Dezső David

Characterization of two ectrodactyly-associated translocation breakpoints separated by 2.5 Mb on chromosome 2q14.1–q14.2

Split hand-split foot malformation or ectrodactyly is a heterogeneous congenital defect of digit formation. The aim of this study is the mapping of the breakpoints and a detailed molecular characterization of the candidate genes for an isolated and syndromic form of ectrodactyly, both associated with de novo apparently balanced chromosome translocations involving the same chromosome 2 band, [t(2;11)(q14.2;q14.2)] and [t(2;4)(q14.1;q35)], respectively. Breakpoints were mapped by fluorescence in situ hybridization using bacterial artificial chromosome clones. Where possible, these breakpoints were further delimited. Candidate genes were screened for pathogenic mutations and the expression levels of two of them analysed. The isolated bilateral split foot malformation-associated chromosome 2 breakpoint was localized at 120.9 Mb, between the two main candidate genes, encoding GLI-Kruppel family member GLI2 and inhibin-βB. The second breakpoint associated with holoprosencephaly, hypertelorism and ectrodactyly syndrome was mapped 2.5 Mb proximal at 118.4 Mb and the candidate genes identified from this region were the insulin-induced protein 2 and the homeobox protein engrailed-1. No clear pathogenic mutations were identified in any of these genes. The breakpoint between INHBB and GLI2 coincides with a previously identified translocation breakpoint associated with ectrodactyly. We propose a mechanism by which translocations in the 2q14.1–q14.2 region disrupt the specific arrangement of long-range regulatory elements that control the tight quantitative spatiotemporal expression of one or more genes from the breakpoint region.

Identification of OAF and PVRL1 as candidate genes for an ocular anomaly characterized by keratolenticular dysgenesis and ectopia lentis

ABSTRACT Keratolenticular dysgenesis (KLD) and ectopia lentis are congenital eye defects. The aim of this study is the identification of molecular genetic alterations responsible for those ocular anomalies with neurologic impairment in an individual with a de novo balanced chromosome translocation t(11;18)(q23.3;q11.2)dn. Disruption of OAF, the human orthologue of the Drosophila oaf, by the 11q23.3 breakpoint results in reduced expression of this transcriptional regulator. Furthermore, four most likely nonfunctional chimeric transcripts comprising up to OAF exon 3, derived from the der(11) allele, have also been identified. This locus has been implicated by publicly available genome‐wide association data in corneal disease and corneal topography. The expression of the poliovirus receptor‐related 1(PVRL1) or nectin cell adhesion molecule 1 (NECTIN1), a paralogue of nectin cell adhesion molecule 3 (PVRL3) associated with congenital ocular defects, situated 500kb upstream from 11q23.3 breakpoint, is increased. The 18q11.2 breakpoint is localized between cutaneous T‐cell lymphoma‐associated antigen 1(CTAGE1) and retinoblastoma binding protein 8 (RBBP8) genes. Genomic imbalance that could contribute to the observed phenotype was excluded. Analysis of gene expression datasets throughout normal murine ocular lens embryogenesis suggests that OAF expression is significantly enriched in the lens from early stages of development through adulthood, whereas PVRL1 is lens‐enriched until E12.5 and then down‐regulated. This contrasts with the observation that the propositas lymphoblastoid cell lines exhibit low OAF and high PVRL1 expression as compared to control, which offers further support that the alterations described above are most likely responsible for the clinical phenotype. Finally, gene interaction topology data for PVRL1 also agree with our proposal that disruption of OAF by the translocation breakpoint and misregulation of PVRL1 due to a position effect contribute to the observed ocular and neurological phenotype. HIGHLIGHTSThe t(11;18)(q23.3;q11.2)dn chromosome translocation associated with type 2 PA and ectopia lentis.Disruption of OAF and misregulation of PVRL1 likely responsible for the ocular phenotype.Expression data during murine lens embryogenesis and from propositas LCLs, collaborate these findings.Genomic interaction data for PVRL1 further supports its involvement.Chimeric OAF transcripts identified from the 11q23.3 breakpoint.

Partial Trisomy of the Pericentromeric Region of Chromosome 5 in a Girl with Binder Phenotype

The patient reported here displayed most characteristic features of Binder syndrome (OMIM: 155050), a rare maxillonasal malformation with unknown etiology. She was sent for genetic evaluation at the age of 10 years because of facial dysmorphism and borderline intellectual disability. Cytogenetic analyses showed a de novo supernumerary small ring chromosome with a pericentromeric region of chromosome 5 in all lymphocytes. Array painting revealed that the marker contains a 20,950-kb genomic region comprising cytogenetic band 5p14.1q11.1. Additionally, 7 reports have been published in the literature with partial trisomy of chromosome 5 overlapping with our case. These 8 cases were analyzed for phenotype/genotype correlation which suggested that the maxillonasal anomalies of Binder phenotype and trisomy of the pericentromeric region of chromosome 5 may be in causal relationship. Future functional annotation studies of genes localized in this genomic region should take this into consideration. To the best of our knowledge, this is the first report on a patient with association of a chromosome abnormality and clinical characteristics of Binder phenotype.

Ring chromosome 6 in a child with anterior segment dysgenesis and review of its overlap with other FOXC1 deletion phenotypes

Here, we report a patient with ring chromosome 6 [r(6)], associated with anterior segment dysgenesis (ASD) and other anomalies. The phenotype was due to a 1880 kb microdeletion at 6p25.3 identified by whole‐genome array analysis, and was mainly attributable to a FOXC1 haploinsufficiency. Currently 37 patients with r(6) have been reported. We found that facial dysmorphism, ASD, heart anomalies, brain anomalies, and hearing loss are constant features only in severe cases of r(6), mainly related to hemizygosity of FOXC1. Thus, overlaps with other FOXC1 related phenotypes, such as the 6p25 deletion syndrome, Axenfeld‐Rieger syndrome type 3, and ASD type 3. Contrarily, those patients whose r(6) does not disrupt FOXC1, have mild or moderate phenotypes and do not exhibit ASD.