalling approximately 7 Mb, between the two centromeres. This effectively made the fetus monosomic for approximately 15 Mb of 17p without the concurrent trisomy for another chromosome normally seen following malsegregation of reciprocal translocations. It also illustrates the complexity involved in the formation of some structurally abnormal chromosomes, which can only be resolved by detailed molecular investigations.     

Segregation of acrocentric chromosome association in familial dicentric Robertsonian translocation t(14p;22p), aneuploidy (trisomy-21) and heteromorphism

The frequency and types of acrocentric chromosome association were quantitatively analysed in a Down syndrome child with unusual karyotype, 46, XX, -14, -22, t dic (14p;22p), +21, 21S+. Father and 4 sibs were heterozygous carriers for t dic (14p;22p). The variant 21S+ was inherited from the mother. The occurrence of translocation and trisomy in the same individual is extremely rare. Acrocentric chromosome association was analysed in this interesting family to understand the interrelationship of acrocentric chromosome association, Robertsonian translocation and heteromorphism, as possible predisposing factors for nondisjunction. Our findings suggest that acrocentric chromosome association is a heritable and nonrandom phenomenon. Heterozygous carriers for translocations and variants are likely to be at increased risk of nondisjunction. Long term family studies will enable to ascertain the causal-relationship of these factors more precisely.     

Quinacrine mustard fluorescence of a second Y chromosome in a Y-autosomal translocation

Summary Screening buccal smears from 97 prisoners by the quinacrine mustard technique revealed one XYY-individual and one Y-autosomal translocation of a second Y chromosome with a 46,XY, D-,t (?15q;Yq)+ karyotype. The translocation chromosome could be identified by its intense fluorescence of the short arm in all 75 metaphases examined.

---

Zusammenfassung Untersuchungen von Abstrichen der Mundschleimhaut von 97 Gefängnisinsassen mit der Quinacrine-Mustard-Methode führten zur Aufdeckung eines XYY-Karyotyps und einer Y-autosomalen Translokation eines zweiten Y-Chromosoms mit einem Karyotyp von 46,XY,D-,t(?15q;Yq)+. Das Translokationschromosom konnte durch helle Fluorescenz des kurzen Armes in allen 75 Metaphasen identifiziert werden.

---

---

This work was supported in part by grant number Pa 118/8 from the Deutsche Forschungsgemeinschaft and is part of a thesis by S. F.     

X chromosome inactivation in X autosome translocation carrier cows.

The pattern of X chromosome inactivation in X autosome translocation carries in a herd of Limousin-Jersey crossbred cattle was studied using the reverse banding technique consisting of 5-bromodeoxyuridine incorporation and acridine orange staining and autoradiography on cultures of solid tissues and blood samples exposed to tritiated thymidine. The late-replicating X chromosome was noted to be the normal X in strikingly high proportions of cells in cultures of different tissues from all translocation carriers. It is suggested that the predominance of cells in which the normal X is inactivated may be the result of a post-inactivation selection process. Such a selection process during the prenatal life favouring cells in which the genes of the normal X chromosome remain unexpressed in translocation carrier females may be the mechanism that helps these conceptuses escape the adverse effects of functional aneuploidy. Based on the observation that the translocation carriers of this line of cattle are exclusively females and that there is a higher than expected rate of pregnancy loss, it is also postulated that the altered X chromosome may be lethal to all male conceptuses and to some of their female counterparts.     

Interstitial deletions of repetitive DNA blocks in dicentric human Y chromosomes

Cytogenetic analysis of aberrant human Y chromosomes was done by fluorescence in situ hydbridization (FISH) with Y specific repetitive DNA probes. It revealed an interstitial deletion of different DNA blocks in two dicentric chromosome structures. One deletion includes the total alphoid DNA structure of one centromeric region. The second deletion includes the total repetitive DYZ5 DNA structure in the pericentromeric region of one short Y arm. Both dicentric Y chromosomes were iso(Yp) chromosomes with break and fusion point located in Yq11, the euchromatic part of the long Y arm. Their phenotypic appearance was abnormal, resembling small monocentric Yq-chromosomes in metaphase plates. Mosaic cell lines, usually included in karyotypes with dicentric Y chromosomes, were not observed. It is assumed that both deletion events suppress the kinetochore activity in one Y centromeric region and thus stabilize its dicentric structure. Local interstitial deletion events had not been described in dicentric human Y chromosomes, but are common in dicentric yeast chromosomes. This raises the question of whether deletion events in dicentric human chromosomes are rare or restricted to the Y chromosome or also represent a general possibility for stabilization of a dicentric chromosome structure in human.     

A unique dicentric X;Y translocation with Xq and Yp breakpoints: cytogenetic and molecular studies.

A 32-year-old woman presented with secondary amenorrhea and infertility. She was of normal height and her breasts were well developed, but she had streak gonads; there were no signs of virilization, and she showed no somatic stigmata of Turner syndrome. Chromosome analysis revealed a dicentric X;Y translocation with Xq and Yp breakpoints. Centromeric banding demonstrated a Y centromere and a "suppressed" X centromere. The karyotype of the patient was interpreted as 46,X,t(X;Y)(q22;p11). The Yp breakpoint was confirmed by DNA-hybridization studies with six probes detecting Y-specific sequences. These DNA-hybridization studies were consistent with the presence of the long arm, centromere, and much of the proximal short arm of the Y. The Y-DNA studies of this female also revealed the absence of the distal short arm of the Y chromosome, to which the testis-determining factor has previously been localized.