A Y/15 translocation in a 45,X male with Prader-Willi syndrome

We report a male neonate with a 45 X karyotype; the long arm of a chromosome 15 was translocated onto the proximal long arm of the Y chromosome. Breakpoints were identified by in situ fluorescence hybridization (FISH) on the proximal 15q13 and Yq11.2. The derivative chromosome has no primary centromere. Clinical features were compatible with Prader-Willi syndrome. This is the first report case ofmonosomy 15q and Yq deletion with Prader-Willi syndrome.     

Interstitial deletion of chromosome 9q with coexistence of the deleted segment as a ring chromosome. A case report.

In a mentally retarded female an interstitial deletion of a chromosome 9 and an additional ring chromosome was shown, which by positive hybridisation with a no 9 library was considered to be the excised segment. The functional centromere and C and DA/DAPI positive material as well on the ring chromosome are explained by a break within the centromere close to the constitutive heterochromatin and supports the hypothesis of "latent" centromere(s).     

Transmission of a fully functional human neocentromere through three generations

An unusual Y chromosome with a primary constriction inside the long-arm heterochromatin was found in the amniocytes of a 38-year-old woman. The same Y chromosome was found in her husband and brother-in-law, thus proving that it was already present in the father. FISH with alphoid DNA showed hybridization signals at the usual position of the Y centromere but not at the primary constriction. Centromere proteins (CENP)-A, CENP-C, and CENP-E could not be detected at the site of the canonic centromere but were present at the new constriction, whereas CENP-B was not detected on this Y chromosome. Experiments with 82 Y-specific loci distributed throughout the chromosome confirmed that no gross deletion or rearrangement had taken place, and that the Y chromosome belonged to a haplogroup whose members have a mean alphoid array of 770 kb (range 430-1,600 kb), whereas that of this case was approximately 250 kb. Thus, this Y chromosome appeared to be deleted for part of the alphoid DNA. It seems likely that this deletion was responsible for the silencing of the normal centromere and that the activation of the neocentromere prevented the loss of this chromosome. Alternatively, neocentromere activation could have occurred first and stimulated inactivation of the normal centromere by partial deletion. Whatever the mechanism, the presence of this chromosome in three generations demonstrates that it functions sufficiently well in mitosis for male sex determination and fertility and that neocentromeres can be transmitted normally at meiosis.     

A tdic(5;15)(p31;p11) chromosome showing variation for constriction in the centromeric regions in a patient with the cri du chat syndrome.

Some dicentric chromosomes show only one primary constriction at metaphase and behave in cell division as if they are monocentric. The few previous reports of tdic (translocation dicentric) chromosomes showing one morphologic indicate that among the cells of an individual the same centromere consistently shows the primary constriction. The present case deals with a tdic(5;15)(p13;p11) chromosome that is an exception to this pattern. Scoring 98 GTG-, C-, and QFQ-banded metaphases specifically for primary constrictions revealed 15 (15%) containing a tdic chromosome with a single primary constriction. Among these chromosomes, 8 (8%) were at the chromosome 15 centromere and 7 (7%) were at the chromosome 5 centromere. The remaining 83 (85%) tdic chromosomes showed two primary constrictions. We analyzed a total of 172 metaphases from peripheral blood, and all except 3 (1.7%) contained the tdic chromosome. Among these three cells, the tdic chromosome was broken in two and absent in one, which indicates that there was some unstable separation of this dicentric in cell division. In two metaphases, there was a chromatid gap at the site of one centromere. Possibly, the absence of certain primary constrictions was associated with deletion of centromeres. This mechanism may be a continual source for additional centromere inactivation during the life of this patient. This case demonstrates that for some dicentrics either centromere may become nonfunctional and inactivation can occur more than once within an individual. The karyotype of this patient was 45,XX,tdic(5;15)(p31;p11). Thus, she was monosomic for about 3/4 of the chromosome 5 short arm. Clinically, this infant had a shrill catlike cry and facies of the cri du chat syndrome.     

Molecular and cytogenetic characterisation of a small interstitial de novo 20p13-->p12.3 deletion in a patient with severe growth deficit

We report on a small de novo interstitial deletion of the short arm of chromosome 20, 46,XY,del(20)(p12.3p13), in a young boy with hypotonia, moderate development delay, mild facial dysmorphism and severe growth failure. This patient did not show major features of Alagille-Watson Syndrome (AWS) which are common in more proximal 20p deletions. Standard and high resolution chromosome banding analysis revealed an apparent terminal deletion. Nevertheless, using chromosomal fluorescent in situ hybridization (FISH) and molecular analysis with polymorphic markers, we demonstrated that the abnormal chromosome resulted from a de novo interstitial deletion of paternal origin spanning from D20S842 to D20S900 and covering approximately 6 Mb. These findings indicate that a karyotype can lead to insufficient characterization of an apparently terminal deletion, and that one or a few genes in 20p13-->p12.3 bands are important for normal growth.     

Human telomeric 6; 19 translocation chromosome with a tendency to break at the fusion point

The behavior of a translocation chromosome t(6; 19) in the lymphocytes of a mentally retarded woman with other anomalies has been analyzed. The two chromosomes were attached at the telomeres of their short arms without any apparent deletion. The centromere of chromosome 19 was marked by a primary constriction and the site of the centromere of chromosome 6 by a C-band, but no constriction. The translocation chromosome showed two primary constrictions once in 8,800 metaphases, probably resulting from mitotic crossing-over. One or both chromatids of the translocation chromosome were broken at the attachment point with a frequency of 1/733 cells. In addition, the chromosome was often bent at this point and the translocated chromosomes 19 and 6 showed a differential spiralization. In this characteristic as well as the weakness of the fusion point, this chromosome differed from other translocations; the fusion obviously was not as firm as in translocations in general. The broken-off chromosome 6 did not regain a primary constriction, but had the appearance of a large acentric fragment. The segregation of the translocation chromosome and the fragment gave rise to a complicated mosaicism with various levels of ploidy for the fragment lacking a functional centromere. The data are in quantitative agreement with the equilibrium expectations under the assumption that each fragment goes to either pole at random in mitosis and that cells divide at the same rate regardless of ploidy. The high rate of nondisjunction of the fragment showed that the inactivated centromere of the translocation chromosome did not regain its activity when chromosome 19 with the functional centromere became separated from it. — The fragility and the behavior of the translocation chromosome and the production of telomeric associations are briefly discussed.     

Loss of heterozygosity in hypotriploid cell cultures from testicular tumours

Summary We have established cell lines with a hypotriploid chromosome number from four testicular tumours. Each line had at least one Y chromosome and most of the informative centromere and enzyme markers were heterozygous implying that the tumours originated from germ cells before the first meiotic division. The small metacentric marker chromosome (i12p), specific for testicular tumours, was present in all tumour cell lines and up to three copies were found in some lines. Rearrangements of chromosome 1 and 11 were each found in three out of four tumours. The rearrangements of chromosome 1 all resulted in duplication of 1q and deletion of short-arm material from the same chromosome giving loss of heterozygosity for enzyme markers on 1p. Loss of satellite material from chromosome 13 and the centromere region of chromosome 9 were found in single cases. This study shows that even where the chromosome number of tumour cells is near triploid, regions of the genome can be deleted. The chromosomes most frequently involved in rearrangements, 1, 11, and 12 all contain sites of ras oncogenes and it is suggested that loss of normal alleles could result in homozygosity for mutant oncogenes which may play a part in tumour progression.     

High-resolution cytological mapping of the long arm of chromosome 5A in common wheat using a series of deletion lines induced by gametocidal (Gc) genes of Aegilops speltoides

Gametocidal (Gc) genes of Aegilops in the background of the wheat genome lead to breakage of wheat chromosomes. The Q gene of wheat was used as a marker to select 19 deletion lines for the long arm of chromosome 5A of common wheat, Triticum aestivum cv. Chinese Spring (CS). The extents of deleted segments were cytologically estimated by the C-banding technique. The DNAs of deletion lines were hybridized with 22 DNA probes recognizing sites on the long arm of the chromosome (5AL) to determine their physical order. Based on the breeding behavior of the deletion lines, the location of a novel gene (Pv, pollen viability) affecting the viability of the male gamete was deduced. The segment translocated from 4AL to 5AL in CS was cytologically estimated to represent 13% of the total length of 5AL. Although DNA markers were almost randomly distributed along the chromosome arm, DNA markers located around the centromere and C-banded regions were obtained only rarely. Some deletion lines were highly rearranged in chromosome structure due to the effect(s) of the Gc gene. Applications of Gc genes for manipulating wheat chromosomes are discussed.     

High-resolution cytological mapping of the long arm of chromosome 5A in common wheat using a series of deletion lines induced by gametocidal (Gc) genes of Aegilops speltoides

Gametocidal (Gc) genes of Aegilops in the background of the wheat genome lead to breakage of wheat chromosomes. The Q gene of wheat was used as a marker to select 19 deletion lines for the long arm of chromosome 5A of common wheat, Triticum aestivum cv. Chinese Spring (CS). The extents of deleted segments were cytologically estimated by the C-banding technique. The DNAs of deletion lines were hybridized with 22 DNA probes recognizing sites on the long arm of the chromosome (5AL) to determine their physical order. Based on the breeding behavior of the deletion lines, the location of a novel gene (Pv, pollen viability) affecting the viability of the male gamete was deduced. The segment translocated from 4AL to 5AL in CS was cytologically estimated to represent 13% of the total length of 5AL. Although DNA markers were almost randomly distributed along the chromosome arm, DNA markers located around the centromere and C-banded regions were obtained only rarely. Some deletion lines were highly rearranged in chromosome structure due to the effect(s) of the Gc gene. Applications of Gc genes for manipulating wheat chromosomes are discussed.     

Mosaicism for an ectopic NOR at 8pter and a complex rearrangement of chromosome 8 in a patient with severe psychomotor retardation

We describe a 3-year-old girl with severe delays in mental and motor skills, a history of generalized seizures, and subtle dysmorphic features. Conventional cytogenetics revealed a mosaic karyotype. A de novo ectopic NOR at the telomeric region of the short arm of one chromosome 8 (8ps) was found in 90% of lymphocyte and in 98% of fibroblast metaphases. A small NOR-bearing marker chromosome and a large derivative chromosome 8 without short arm satellites (der(8)) were present in the remaining cells. FISH with a probe specific for centromeres 14 and 22 labeled both the telomeric region of 8ps and the small marker centromere. Der(8) included an inverted duplication of 8p and a rearranged duplication of 8q but lacked a second centromere. A subtelomeric probe for 8p revealed a cryptic deletion in 8ps and der(8). Thus, the karyotype represents a combination of submicroscopic partial monosomy 8pter and mosaic trisomy 8.     

X-X translocation in a patient with gonadal dysgenesis and the problem of phenotype-karyotype correlations

Summary A sex-chromatin-positive woman without stunted growth, but with primary amenorrhea, and some stigmas of pure gonadal dysgenesis had the chromosome constitution 45,X/46,Xt(X;X)(q27;q27). The abnormal chromosome formed a large Barr body and was late-labeling. The chromosome consisted of two X chromosomes attached by their long arms (end-to-end), both apparently having the partial distal deletion. Both centromeric regions showed C-staining but only one constriction. The chromosome is interpreted as an isodicentric with only one centromere functioning. Some problems of phenotype-karyotype correlations are discussed.     

In search of a 9q13 latent centromere in 9qh polymorphic inversions

In search of a 9q13 latent centromere in 9qh polymorphic inversions: The presence of alphoid sequences in 9q13 has prompted the suggestion that such a region could harbor a latent centromere which under certain circumstances may appear as a neocentromere. We tested this hypothesis by means of FISH with a centromere 9-specific alphoid probe in lymphocyte metaphases from 13 unrelated individuals with a 9qh polymorphic inversion. Since all inverted chromosomes had the alphoid signal onto the primary constriction, it was not possible to identify any neocentromere . We believe, however, that the number of cases was not enough to conclude that all the polymorphic inversions of chromosome 9 are genuine.     

Reliability and efficiency of interphase-fish with alpha-satellite probe for detection of aneuploidy

Early diagnosis is very important in pre- and postnatal diagnosis of Down syndrome. This study examines the use of fluorescence in situ hybridization (FISH) to detect trisomy 21 in interphase nuclei and metaphase chromosome obtained from fifty-four Down syndrome patients with a regular type trisomy 21. Three of them showed six hybridization signals on both interphase nuclei and metaphase spreads instead of five signals corresponding to two chromosomes 13 and three chromosomes 21 although they were cytogenetically trisomy 21. Simultaneous application of probe combination revealed that one of the extra signals of chromosomes 13/21 a-satellite probe was located on chromosome 22 in two cases and one extra signal on chromosomes 15 in one case. In addition, another case showed four hybridization signals on both interphase nuclei and metaphase spreads instead of five signals, indicating deletion of the chromosome specific alpha-satellite DNA sequence of chromosome 13/21. These centromeric sequence changes may have pathological significance in the appearance of aneuploidy because they may be involved in the important centromere function.     

Chromosome Y Centromere Array Deletion Leads to Impaired Centromere Function

The centromere is an essential chromosomal structure that is required for the faithful distribution of replicated chromosomes to daughter cells. Defects in the centromere can compromise the stability of chromosomes resulting in segregation errors. We have characterised the centromeric structure of the spontaneous mutant mouse strain, BALB/cWt, which exhibits a high rate of Y chromosome instability. The Y centromere DNA array shows a de novo interstitial deletion and a reduction in the level of the foundation centromere protein, CENP-A, when compared to the non-deleted centromere array in the progenitor strain. These results suggest there is a lower threshold limit of centromere size that ensures full kinetochore function during cell division.     

Precocious Meiotic Centromere Separation of a Novel Yeast Chromosome

In Saccharomyces cerevisiae, a reciprocal translocation between chromosome II and a linear plasmid carrying a centromere (CEN6) has split chromosome II into two fragments: one, approximately 530 kilobase pairs (kbp) in size, has the left arm and part of the right arm of chromosome II; the other, a telocentric fragment approximately 350 kbp in size, has CEN6 and the rest of the right arm of chromosome II. A cross of this yeast strain with a strain containing a complete chromosome II exhibits a high frequency of precocious centromere separation (separation of sister chromatids during meiosis I) of the telocentric fragment. Precocious centromere separation is not due to the position of the centromere per se, since diploids that are homozygous for both fragments of chromosome II segregate the telocentric fragment with normal meiotic behavior. The precocious centromere separation described here differs from previously described examples in that pairing and synapsis of this telocentric chromosome seem to be normal. One model of how centromeres function in meiosis is that replication of the centromere is delayed until the second meiotic division. Data presented in this paper indicate that replication of the centromere is complete before the first meiotic division. The precocious separation of the centromere described here may be due to improper synapsis of sequences flanking the centromere.     

Rad51 suppresses gross chromosomal rearrangement at centromere in Schizosaccharomyces pombe

Centromere that plays a pivotal role in chromosome segregation is composed of repetitive elements in many eukaryotes. Although chromosomal regions containing repeats are the hotspots of rearrangements, little is known about the stability of centromere repeats. Here, by using a minichromosome that has a complete set of centromere sequences, we have developed a fission yeast system to detect gross chromosomal rearrangements (GCRs) that occur spontaneously. Southern and comprehensive genome hybridization analyses of rearranged chromosomes show two types of GCRs: translocation between homologous chromosomes and formation of isochromosomes in which a chromosome arm is replaced by a copy of the other. Remarkably, all the examined isochromosomes contain the breakpoint in centromere repeats, showing that isochromosomes are produced by centromere rearrangement. Mutations in the Rad3 checkpoint kinase increase both types of GCRs. In contrast, the deletion of Rad51 recombinase preferentially elevates isochromosome formation. Chromatin immunoprecipitation analysis shows that Rad51 localizes at centromere around S phase. These data suggest that Rad51 suppresses rearrangements of centromere repeats that result in isochromosome formation.     

Congenital heart defect and mental retardation in a patient with a 13q33.1-34 deletion

13q deletion syndrome is a rare genetic disorder caused by deletions of the long arm of chromosome 13. Patients with 13q deletion display a variety of phenotypic features. We describe a one-year-old female patient with congenital heart defects (CHD), facial anomalies, development and mental retardation. We identified a 12.75Mb deletion in chromosome region 13q33.1-34 with high resolution SNP Array (Human660W-Quad, Illumina, USA). This chromosome region contains about 55 genes, including EFNB2, ERCC5, VGCNL1, F7, and F10. Comparing our findings with previously reported 13q deletion patients with congenital heart defects, we propose that the 13q33.1-34 deletion region might contain key gene(s) associated with cardiac development. Our study also identified a subclinical deficiency of Factors VII and X in our patient with Group 3 of 13q deletion syndrome.     

Nucleolus organizer region--centromere translocation

A karyotype 45,XX,-13,-15,+psudic (13;15)(p12.9;11.200) was observed in a young woman after two spontaneous miscarriages. After R-, C-, and NOR - banding - the rearranged element was shown to include: the long arm, the active centromere, and the NOR of chromosome 13, followed by the inactivated centromere, and the long arm of chromosome 15.     

Partial deletion of alpha satellite DNA associated with reduced amounts of the centromere protein CENP-B in a mitotically stable human chromosome rearrangement.

A familial, constitutionally rearranged human chromosome 17 is deleted for much of the DNA in its centromeric region but retains full mitotic centromere activity. Fluorescence in situ hybridization, pulsed-field gel electrophoresis, and Southern blot analysis of the residual centromeric region revealed a approximately 700-kb centromeric array of tandemly repeated alpha satellite DNA that was only approximately 20 to 30% as large as a normal array. This deletion was associated with a reduction in the amount of the centromere-specific antigen CENP-B detected by indirect immunofluorescence. The coincidence of the primary constriction, the small residual array of alpha satellite DNA, and the reduced amount of detectable CENP-B support the hypothesis that CENP-B is associated with alpha satellite DNA. Furthermore, the finding that both the deleted chromosome 17 and its derivative supernumerary fragment retained mitotic function and possess centromeric protein antigens suggests that human centromeres are structurally and functionally repetitive.     

Interstitial deletion and ring chromosome derived from 19q. Proximal 19q trisomy phenotype.

A small supernumerary ring chromosome has been found in a boy with overweight, dysmorphic facies and mental retardation. His mother had an interstitial deletion of the long arm of chromosome 19 and the same ring chromosome. By means of fluorescence in situ hybridization the ring chromosome was shown to be derived from the deleted chromosome, after the occurrence of two breaks: one in the centromere region, the other in the q-arm of chromosome 19.