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BRIEF REPORT

Three Cases with Enlarged Acrocentric p-arms and Two Cases with Cryptic Partial Trisomies

Heike Starke, Kristin Mrasek and Thomas Liehr

Institute of Human Genetics and Anthropology, Jena, Germany

Correspondence to: Dr. Thomas Liehr, Institut für Humangenetik und Anthroplogie, Kollegiengasse 10, D-07743 Jena, Germany. E-mail: i8lith{at}mti.uni-jena.de


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In three cases, banding analysis revealed a normal karyotype except for an enlarged short arm of one chromosome 13 or 15. To clarify whether this enlargement was due to a heteromorphism or to a cryptic chromosomal trisomy, so-called cenM-FISH probe sets containing a microdissection-derived probe specific for the acrocentric human p-arms were applied. The results enabled us to confirm in one case and to exclude in two cases that the enlargement on the suspect chromosome was due to a p-arm polymorphism. M-FISH and/or microdissection were used to resolve the nature of the rearrangements, i.e., partial trisomies 6 and 19. (J Histochem Cytochem 53:359–360, 2005)

Key Words: prenatal diagnosis • acrocentric chromosomes • p-arms • FISH • heteromorphism • cryptic trisomy

WHEN an enlarged short arm of one of the acrocentric chromosomes (13, 14, 15, 21, and 22) is detected during karyotyping, the cytogeneticist must clarify whether this is due to an unusual variant or whether it masks a translocation event. Detection of such a p-arm variant is routinely followed by CBG and NOR staining and by karyotypic analysis of the parental chromosomes (Wyandt and Tonk 2004Go). Even though this usually leads to an informative result (Alitalo et al. 1988Go; Schmid et al. 1994Go; Reddy and Sulcova 1998Go; Wyandt and Tonk 2004Go) FISH (fluorescence in situ hybridization) techniques were introduced during the past decade to address that problem in more detail (e.g., Verma et al. 1996Go). Especially for cases in which the p-arm enlargement hides a cryptic (euchromatic) rearrangement, molecular cytogenetics is crucial to characterize the chromosomal imbalance in detail (e.g., Morelli et al. 1999Go; Benzacken et al. 2001Go; Trifonov et al. 2003Go).

Here we report on three cases with an enlarged p-arm in chromosome 13 (case 2 and 3) or 15 (case 1). Cases 1 and 3 were postnatal cases; case 3 was prenatal. Case 1 was a healthy adult male whose partner had a history of several abortions. Case 2 had a white spot detected in prenatal ultrasound screening. Case 3 was 2 years old and exhibited developmental delay, short stature, and several dysmorphic signs including blepharophimosis, high-arched palate, hypolastic philtrum, low-set ears, and microcephaly.

For cases 1 and 2 we applied the corresponding subcenM-FISH probe sets (Starke et al. 2003Go), and for case 3 the recently described acrocenM-FISH probe set (Trifonov et al. 2003Go). Both probe sets contain the microdissection-derived probe midi54 specific for the short arm of all human acrocentric chromosomes (Mrasek et al. 2001Go), which is essential for the characterization of p-arm heterochromatin presence or absence.

For case 1, the FISH result with the midi54 probe showed that the entire enlarged short arm consisted exclusively of heterochromatic material (Figure 1). Therefore, a balanced translocation was excluded as a reason for abortions in that family, although the large p-arm in one chromosome 15 could not be excluded as connection to that problem (i.e., mitotic problems during embryogenesis). Similar cases with such large p-arm variants and without phenotypic consequences were described previously (Wyandt and Tonk 2004Go). Especially for chromosome 15 p-arm variants, the possibility of a der(15)t(Y;15)(q12q11.2) must be considered (Alitalo et al. 1988Go; Wyandt and Tonk 2004Go).



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Figures 1–3

Figure 1 Pair of chromosomes 15 as visible for case 1: an enlarged p-arm was detected after banding cytogenetics (arrowhead), which was completely stained by a probe specific for all acrocentric human p-arms (midi54). A three-color depiction of the subcenM-FISH result (for method see Starke et al. 2003Go) of the chromosome 15-specific probe set is depicted as inverted DAPI (left) and as true-color image for the centromere-specific (cep), the whole chromosome painting (wcp), and the midi54 probe (right). The FISH result of the centromere-near probe enclosed in the subcenM-FISH probe set is not shown because it does not provide any additional information.

Figure 2 For case 2 a chromosome 13p+ (arrowhead) was found during karyotyping. Inverted DAPI and subcenM-FISH results are depicted on the left part of the figure (as in Figure 1). The arrowhead in the subcenM-FISH figure points to the unstained region of the p-arm in question. The latter was proved to be a part of chromosome 19 by M-FISH (result not shown) and a whole chromosome paint 19 (result shown on the right).

Figure 3 The chromosomes 13p+ of case 3 (arrowhead) was characterized by glass needle-based microdissection as a material derived from chromosome 6p22.2-pter. Inverted DAPI banding of the chromosome 13 pair and a partial metaphase after reverse painting with the microdissected probe are shown.

 
In cases 2 and 3 the probe midi54 did not stain the entire enlarged short p-arm of the corresponding chromosomes 13 in question (see Figure 2 for case 2; for case 3 see Trifonov et al. 2003Go). This was a strong clue to the presence of euchromatic material of unknown origin on the derivative chromosomes. For case 2, an M-FISH experiment identified the additional material as being derived from chromosome 8, 19, or 21; a whole chromosome painting probe for chromosome 19 characterized the derivative chromosome 13 as a der(13)t(13;19)(p11.2;p13.1 or q13.1) (Figure 2). The pregnancy was terminated and an autopsy was not performed. For case 3, M-FISH did not lead to informative results. Therefore, glass needle-based chromosome microdissection was performed. The result of the reverse FISH experiment is shown in Figure 3. Apart from the enlarged short arm of chromosome 13 and the short arms of the other acrocentric chromosomes, the end of chromosome 6p was specifically stained. Therefore, and confirmed by other FISH experiments (see Trifonov et al. 2003Go), it could be deduced that a partial trisomy 6p22.2-pter was present.

In summary, it can be assumed that every acrocentric short arm marker of which the size appears abnormally large should be studied in detail by different molecular cytogenetic methods such as M-FISH/SKY, microdissection, and reverse painting or cenM-FISH methods, including a probe such as midi54. In some cases the clinical phenotype may provide clues about the chromosomal region to look for (Benzacken et al. 2001Go), although in most cases, like those reported here, this advantage will not be present (Morelli et al. 1999Go; Trifonov et al. 2003Go).


    Acknowledgments
 
Supported in part by the EU (ICA2-CT-2000-10012) and by the Dr. Robert Pfleger Stiftung.

Cases were kindly provided by Dr Seidel (Jena), Dr Sandig (Weimar), and Dr Wegner (Berlin).


    Footnotes
 
Presented in part at the 14th Workshop on Fetal Cells and Fetal DNA: Recent Progress in Molecular Genetic and Cytogenetic Investigations for Early Prenatal and Postnatal Diagnosis, Friedrich Schiller University, Jena, Germany, April 17–18, 2004.

Received for publication May 18, 2004; accepted June 7, 2004


    Literature Cited
 Top
 Summary
 Literature Cited
 

Alitalo T, Tiihonen J, Hakola P, de la Chapelle A (1988) Molecular characterization of a Y;15 translocation segregating in a family. Hum Genet 79:29–35[CrossRef][Medline]

Benzacken B, Monier-Gavalle F, Siffroi JP, Agbo P, Chalvon A, Wolf JP (2001) Acrocentric chromosome polymorphisms: beware of cryptic translocations. Prenat Diagn 21:96–98[CrossRef][Medline]

Morelli SH, Deubler DA, Brothman LJ, Carey JC, Brothman AR (1999) Partial trisomy 17p detected by spectral karyotyping. Clin Genet 55:372–375[CrossRef][Medline]

Mrasek K, Heller A, Rubtsov N, Trifonov V, Starke H, Rocchi M, Claussen U, et al. (2001) Reconstruction of the female Gorilla gorilla karyotype using 25-color FISH and multicolor banding (MCB). Cytogenet Cell Genet 93:242–248[CrossRef][Medline]

Reddy KS, Sulcova V (1998) The mobile nature of acrocentric elements illustrated by three unusual chromosome variants. Hum Genet 102:653–662[CrossRef][Medline]

Schmid M, Nanda I, Steinlein C, Epplen JT (1994) Amplification of (GACA)n simple repeats in an exceptional 14p+ marker chromosome. Hum Genet 93:375–382[Medline]

Starke H, Nietzel A, Weise A, Heller A, Mrasek K, Belitz B, Kelbova C, et al. (2003) Small supernumerary marker chromosomes (SMCs): genotype-phenotype correlation and classification. Hum Genet 114:51–67[CrossRef][Medline]

Trifonov V, Seidel J, Starke H, Martina P, Beensen V, Ziegler M, Hartmann I, et al. (2003) Enlarged chromosome 13 p-arm hiding a cryptic partial trisomy 6p22.2-pter. Prenat Diagn 23:427–430[CrossRef][Medline]

Verma RS, Kleyman SM, Conte RA (1996) Molecular characterization of an unusual variant of the short arm of chromosome 15 by FISH-technique. Jpn J Hum Genet 41:307–311[Medline]

Wyandt HE, Tonk VS (2004) Atlas of Human Chromosome Heteromorphisms. Dordrecht, Boston, London, Kluwer Academic Publishers





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