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Mosaicism for combined tetrasomy of chromosomes 8 and 18 in a dysmorphic child: A result of failed tetraploidy correction?

BMC Medical Genetics200910:42

https://doi.org/10.1186/1471-2350-10-42

Received: 03 October 2008

Accepted: 18 May 2009

Published: 18 May 2009

Abstract

Background

Mosaic whole-chromosome tetrasomy has not previously been described as a cause of fetal malformations.

Case presentation

In a markedly dysmorphic child with heart malformations and developmental delay, CGH analysis of newborn blood DNA suggested a 50% dose increase of chromosomes 8 and 18, despite a normal standard karyotype investigation. Subsequent FISH analysis revealed leukocytes with four chromosomes 8 and four chromosomes 18. The child's phenotype had resemblance to both mosaic trisomy 8 and mosaic trisomy 18. The double tetrasomy was caused by mitotic malsegregation of all four chromatids of both chromosome pairs. A possible origin of such an error is incomplete correction of a tetraploid state resulting from failed cytokinesis or mitotic slippage during early embryonic development.

Conclusion

This unique case suggests that embryonic cells may have a mechanism for tetraploidy correction that involves mitotic pairing of homologous chromosomes.

Background

Unlike meiotic non-disjunctions, mitotic non-disjunctions are rarely observed in humans with the exception of mosaicism for trisomy 8, 9 or 20 [1, 2]. In some cases mosaic trisomy of more than one chromosome have been seen [3]. Such mosaic variegated aneuploidy is due to mitotic errors, often associated with premature centromere division [4]. In contrast to mosaic trisomies, the finding of mosaic whole-chromosome tetrasomy is without precedence. Here we present such a patient; a dysmorphic newborn child with mosaicism of leukocytes containing 50 chromosomes due to tetrasomy of chromosomes 8 and 18. This unique clinical case may have relevance concerning the origin of aneuploidy in cancer [58] because it indirectly suggests that there might be a mechanism for tetraploidy correction during fetal development that involves mitotic pairing of homologous chromosomes.

Case presentation

A baby girl was delivered by cesarean section in week 36 due to maternal hypertension with mild preeclampsia, birth weight 2910 g, length 47 cm. Polyhydramnios was detected at the end of the pregnancy. She had persistent ductus arteriosus (PDA), a small muscular-type ventricle septal defect (VSD) and coarctation of the aorta. The coarctatio aortae was resected at age 6 weeks, and at the same time the PDA was ligated. She has always been short statured: At age 4 months her length was 57 cm (1 cm below 2.5th centile), at age 2 1/2 years 81 cm (4 cm below 2.5th centile). Head circumferences were about 1 cm below the 2.5th centile, e.g. 46 cm at age 2 1/2 years. Major feeding difficulties necessitated gastrostomy at age 4 months. At current age (2 years and 10 months) she still has no interest for food and vomits easily, but feeding her through the enteral feeding tube (Mic-Key®) keeps her weight within normal range. On barium-contrast X-ray examination of the esophagus, peristalsis appeared normal without signs of gastro-esophageal reflux. A 24-hour esophageal pH-measurement also gave no indications of reflux. There has been clear psychomotor delay: She started to walk without support at age 2 years and has delayed language development, e.g. at age 2 1/2 years she spoke only 8–10 words but managed quite well by sign language. On neurological examination mirror movements of her hands were found. She also has hearing loss, already suspected before age 2 months and confirmed by brain stem audiometry at age 4 months. On CT-examination of the temporal bone, atretic auditory canals and no middle ear cavities were found. There is marked facial dysmorphism with high frontal hairline, low-set and posteriorly rotated small ears with crumpled helices, inverted epicanthus, short and down-slanting palpebral fissures, no visible eyelashes on lower eyelids, broad nasal root, thin upper lip, small chin and a short neck (Figure 1). A transverse palmar crease was found in the right hand, and on the inside of the left thigh brownish longitudinal streaks were seen. The right foot was deformed with the 1st toe bent in under the 2nd toe (Figure 1). On ophthalmological examination in narcosis, the optic papillae were grayish, and there were some granulations of the retinae in the macular areas. At present, she is an active girl that likes to play. Her only medication is for asthma.
Figure 1

The child with double tetrasomy 8+18 mosaicism at age 7 weeks (panels A-C) and age 1 year (panels D-E).

Results and Discussion

Because the girl was dysmorphic with major feeding difficulties, blood samples were drawn two days after birth for chromosome investigations; routine G-banding and chromosome-based high-resolution comparative genomic hybridization (HR-CGH). The G-banded karyotype, based on screening of ten metaphases from a phytohemagglutinin-stimulated 3-day blood lymphocyte cultures, was normal. Surprisingly, the HR-CGH result that came a few weeks later suggested a combination of non-mosaic trisomy 8 and trisomy 18 (Figure 2, panel A). An identical finding was subsequently done on a 3500 BAC-clone array-CGH platform made by the Norwegian Microarray Consortium (for details, see [9]), the ratio still indicating a 50% increase in DNA amount corresponding to chromosomes 8 and 18 (Figure 2, panel B). To investigate if uniparental disomy of other chromosomes might be present, or if abnormal copy number variants below the resolution limit of the 3500 BAC-clone array might be found, we have recently examined DNA from the child's original blood sample (taken at age 2 days) on the Affymetrix Genome-Wide Human SNP Assay Kit version 6.0 (Affymetrix, Inc., CA). No indication of uniparental disomy (i.e. larger regions of homozygocity) was found, and no additional (and structural) de novo copy number abnormalities were detected.
Figure 2

Chromosome-based high-resolution CGH result (panel A) and 1 Mb BAC-array CGH result (panel B) on a blood DNA sample collected at age two days. The apparent 50% increase in DNA amount corresponding to chromosomes 8 and 18 was due to double tetrasomy of both chromosomes (panel C, showing a double tetrasomic metaphase). By interphase FISH, four copies of chromosomes 8 and 18 were detected in 15% of the cells from a 3-days PHA-stimulated blood culture (panel D).

A re-examination of the original leukocyte cell culture suspension with FISH-probes for centromeres 8 and 18 explained the surprising CGH finding: In 2% of the metaphases (100 metaphases examined) and 15% of the interphases (200 nuclei examined) tetrasomy for both chromosomes were found (Figure 2, panels C and D). The discrepancy between the CGH-findings (50% dose increase for 8 and 18, suggesting that 50% of the cells had four chromosomes 8 and 18) and the cell culture findings (15% of the interphases had four chromosomes 8 and 18) were likely due to negative selection of double tetrasomic cells during PHA-stimulated culturing of blood leukocytes. This illustrates that conventional G-banded karyotyping may easily overlook such mosaicism. To investigate other tissues for similar mosaicism, a skin biopsy from the inside of the left thigh was collected for fibroblast culturing at age 4 months, and at age 14 months a buccal smear was collected. In none of these tissues double tetrasomic cells were found by interphase centromere 8+18 FISH with 200 nuclei examined in each case. At age 20 months, a new blood sample was taken, and the double tetrasomic cells could no longer be detected, neither by CGH nor by interphase FISH.

To determine the origin of the four extra chromosomes (two chromosomes 8 and two chromosomes 18) that probably were present in around 50% of the blood leukocytes at the time of birth, microsatellite markers for chromosomes 8 and 18 were compared between blood-DNA samples from the parents and the original child blood-DNA sample taken at age 2 days (Table 1). There was no indication of more than two alleles for any simple tandem repeat examined, making meiotic non-disjunction an unlikely mechanism. Furthermore, there was no systematic skewing of the ratios between maternal and paternal allele peak sizes (Table 1), which would have been the case if three of the chromosomes in each quadruple were uniparental. Taken together, this indicates that the mosaicism was a consequence of mitotic events, and that the origin is a mitotic division where all four chromatids of two chromosome pairs (8 and 18) segregated to one daughter cell only.
Table 1

Allele sizes of polymorphic chromosome 8 and18 simple tandem repeats.

UniSTS

Position (Mb from pter)

Mother (m)

Father (p)

Child

Ratio m/p peak heights

Chrom. 8:

     

D8S264

21

153–155

143–153

143–155

0,50

D8S1104

41

135–135

143-143

135–143

1,01

D8S268

41

260–266

264–266

260–264

1,24

D8S531

49

121–127

123-123

121–123

1,60

G08718

49

219-219

214-214

214–219

0,94

D8S517

53

251–253

255–258

251–255

1,37

D8S260

62

207–215

209–215

207–215

1,05

D8S277

65

165–173

165–169

169–173

1,18

D8S270

93

101–112

110–112

101–110

1,84

D8S1784

106

288-288

282–286

282–288

0,71

D8S550

109

194–212

210-210

210–212

0,65

     

Mean 1,03

Chrom. 18:

     

D18S452

6

128–144

132–136

136–144

1,00

D18S53

11

165–173

165–169

169–173

1,19

D18S453

13

148–152

152-152

148–152

2,13

D18S71

13

270–278

258–276

258–278

0,55

D18S73

13

142–144

142–146

144–146

1,98

D18S1104

17

148–152

141–148

141–148

1,10

D18S1149

17

258–265

263–267

263–265

0,77

D18S869

18

186–198

186–189

186–198

1,39

D18S478

23

248–250

246-246

246–250

1,21

D18S1102

33

90–94

90–92

90–94

0,97

D18S474

47

124–126

132–138

126–138

2,68

D18S61

66

228–230

232-232

228–232

2,13

D18S1161

70

231–233

219-219

219–233

0,79

     

Mean 1,24

The ratio between the maternal and paternal peak heights is given in the right column, with the geometrical means of each chromosome in bold. The names of the centromeric repeats are written in italics.

The finding of tetrasomy for two autosomes in a newborn is without precedence. To the best of our knowledge, even single chromosome tetrasomy mosaicism has not previously been reported – except in cancer cells. The reason for the uniqueness of our finding is either that this indeed is a very rare chromosomal aberration, or that this type of malsegregation commonly occurs but is not detected due to negative selection against aneuploid cells during embryonic development and the culturing of blood cells for routine karyotyping. We were fortunate to observe this because we performed "unbiased" CGH analyses on leukocyte DNA from a newborn. Moreover, extra copies of both of the involved chromosomes are known to be compatible with sustained cell growth in the embryo, increasing the likelihood that a double tetrasomic cell line could survive to term. Notably, the initial cytogenetic investigation (G-banding) appeared normal – only a later reexamination by FISH revealed double tetrasomic cells and metaphases (Figure 2). Apparently, the short-term PHA-stimulated leukocyte culture decreased the number of aberrant cells from around 50% to 15%. Twenty months later the aberrant clone was undetectable in blood, probably because it was counter-selected in the bone marrow.

At a later time point we were unsuccessful in finding double tetrasomic cells in other tissues, i.e. in squamous epithelial cells from a buccal smear and cultivated fibroblasts from a skin biopsy taken from left groin, where skin pigment mosaicism could be seen. The reason for this, at least when the fibroblasts are concerned, can be the unpredictable distribution of mosaicism and not necessarily a negative selection process [10]. Even though we lack cytogenetic proof that the mosaicism affects other tissues than the bone marrow, the clinical picture suggests this. The child's phenotype has elements of resemblance to children with mosaicism for trisomy 8 or trisomy 18 (Table 2). In fact, there are no known physical features in the patient, with the possible exception of poorly developed lower eyelashes, that has not been reported in patients with trisomy 8 or 18 mosaicism [1113].
Table 2

The patient's phenotypic features compared to cases with mosaic trisomy 8 or 18

Our patient: Double tetrasomy 8+18 mosaicism

Trisomy 8

mosaicism

Trisomy 18

mosaicism

Short stature

 

+

Small head

+

+

Feeding problems

 

+

Developmental delay

+

+

Deafness, conductive

+

 

High frontal hairline/prominent forehead

+

+

Low-set/posteriorly rotated ears

+

+

Crumpled ear helices

 

+

Narrow/atretic auditory canals

+

 

Middle ear abnormalities

 

+

Short palpebral fissures

 

+

Epicantic folds

 

+

Downslant

+

 

Broad nasal bridge

+

+

Thin upper lip

 

+

Small chin

+

+

Short neck

+

+

Skin pigmentation anomalies

+

 

Overriding toes

 

+

Coarctatio aortae

 

+

Ventricular septal defect (VSD)

+

+

Persistent ductus arteriosus (PDA)

+

+

Retinitis pigment.-like findings in retina

+

 

This case is of particular interest because it illuminates early events in embryogenesis that may have implications for tumor biology. Our data suggests that all four chromatids of the homologous pair were pulled to one daughter cell only by the mitotic spindle apparatus, analogous to the syntelic attachment of the mitotic spindle that may be seen in tetraploid yeast cells [5]. Unlike other organisms, pairing of homologous chromosomes in somatic cells is commonly seen in Dipterians such as Drosophila and mosquitoes [14]. Notably, homologous pairing in both meiosis and mitosis occurs independently of synapsis and recombination [14]. Furthermore, the finding of (mosaic) segmental isodisomy as a disease mechanism in some cases of imprinting-related growth syndromes (e.g. Beckwith-Wiedemann syndrome and Russell-Silver syndrome, [15]) also indicates that mitotic homologous pairing takes place. That such pairing is not limited to imprinted chromosomes are illustrated by the reports of children with recessive diseases due to homozygocity for mutations carried by one of the parents only, the disease manifesting due to segmental isodisomy formation [1619].

We believe that the most likely explanation for the double tetrasomy is that the starting point was a tetraploid state, which is the normal situation after S-phase, or a tetraploid cell line. If the origin was a tetraploid state, aborted S-phase (mitotic slippage) or interrupted M-phase (failed cytokinesis) are possible mechanisms. Chromatid non-disjunction is one suggested reason for failed cytokinesis [6, 8]. If the origin was a tetraploid cell line, there are scant indications that such cells may later become diploid. In Candida albicans tetraploid strains become diploid or near diploid through "concerted chromosome loss" [20]. In hepatic cells being tetraploid after fusion to bone marrow stem cells, a "reduction mitosis" appears to be able to transform tetraploid hybrids into diploids [21]. In both cases the mechanism is unknown. A variable number of tetraploid cells is commonly found in chorion villus or amniocyte cultures, but such cells are rarely found in liveborns [22]. The origin can be meiotic or mitotic errors [23, 24].

Conceivably, failed cytokinesis or mitotic slippage might be quite common events in early embryogenesis, for instance during the rapid cell cycles taking place in the peri-gastrulation stage of mammalian embryogenesis [25]. If there exists a special mechanism to deal with this, e.g. to reinitiate the spindle apparatus after the failure has been corrected, balanced segregation would be an advantage, and this could require pairing of the homologues. A further hypothetical advantage of such pairing is removal of replication errors or detrimental mutations from at least one of the daughter cells by segregating both chromatids of one homologous pair to the same daughter cell, if necessary after mitotic crossovers. In the latter case uniparental isodisomy (UPD) for the whole or a segment of a chromosome would be the result. Our hypothesis is illustrated in Figure 3, modeling single chromosome aneuploidy due to chromatid non-disjunction and double chromosome aneuploidy caused by paired homologues non-disjunction.
Figure 3

A drawing that exemplifies the hypothesized mitotic homologue non-disjunction. The upper part of the figure shows two separate homologue pairs from a conventional mitosis, and in one chromosome a chromatid non-disjunction occurs. The lower part of the figure illustrates two pairs of homologues from a mitosis where pairing has occurred between all homologue chromosomes, and where all (four) chromatids of one such pair segregates to the same daughter cell. We suggest that this might have happened very early in development to two homologue pairs, made by chromosomes 8 and 18. We also illustrate how a detrimental mutation that has arisen during replication (marked by an asterix) may be eliminated by segregation to one daughter cell only after a mitotic cross-over that also generates a segmental (and terminal) uniparental isodisomy.

Conclusion

This unique case indirectly suggests that a mechanism for tetraploidy correction involving pairing of homologues may be present in somatic cells, and that mosaicism originating in tetraploidization could be a cause of developmental abnormalities that usually remain undetected. When such a mechanism is dysfunctional, aneuploidy is a likely result – which is commonly found in many types of cancer.

Consent

The parents have given written consent to publication of the patient's pictures, and the parents have also seen and approved the publication of the disease history.

Declarations

Acknowledgements

The scientific discussion and review of the manuscript by Helge Boman and Anders Molven was highly appreciated. Noralv Breivik has provided additional clinical information. Most of the laboratory work has been done in the diagnostic DNA and cytogenetic laboratories at Haukeland University Hospital, lead by Hanne M. Jacobsen and Kjetil Solland. This work could not have been done without the collaboration of the child's parents, to whom we are most grateful.

Authors’ Affiliations

(1)
Center for Medical Genetics and Molecular Medicine, Haukeland University Hospital
(2)
Department of Clinical Medicine, University of Bergen
(3)
Department of Pediatrics, Ålesund Hospital

References

  1. Micale MA, Wolff DJ, Dickerman LH, Redline R, Conroy JM, Schwartz S: Cytogenetic and molecular genetic characterization of trisomy 20 mosaicism in fetal blood and tissues. Prenat Diagn. 1996, 16 (10): 893-897. 10.1002/(SICI)1097-0223(199610)16:10<893::AID-PD962>3.0.CO;2-M.View ArticlePubMedGoogle Scholar
  2. Karadima G, Bugge M, Nicolaidis P, Vassilopoulos D, Avramopoulos D, Grigoriadou M, Albrecht B, Passarge E, Anneren G, Blennow E, et al: Origin of nondisjunction in trisomy 8 and trisomy 8 mosaicism. Eur J Hum Genet. 1998, 6 (5): 432-438. 10.1038/sj.ejhg.5200212.View ArticlePubMedGoogle Scholar
  3. Callier P, Faivre L, Cusin V, Marle N, Thauvin-Robinet C, Sandre D, Rousseau T, Sagot P, Lacombe E, Faber V, et al: Microcephaly is not mandatory for the diagnosis of mosaic variegated aneuploidy syndrome. Am J Med Genet A. 2005, 137 (2): 204-207.View ArticlePubMedGoogle Scholar
  4. Hanks S, Coleman K, Reid S, Plaja A, Firth H, Fitzpatrick D, Kidd A, Mehes K, Nash R, Robin N, et al: Constitutional aneuploidy and cancer predisposition caused by biallelic mutations in BUB1B. Nat Genet. 2004, 36 (11): 1159-1161. 10.1038/ng1449.View ArticlePubMedGoogle Scholar
  5. Ganem NJ, Storchova Z, Pellman D: Tetraploidy, aneuploidy and cancer. Curr Opin Genet Dev. 2007, 17 (2): 157-162. 10.1016/j.gde.2007.02.011.View ArticlePubMedGoogle Scholar
  6. Fujiwara T, Bandi M, Nitta M, Ivanova EV, Bronson RT, Pellman D: Cytokinesis failure generating tetraploids promotes tumorigenesis in p53-null cells. Nature. 2005, 437 (7061): 1043-1047. 10.1038/nature04217.View ArticlePubMedGoogle Scholar
  7. Weaver BA, Silk AD, Cleveland DW: Cell biology: nondisjunction, aneuploidy and tetraploidy. Nature. 2006, 442 (7104): E9-10. 10.1038/nature05139. discussion E10View ArticlePubMedGoogle Scholar
  8. Shi Q, King RW: Chromosome nondisjunction yields tetraploid rather than aneuploid cells in human cell lines. Nature. 2005, 437 (7061): 1038-1042. 10.1038/nature03958.View ArticlePubMedGoogle Scholar
  9. Lybaek H, Meza-Zepeda LA, Kresse SH, Hoysaeter T, Steen VM, Houge G: Array-CGH fine mapping of minor and cryptic HR-CGH detected genomic imbalances in 80 out of 590 patients with abnormal development. Eur J Human Genet. 2008, 16 (11): 1318-1328. 10.1038/ejhg.2008.78.View ArticleGoogle Scholar
  10. Houge G, Boman H, Lybaek H, Ness GO, Juliusson PB: Lack of meiotic crossovers during oogenesis in an apparent 45, X Ullrich-Turner syndrome patient with three children. Am J Med Genet A. 2006, 140 (10): 1092-1097.View ArticlePubMedGoogle Scholar
  11. Tucker ME, Garringer HJ, Weaver DD: Phenotypic spectrum of mosaic trisomy 18: two new patients, a literature review, and counseling issues. Am J Med Genet A. 2007, 143 (5): 505-517.View ArticleGoogle Scholar
  12. Su PH, Chen JY, Hsu CH, Chen SJ, Chan SW, Lin LL: Trisomy 18 with multiple rare malformations: report of one case. Acta Paediatr Taiwan. 2007, 48 (5): 272-275.PubMedGoogle Scholar
  13. Schinzel A: Catalogue of Unbalanced Chromosome Aberrations in Man. 2001, Berlin; New York: Walter de Gruyter, 2Google Scholar
  14. McKee BD: Homologous pairing and chromosome dynamics in meiosis and mitosis. Biochim Biophys Acta. 2004, 1677 (1–3): 165-180.View ArticlePubMedGoogle Scholar
  15. Cooper WN, Curley R, Macdonald F, Maher ER: Mitotic recombination and uniparental disomy in Beckwith-Wiedemann syndrome. Genomics. 2007, 89 (5): 613-617. 10.1016/j.ygeno.2007.01.005.View ArticlePubMedGoogle Scholar
  16. Kotzot D: Complex and Segmental Uniparental Disomy (UPD) Updated. J Med Genet. 2008, 45 (9): 545-556. 10.1136/jmg.2008.058016.View ArticlePubMedGoogle Scholar
  17. Spiekerkoetter U, Eeds A, Yue Z, Haines J, Strauss AW, Summar M: Uniparental disomy of chromosome 2 resulting in lethal trifunctional protein deficiency due to homozygous alpha-subunit mutations. Hum Mutat. 2002, 20 (6): 447-451. 10.1002/humu.10142.View ArticlePubMedGoogle Scholar
  18. Chevalier-Porst F, Rolland MO, Cochat P, Bozon D: Maternal isodisomy of the telomeric end of chromosome 2 is responsible for a case of primary hyperoxaluria type 1. Am J Med Genet A. 2005, 132A (1): 80-83. 10.1002/ajmg.a.30375.View ArticlePubMedGoogle Scholar
  19. van Riesen AK, Antonicka H, Ohlenbusch A, Shoubridge EA, Wilichowski EK: Maternal segmental disomy in Leigh syndrome with cytochrome c oxidase deficiency caused by homozygous SURF1 mutation. Neuropediatrics. 2006, 37 (2): 88-94. 10.1055/s-2006-924227.View ArticlePubMedGoogle Scholar
  20. Bennett RJ, Johnson AD: Completion of a parasexual cycle in Candida albicans by induced chromosome loss in tetraploid strains. Embo J. 2003, 22 (10): 2505-2515. 10.1093/emboj/cdg235.View ArticlePubMedPubMed CentralGoogle Scholar
  21. Wang X, Willenbring H, Akkari Y, Torimaru Y, Foster M, Al-Dhalimy M, Lagasse E, Finegold M, Olson S, Grompe M: Cell fusion is the principal source of bone-marrow-derived hepatocytes. Nature. 2003, 422 (6934): 897-901. 10.1038/nature01531.View ArticlePubMedGoogle Scholar
  22. Schluth C, Doray B, Girard-Lemaire F, Favre R, Flori J, Gasser B, Rudolf G, Flori E: Prenatal diagnosis of a true fetal tetraploidy in direct and cultured chorionic villi. Genet Couns. 2004, 15 (4): 429-436.PubMedGoogle Scholar
  23. Guc-Scekic M, Milasin J, Stevanovic M, Stojanov LJ, Djordjevic M: Tetraploidy in a 26-month-old girl (cytogenetic and molecular studies). Clin Genet. 2002, 61 (1): 62-65. 10.1034/j.1399-0004.2002.610112.x.View ArticlePubMedGoogle Scholar
  24. Nakamura Y, Takaira M, Sato E, Kawano K, Miyoshi O, Niikawa N: A tetraploid liveborn neonate: cytogenetic and autopsy findings. Arch Pathol Lab Med. 2003, 127 (12): 1612-1614.PubMedGoogle Scholar
  25. O'Farrell PH, Stumpff J, Su TT: Embryonic cleavage cycles: how is a mouse like a fly?. Curr Biol. 2004, 14 (1): R35-45.View ArticlePubMedPubMed CentralGoogle Scholar
  26. Pre-publication history

    1. The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2350/10/42/prepub

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