New locus underlying auriculocondylar syndrome (ARCND): 430 kb duplication involvingTWIST1regulatory elements

Abstract

BackgroundAuriculocondylar syndrome (ARCND) is a rare genetic disease that affects structures derived from the first and second pharyngeal arches, mainly resulting in micrognathia and auricular malformations. To date, pathogenic variants have been identified in three genes involved in the EDN1-DLX5/6 pathway (PLCB4, GNAI3 and EDN1) and some cases remain unsolved. Here we studied a large unsolved four-generation family.MethodsWe performed linkage analysis, resequencing and Capture-C to investigate the causative variant of this family. To test the pathogenicity of the CNV found, we modelled the disease in patient craniofacial progenitor cells, including induced pluripotent cell (iPSC)-derived neural crest and mesenchymal cells.ResultsThis study highlights a fourth locus causative of ARCND, represented by a tandem duplication of 430 kb in a candidate region on chromosome 7 defined by linkage analysis. This duplication segregates with the disease in the family (LOD score=2.88) and includes HDAC9, which is located over 200 kb telomeric to the top candidate gene TWIST1. Notably, Capture-C analysis revealed multiple cis interactions between the TWIST1 promoter and possible regulatory elements within the duplicated region. Modelling of the disease revealed an increased expression of HDAC9 and its neighbouring gene, TWIST1, in neural crest cells. We also identified decreased migration of iPSC-derived neural crest cells together with dysregulation of osteogenic differentiation in iPSC-affected mesenchymal stem cells.ConclusionOur findings support the hypothesis that the 430 kb duplication is causative of the ARCND phenotype in this family and that deregulation of TWIST1 expression during craniofacial development can contribute to the phenotype.

Genomic complexity and complex chromosomal rearrangements in genetic diagnosis: example from two emblematic cases on chromosome 7

“…Therefore, it has been suggested that trisomy 7p cases with delayed closure of fontanels can be a result of TWIST gene dosage effect. In addition, in a recent work, Romanelli Tavares et al 20 studying auriculocondylar polygenic syndrome (ARCND) identi ed a unique 430 Kb tandem duplication at the HDAC9/TWIST1 locus that may cause deregulation of TWIST1 expression, interfering with its regulatory elements. This CNV induced the development of ARCND features through compromised neural crest migration and osteogenic differentiation.…”

Genomic Complexity and Complex Chromosomal Rearrangements in Genetic Diagnosis: Two Illustrative Cases on Chromosome 7

“…Therefore, it has been suggested that trisomy 7p cases with delayed closure of fontanels can be a result of the TWIST gene dosage effect. In addition, in a recent study, Romanelli Tavares et al [ 23 ], studying auriculocondylar polygenic syndrome (ARCND), identified a unique 430 Kb tandem duplication at the HDAC9/TWIST1 locus that may cause deregulation of TWIST1 expression, interfering with its regulatory elements. By impairing osteogenic differentiation and neural crest migration, this copy number variant led to the development of ARCND characteristics.…”