A case report of Pallister-Killian syndrome with an unusual mosaic supernumerary marker chromosome 12 with interstitial 12p13.1-p12.1 duplication

Abstract

Pallister-Killian syndrome (PKS) is a rare inherited disease with multiple congenital anomalies, profound intellectual disability, and the presence in the karyotype of sSMC - i(12)(p10). The frequency of PKS may be underestimated due to problems with cytogenetic diagnosis caused by tissue-specific mosaicism and usually a low percentage of peripheral blood cells containing sSMC. Such tissue-specific mosaicism also complicates a detailed analysis of the sSMC, which, along with the assessment of mosaicism in different tissues, is an important part of cytogenetic diagnosis in PKS. Unfortunately, a full-fledged diagnosis in PKS is either practically impossible or complicated. On the one hand, this is due to problems with the biopsy of various tissues (skin biopsy with fibroblast culture is most often used in practice); on the other - a low percentage of dividing peripheral blood cells containing sSMC, which often significantly complicates the analysis of its composition and organization. In the present study, a detailed analysis of sSMC was carried out in a patient with a characteristic clinical picture of PKS. A relatively high percentage of peripheral blood cells with sSMC (50%) made it possible to perform a detailed molecular cytogenetic analysis of de novo sSMC using chromosomal in situ suppression hybridization (CISS-hybridization), multicolor FISH (mFISH), multicolor chromosome banding (MCB), array CGH (aCGH), and quantitative real-time PCR (qPCR), and short tandem repeat (STR) - analysis. As a result, it was found that the sSMC is not a typical PKS derivative of chromosome 12. In contrast to the classical i(12)(p10) for PKS, the patient's cells contained an acrocentric chromosome consisting of 12p material. Clusters of telomeric repeats were found at the both ends of the sSMC. Furthemore, the results of aCGH and qPCR indicate the presence of interstitial 8.9 Mb duplication at 12p13.1-p12.1 within the sSMC, which leads to different representations of DNA from different segments of 12p within cells containing sSMC. The obtained data raise the question of the instability of the sSMC and, as a consequence, the possible presence of additional rearrangements, which, in traditional cytogenetic analysis of patients with PKS, are usually described as i(12)(p10).

Keywords: Pallister-Killian syndrome (PKS); a supernumerary marker of chromosome 12; chromosomal abnormalities; duplication 12p13.33-p11.1; mosaic trisomy 12p; the chromosomal region 12pter-12q11.

FIGURE 1

The patient at the ages of 4 months (A), 1 year and 9 months (B) and 6 years with mother (C).

FIGURE 2

GTG-banded patient’s chromosomes. Arrow points to the sSMC.

FIGURE 3

24-color FISH with the patient’s metaphase chromosomes.

FIGURE 4

Result of high-resolution multicolor banding (MCB) after application of a chromosome 12 specific probe cocktail. (A) The resulting pseudocolor MCB patterns for the two normal chromosomes 12 and the derivative chromosome 12 (mar) of the presented PKS patient. The arrow points to the small supernumerary marker chromosome 12. (B) The localization of the chromosome 12 region-specific partial chromosome paints and the used fluorochromes are shown. At the bottom are the intensity profiles. The red line on chromosome 12 and the marker is the line along which the intensity profiles were measured. (C) MCB of a chromosome 12 and marker are presented. Scale bar 50 µm.

FIGURE 5

Fluorescence in situ hybridization of (A) the telomeric (red) and (B) the pan-centromeric (red) probes and PCP12-2 probe labeled with AlexaFluor488-5-dUTP (green) on metaphase chromosomes in peripheral blood lymphocytes of patient. The total number of chromosomes is 47. The arrow points to the small supernumerary marker chromosome 12 found in the patient’s karyotype. Scale bar 50 µm.

FIGURE 6

qPCR-validation of mosaicism level for sSMC(12) in a patient with PKS. Footnote. C–control DNA with normal karyotype (Agilent Technologies, United States); PC–positive control–DNA of a patient with dup12p13.31; PC mos–DNA of a patient with dup12p13.31 mixed with control DNA in a 1:1 ratio to model 50% mosaicism at the locus of interest; Patient - DNA of analyzed patient.

FIGURE 7

The aCGH profile of chromosome 12 with 12p13.33→p11.1 duplication for proband (A) and his mother (B).

FIGURE 8

Familial analysis of chromosome 12 inheritance by STR genotyping.

FIGURE 9

qPCR-validation of mosaicism level for sSMC(12) in a patient with Pallister-Killian syndrome. Footnote. Trisomy 12–DNA from cells of extraembryonic tissues of spontaneous abortion with trisomy 12, Triomy 12 (50% mosaicism)–DNA from cells of extraembryonic tissues of spontaneous abortion with trisomy 12 and control DNA from cells with normal karyotype in a 1:1 ratio.

FIGURE 10

Suppression fluorescence in situ hybridization of locus-specific DNA probes on the patient’s metaphase chromosomes. FISH TEL/AML1 Translation, Dual Fusion Probe (Cytocell, Cambridge, UK). TEL (12p13.2)–red, AML1 (21q22.12)–green. Chromosome 12 and marker 12, bearing a red signal in the 12p13.2 locus, and their inverted DAPI banding are shown at the bottom left. The arrow points to the small supernumerary marker chromosome 12 found in the patient’s karyotype. General chromosome staining with DAPI (blue signal). Scale bar 50 µm.

FIGURE 11

Mapping of candidate genes of structural brain abnormalities in patients with PKS. The figure is based and modified from the original map by Poulton et al. (2018) (Poulton et al., 2018). Blue dotted lines are the boundaries of localization of genes associated with abnormalities of corpus collosum and white matter (left) and macrocephaly (right). Green dotted lines are the boundaries of duplicated 12p13.1-p12.1 region (shown in black) within the sSMC(12) (shown in grey) in our patient.