8p23.1 duplication syndrome differentiated from copy number variation of the defensin cluster at prenatal diagnosis in four new families

Abstract

Background: The 8p23.1 duplication syndrome and copy number variation of the 8p23.1 defensin gene cluster are cytogenetically indistinguishable but distinct at the molecular level. To our knowledge, the 8p23.1 duplication syndrome has been described at prenatal diagnosis only once and we report our experience with four further apparent duplications ascertained at prenatal diagnosis.

Methods: Additional material at band 8p23.1 was detected using conventional G-banded cytogenetics in each case. Multiplex Ligation-dependent Probe Amplification (MLPA) or Fluorescence In Situ Hybridisation (FISH) were used depending on whether only DNA (Cases 1 and 4) or cytogenetic preparations (Cases 2 and 3) were available from the laboratory of origin. The extent of the duplication in Case 1 was retrospectively determined using array Comparative Genomic Hybridisation (array CGH).

Results: Three cases of 8p23.1 duplication syndrome were found (Cases 1 to 3). Two were de novo and continued to term and the third, a paternally transmitted duplication, was terminated because of a previous child with psychomotor delay and 8p23.1 duplication syndrome. Case 1 was ascertained with a hypoplastic left heart but the ventricular septal and interventricular defects, in Cases 2 and 3 respectively, were found after ascertainment for advanced maternal age. By contrast, case 4 was a maternally transmitted copy number variation of the defensin cluster with normal outcome.

Conclusions: Our data underline the need to differentiate 8p23.1 duplications from copy number variation of the defensin cluster using FISH, MLPA or array CGH. Cardiac defects were ascertained by ultrasound in only one of the three duplication 8p23.1 pregnancies but were visible in two of the three at 21 to 22 weeks gestation. Our results provide further evidence that both deletion and duplication of the GATA4 transcription factor can give rise to a variety of conotruncal heart defects with variable penetrance and expressivity.

Figure 1

G-banded partial karyotypes (A-F). (A) Case 1, (B) Case 2, (C) the Case 3 proband, (D) the father of the proband, (E) the elder sister of the proband and (F) Case 4. The duplicated or variant chromosome is on the right hand side of each chromosome pair and the expanded G-light region of 8p23.1 indicated by the black arrow in each case. Note the similarity of the G-banded copy number variant 8 in Case 4 to the duplicated 8 s in the probands of Cases 1 to 3.

Figure 2

Molecular cytogenetic results in Cases 1 to 3. Case 1 (A): The BAC array CGH result, which confirmed the MLPA findings, displayed with BlueFuse software and showing the region of copy number gain at 8p23.1 (green bar to the right of the idiogram); Case 2 (B-E): (B) the larger metaphase signals (arrowed) from the 8p23.1 BACs RP11-211C9 (red) and RP11-589N15 (green) and (C) the enhanced signal strength from BAC RP11-211C9 (red) at metaphase (single red arrow) and the duplicated signals at interphase (double red arrows) (note, the green signals are from BAC CTD-2629I168 and the 8 centromere which both had normal copy number); (D) the normal results from BAC RP11-594D21 (red) in distal REPD and a control BAC RP11-410N18 from 8p23.3 (green); (E, left hand pairs) the duplicated signals (vertical arrows) from BACs RP11-351I21 (red) in REPP and RP11-1118M6 (green) in REPD from the fetus and (E, right hand pairs) the normal copy in the mother. Case 3 (F-H): (F) the enhanced metaphase signal strength (red and green arrows) from the REPD BACs RP11-122N11 (red) and RP11-589N15 (green) note, (the additional red signals are from the 8 centromere); (G) the duplicated metaphase signals (single green arrow) from BAC RP11-211C9 (green) and (H) at prometaphase (red and green arrows) from BAC RP11-24D9 (red) in REPP from BAC RP11-589N15 (green).

Figure 3

Annotated screenshot of 5.7 Mb of band 8p23.1 (UCSC Genome Browser on Human Mar. 2006 Assembly (hg18)). From bottom to top: the Segmental Duplications that contain the Olfactory Receptor and Defensin Repeats (ORDRs) are labelled REPD and REPP; the ~3.75 Mb core 8p23.1 duplication syndrome interval between REPD and REPP [5] and the ~2.5 Mb alternative CHD region proposed by Giglio et al [24] are illustrated by annotated boxes; the multiple copy number variations of REPD and REPP in the Database of Genome Variants (DGV) http://projects.tcag.ca/variation/ is indicated by the red, blue and green lines and the common polymorphic inversion between REPD and REPP by the purple lines; OMIM Morbid genes appear as red boxes and other OMIM genes as blue boxes (or lines); acronyms for the OMIM genes specifically mentioned in the text have been added above in corresponding colours. Note that the DGV does not contain any CNVs that match the 8p23.1 duplication syndrome region.