EPOS

European Paediatric Ophthalmological Society

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FOXC1/PITX2 mutations and copy number changes in a Belgian-Dutch cohort of patients with anterior segment dysgenesis (ASD)

D'haene Barbara¹, de Ravel Thomy², Leroy Bart³, Plomp Astrid⁴, Meire Francoise⁵, De Baere Elfride^1
1Center for Medical Genetics, Ghent University Hospital, Belgium, ²Center for Human Genetics, Catholic Leuven University, Belgium, ³Department of Ophthalmology, Ghent University Hospital, Belgium, ⁴Department of Medical Genetics, AMC, Amsterdam, The Netherlands, ⁵HUDERF, Brussels, Belgium

Anterior segment dysgenesis (ASD) refers to a group of rare developmental disorders of the anterior eye segment, which display mostly an autosomal dominant inheritance pattern. Disease-causing mutations or copy number changes of FOXC1 and PITX2 account for 40% of the molecular defects in ASD patients. A primary purpose of this study was to determine the prevalence of disease-causing FOXC1/PITX2 mutations and copy number changes in a Belgian-Dutch cohort of ASD patients. Sixty-four probands, mainly of Belgian-Dutch origin, were examined for copy number changes of FOXC1/PITX2 with MLPA and screened for subtle FOXC1/PITX2 mutations by sequencing. MLPA revealed 5 FOXC1 deletions and 4 PITX2 deletions. Furthermore sequencing revealed 1 known and 7 novel FOXC1 mutations and 1 known and 6 novel PITX2 mutations. In this cohort the underlying genetic cause was revealed in 38% of the patients, which sustains the major role of the FOXC1/PITX2 genes in the molecular pathogenesis of ASD in the Belgian-Dutch population. The molecular data are currently being complemented by phenotypic information in an attempt to establish genotype-phenotype correlations. A second aim was to delineate FOXC1 and PITX2 deletions in order to unravel their underlying mechanism. ArrayCGH with a tiling BAC array for the FOXC1 region was carried out for 4 patients with a known FOXC1 deletion. In addition, 3 PITX2 deletions were further delineated with SNP chip copy number screening. Subsequently, 1 PITX2 deletion of maximum 2.5 Mb in size was further defined using quantitative PCR (qPCR), which enabled us to pinpoint the deletion breakpoints to a region of 4639 bp at the centromeric end, and of 786 bp at the telomeric end of the deletion. The precise location of the breakpoints is currently being characterized by long-range PCR and sequencing. Overall, these results show a scattered location of the breakpoints, which is in line with previous findings. These non-recurrent rearrangement events propose non-homologous end joining (NHEJ) or Fork Stalling and Template Switching (FoSTeS) as possible underlying mechanisms.