Jumping translocation in a phenotypically normal female

Isochromosome Yp and jumping translocation of Yq resulting in five cell lines in an infertile male: a case report and review of the literature

Background

Jumping translocations are a rare type of mosaicism in which the same portion of one donor chromosome is translocated to several recipient chromosomes. Constitutional forms of jumping translocations are rare, and the 48 cases reported to date have been associated with both normal and abnormal phenotypes. Concurrence of isochromosome (i) of one arm and translocation of the other is also rare, with seven reported cases. We describe a unique case involving concurrence of i(Yp) and a jumping translocation of Yq to the telomere of chromosomes 12q and 17q, which resulted in five cell lines.

Case presentation

The patient, an otherwise healthy 35-year-old man, was referred for cytogenetic studies because of absolute azoospermia. He had elevated levels of follicle stimulating hormone and luteinizing hormone, consistent with abnormal spermatogenesis, and decreased levels of free testosterone and inhibin B. G-banded chromosome analysis revealed a mosaic male karyotype involving five abnormal cell lines. One of the cell lines showed loss of chromosome Y and presence of i(Yp) as the sole abnormality. Three cell lines exhibited jumping translocation: two involved 17qter, and the other involved 12qter as the recipient and Yq as the common donor chromosome. One of the cell lines with der(17) additionally showed i(Yp). The other der(17) and der(12) cell lines had a missing Y chromosome. All five cell lines were confirmed by FISH. Subtelomric FISH study demonstrated no loss of chromosome material from the recipient chromosomes at the translocation junctions.

Conclusions

We postulate that a postzygotic pericentromeric break of the Y chromosome led to formation of isochromosome Yp, whereas Yq formed a jumping translocation through recombination between its internal telomere repeats and telomeric repeats of recipient chromosomes. This in turn led to either pairing or an exchange at the complimentary sequences. Such translocation junctions appear to be unstable and to result in a jumping translocation. Cryptic deletion or disruption of AZF (azoospermic factor) genes at Yq11 during translocation or defective pairing of X and Y chromosomes during meiosis, with abnormal sex vesicle formation and consequent spermatogenetic arrest, might be the main cause of the azoospermia in our patient.

The conundrum of a jumping translocation (JT) in CVS from twins and review of JTs

Jumping translocations (JTs) are rare constitutional or acquired rearrangements involving a donor and several receiver chromosomes. They may be inherited or de novo. JTs can be found as a cultural artifact, in normal individuals or in pathological conditions. The clinical consequences range from spontaneous abortion, loss of fetus, chromosome syndrome, congenital abnormalities, and infertility to malignancy. Considering the breakpoints of JTs, they are localized predominantly in repeat regions such as pericentromeric, centromeric, subtelomeric, telomeric, and occasionally interstitial regions that may be in a low copy repeats (LCR) or in a telomere like sequence. Differences between the constitutional and acquired JTs donor breakpoints suggest an independent mechanism in their formation. In this review, a new JT involving a donor chromosome 18p10qter and recipients 17q25qter or 1q25qter found by CVS of a twin pregnancy is described. This case illustrates the diagnostic challenges posed by JTs.In this study, our knowledge on JTs is consolidated to improve identification, management, and counseling.

Jumping translocation in a phenotypically normal male: A study of mosaicism in spermatozoa, lymphocytes, and fibroblasts

Both Robertsonian translocations, rob(13;13) and rob(13;15), (in the present case defined as dic(13;15)), are rare chromosomal rearrangements and there is scarce information regarding their behavior during meiosis. In this report we describe a man with mosaicism for two cell lines, each cell line containing a different de novo Robertsonian translocation with the common breakpoint in the centromeric region on chromosome 13. The karyotype was finally defined as: 45,XY,rob(13;13)(q10;q10)[29]/45,XY,dic(13;15)(p11.2;p12)[22], a phenomenon referred to as jumping translocation. The relative occurrence of the two clones in lymphocytes and fibroblasts as well as the meiotic segregation in spermatozoa and the mechanism of formation were studied using karyotype analysis, fluorescence in situ hybridization (FISH), and quantitative fluorescence-PCR. Karyotype analysis of cultured lymphocytes revealed 57% rob(13;13) cells and 43% dic(13;15) cells and for cultured skin fibroblasts the figures were almost identical (56% and 44%, respectively). FISH analysis showed 55% balanced nuclei for unselected spermatozoa and after swim-up selection the number of balanced spermatozoa decreased to 41%. In addition, 16% of the unselected spermatozoa and 27% of the spermatozoa after swim-up selection carried an additional chromosome 13, indicating a high risk for a trisomy 13 offspring. Swim-up selection did not increase the number of balanced spermatozoa.

Jumping translocations

Jumping translocations (JT) are uncommon constitutional or acquired chromosome rearrangements involving one donor and several recipient chromosomes. They occur in various pathologic conditions and the mechanism of their formation remains elusive. A review of the literature showed that the major localizations of the breakpoints of JTs in human samples are nonrandomly located in pericentromeric and telomeric regions of chromosomes. Interestingly, comparison of the localization of the chromosomal breakpoints and of presence of interstitial DNA repeats showed differences between constitutional and acquired JTs suggesting differences in the mechanisms for the genesis of JTs and their consequences.

Ring chromosome 18q and jumping translocation 18p in an adult male with hypergonadotrophic hypogonadism

Constitutional jumping translocations (JT) are rare, especially in phenotypically normal individuals. We report on an adult male with partial hypogonadism as the sole phenotypic abnormality with an unusual chromosome abnormality. In this patient, centric fission of chromosome 18 lead to formation of a ring 18q chromosome, while 18p formed a JT through centromere-telomere fusion with chromosome 8q (66%) or 20q (13%). In 21% of cells, the 18p fragment was missing. Fluorescent in situ hybridization revealed the presence of interstitial telomeres at the junction site of the fusion and unequal distribution of the alphoid sequences through the centric fission, leaving a small, yet functional centromere within the ring. We discuss the phenotype of the patient in light of this unusual karyotype.

Mutations in ARHGEF6, encoding a guanine nucleotide exchange factor for Rho GTPases, in patients with X-linked mental retardation

X-linked forms of mental retardation (XLMR) include a variety of different disorders and may account for up to 25% of all inherited cases of mental retardation. So far, seven X-chromosomal genes mutated in nonspecific mental retardation (MRX) have been identified: FMR2, GDI1, RPS6KA3, IL1RAPL, TM4SF2, OPHN1 and PAK3 (refs 2-9). The products of the latter two have been implicated in regulation of neural plasticity by controlling the activity of small GTPases of the Rho family. Here we report the identification of a new MRX gene, ARHGEF6 (also known as alphaPIX or Cool-2), encoding a protein with homology to guanine nucleotide exchange factors for Rho GTPases (Rho GEF). Molecular analysis of a reciprocal X/21 translocation in a male with mental retardation showed that this gene in Xq26 was disrupted by the rearrangement. Mutation screening of 119 patients with nonspecific mental retardation revealed a mutation in the first intron of ARHGEF6 (IVS1-11T-->C) in all affected males in a large Dutch family. The mutation resulted in preferential skipping of exon 2, predicting a protein lacking 28 amino acids. ARHGEF6 is the eighth MRX gene identified so far and the third such gene to encode a protein that interacts with Rho GTPases.

Jumping translocations involving 11q in a non-Hodgkin lymphoma

This paper presents the results of a cytogenetic analysis in an 11-year-old boy with non-Hodgkin lymphoma. The investigation was performed on slides obtained from short-term culture of lymph node cells. The analyses revealed an abnormal clone with loss of Y, gain of an X chromosome, t(3;22), trisomy 11, and three cytogenetically-related subclones with jumping translocations involving 11q13 as the common breakpoint region. This region is an unusual site of chromosome breakage in jumping translocations, and has not been reported thus far. Contrary to most published reports, the jumping translocation in our patient is associated with long survival.

Two children with acute lymphoblastic leukemia and "jumping" translocations: both involve 1q23 as the donor breakpoint

"Jumping" translocations (JT) are relatively rare and are associated with poor prognosis. We report two male patients with childhood acute lymphoblastic leukemia (ALL) and abnormal cell lines detected on bone marrow cytogenetics. Diagnostic marrow cytogenetics were not available for either patient. In patient 1, approximately 11 years after diagnosis, cytogenetics revealed a single translocation, t(1;2)(q23;q32), which was followed by translocations t(1;22)(q23;p11) and t(1;1)(q23;q21.3). In patient 2, two translocations were present together, t(1;6)(q23;p21.3) and t(1;11)(q23;q21), 12 years after diagnosis. The unbalanced JTs in both patients resulted in partial trisomy for (1)(q23-->qter). Both died within 1-2 years after the appearance of the JT. Our patients provide additional support for chromosome 1q preferential involvement in JTs, and that their appearance is associated with a poor prognosis.

Centromere-telomere (12;8p) fusion, telomeric 12q translocation, and i(12p) trisomy

The concurrence of a short arm isochromosome and a translocation of the entire long arm of the same chromosome to a telomere of another chromosome, implying trisomy for 4p, 5p, 7p, 9p, 10p or 12p, has been described in 13 patients. We have now used fluorescence in situ hybrization (FISH) to better characterize one of these rearrangements in which 12q was translocated to 8pter, whereas 12p was converted into an isochromosome. An alphoid centromere-12 repeat gave a strong signal on the i( 2p) and a weak but distinct signal at the breakpoint junction of the der(8), whereas the pantelomeric probe revealed three clear hybridization sites on the der(8): one at each end and another at the breakpoint junction. These findings suggest that the prime event was a post-fertilization centric fission of chromosome 12 leading to the 12q translocation via a real centromere telomere fusion and the i(12p). Alternatively, the crucial event may have been a centromere telomere recombination. An interstitial telomere has been documented by means of FISH at the breakpoint junction of the sole derivative usually present in 20 constitutional translocations including eight with a jumping behavior. In addition, six other telomeric translocations defined by banding methods, including another case of 12q translocation/i(12p), have also been jumping ones. These telomeric translocations have been de noro events and their proneness to exhibit a jumping behavior appears to be independent of the involved chromosomes, size of the translocated segments, and concomitant abnormalities.

Jumping translocations of 3q in acute promyelocytic leukemia

Jumping translocation is a rare phenomenon, seldom reported to occur in cancer. A complex four-way translocation involving chromosomes 3, 9, 15, and 17 was identified in the chromosome study on a patient with a history of an acute promyelocytic leukemia (APL). In the follow-up studies, the same complex rearrangement exhibited a jumping translocation between chromosomes 3 and 9 in one clone and 3 and 6 in another clone. This is the first reported case of jumping translocation in APL.

Jumping translocation with partial duplications and triplications of chromosomes 7 and 15

We report a 2-year-old female with seizures, mild dysmorphic features and a jumping translocation involving chromosome 15 that results in multiple cell lines with partial duplications and triplications of chromosomes 7 and 15. Fluorescent in situ hybridization (FISH) and chromosome microdissection were used to identify the complex nature of the jumping translocation. Interstitial telomeres were observed at the jumping translocation sites. The jumping chromosome rearrangement was also found to have a partial duplication of 7p as demonstrated by chromosome microdissection. Despite these partial duplications and triplications of chromosomes 7 and 15, the child does not have major birth defects. She does have mild sensorimotor delays. A review of non-Robertsonian jumping translocations is provided.