Investigação funcional do novo locus candidato, HDAC9, causativo da síndrome aurículo-condilar

Abstract

Auriculocondylar Syndrome (ACS) is a rare genetic disease that affects structures from the first and second pharyngeal arch, resulting in micrognathia, auricular malformations and dysplasia of the mandibular condyle. The ACS mostly segregates in an autosomal dominant manner with incomplete penetrance, but there are few reported cases whose pattern is autosomal recessive.In addition, there is inter and intra-familial variable expressivity and also genetic heterogeneity.To date, variants have been identified in three genes involved in the EDN1-DLX5/6 pathway: GNAI3, PLCB4 and EDN1. Studies carried out in our laboratory suggested the existence of a fourth locus related to the syndrome, since mutations in the 3 genes already associated with ACS were excluded and linkage studies in a Brazilian family with 11 affected individuals indicated that the variant is located on chromosome 7 (7p21.1-p15.2). In a collaborative work with the University of Oxford, we identified a tandem duplication of circa 400kb in the candidate region of chromosome 7, which includes the HDAC9 gene, in the individuals of this Brazilian family affected by the ACS.The present study aimed, therefore, to investigate the causative variant of ACS in this family in order to verify whether the duplication identified on chromosome 7 has a causal relationship with the phenotype, since it is the only family with changes in this region so far. To answer our research question, we used induced pluripotent stem cells (iPSC) as a model to recapitulate different stages of embryonic development and to investigate which cellular processes and alterations in gene expression could be associated with ACS in these patients. We observed increased expression of the HDAC9 and TWIST1 genes and decreased migration in neural crest cells. We also observed a dysregulation in osteogenic and chondrogenic differentiation in affected cells. These findings support the hypothesis of pathogenicity of the duplication within HDAC9 and its involvement in ACS phenotype in this family.