Dysregulation of FOXG1 by ring chromosome 14

Abstract

In this study we performed molecular characterization of a patient with an extra ring chromosome derived from chromosome 14, with severe intellectual disability, epilepsy, cerebral paresis, tetraplegia, osteoporosis and severe thoraco-lumbal scoliosis. Array CGH analysis did not show any genomic imbalance but conventional karyotyping and FISH analysis revealed the presence of an interstitial 14q12q24.3 deletion and an extra ring chromosome derived from the deleted material. The deletion and ring chromosome breakpoints were identified at base-pair level by mate-pair and Sanger sequencing. Both breakpoints disrupted putative long non-coding RNA genes (TCONS00022561;RP11-148E17.1) of unknown function. However, the proximal breakpoint was 225 kb downstream of the forkhead box G1 gene (FOXG1), within the known regulatory landscape of FOXG1. The patient represents the first case of a r(14) arising from an interstitial excision where the phenotype is compatible with dysregulation of FOXG1. In turn, the phenotypic overlap between the present case, the FOXG1 syndrome and the r(14) syndrome supports that dysregulation of FOXG1 may contribute to the classical r(14)-syndrome, likely mediated by dynamic mosaicism.

Keywords: 14q12; Dynamic mosaicism; Epilepsy; FOXG1; Intellectual disability; Ring chromosome 14.

Figure 1

Chromosome analysis. a: Karyogram of the patient. b: Chromosome 14 and the r(14). Arrows on the left indicate the presumed position of the breakpoints. Arrow on the right side indicates the fusion of chromosome bands 14q12 and 14q24.3.

Figure 2

Molecular detection of the breakpoints. a: Schematic orientation of primers designed to amplify the breakpoints on the deleted and the ring chromosome 14. b: Agarose gel electrophoresis of PCR products obtained by primers D1-D3 and A1-A3. Specific amplifications (*) were observed at 62°C in patient (P) DNA but not in control (C) samples. NC: negative control. c: Mate-pair reads spanning the proximal and distal breakpoints, with resolutions corresponding to the shaded areas (proximal: ~1,000 bp; distal: ~330 bp). The thin grey lines indicate the position of the breakpoints as detected by Sanger sequencing. d: Position of BLAT sequences following Sanger sequencing, showing the location of the two breakpoints (upper arrows), the proximal two bp (CC) overlap and the distal 5 bp (GGGGC) deletion. e: Position of the proximal r(14) breakpoint in the highly conserved regulatory domain of FOXG1, proximal to the t(2;14)-breakpoint [13].

Figure 3

FISH analyses. a: The signals of BAC clone RP11-24K5 from the excised region are on the normal chromosome 14 and on the r(14). b: Absence of α-satellite DNA signal on the r(14).