SummaryOtosclerosis is a condition characterized by an abnormal bone metabolism in the otic capsule, resulting in conductive and/or sensorineural hearing loss. Otosclerosis is a common disorder in which genes play an important role. Case-control association studies have implicated several genes in the abnormal bone metabolism associated with otosclerosis: COL1A1, TGFB1, BMP2, and BMP4. To investigate the association of these genes with otosclerosis in the Tunisian population, we examined nine single nucleotide polymorphisms (SNPs) in 159 unrelated otosclerosis patients and 155 unrelated controls. We found an association of rs11327935 in COL1A1 with otosclerosis that was shown to be sex specific. The coding polymorphism T263I in TGFB1 was also associated with otosclerosis in the Tunisian population. The effect sizes of both the associations were consistent with previous studies, as the same effect was found in all cases. The association of BMP2 and BMP4 was not significant. However, a trend towards association was found for the BMP4 gene that was consistent with earlier reports. In conclusion, this study replicates and strengthens the evidence for association between polymorphisms of COL1A1 and TGFB1 in the genetic aetiology of otosclerosis.

SummaryOtosclerosis is a common form of conductive hearing loss, caused by an abnormal bone remodelling in the otic capsule. Both environmental and genetic factors have been implicated in the etiology of this disease. A recent genome wide association study identified two regions associated with otosclerosis, one on chr7q22.1, located in the RELN gene, and one on chr11q13.1. A second study in four European populations has replicated the association of the RELN gene with otosclerosis. To investigate the association of these loci with otosclerosis in a non-European population, we tested 11 SNPs from the two regions in 149 unrelated Tunisian patients and 152 controls. Four SNPs were significantly associated with otosclerosis. Three SNPs are located in the RELN region and the last one is located in the region on chromosome 11. We also observed a significant interaction with gender for rs3914132. This suggests an influence of sex on the association of RELN with otosclerosis. A meta-analysis showed that the disease-associated alleles in the Tunisian sample are the same as in all previously reported associations. Our study provides additional evidence implicating RELN in the development of otosclerosis. Additional functional studies should determine the role of RELN in the physiopathology of this disease.

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Otosclerosis is a disease of abnormal bone remodeling in the human otic capsule that can lead to progressive hearing loss. Little of the underlying disease etiology has been elucidated thus far, although several studies have suggested that COL1A1 may play a role based on its importance in bone metabolism and other diseases like osteoporosis and osteogenesis imperfecta. Genetic association studies between COL1A1 and otosclerosis, however, have been contradictory. To resolve this issue, we studied a large Belgian-Dutch and a Swiss population for a genetic association between COL1A1 and otosclerosis and additionally performed a meta-analysis to investigate the overall genetic effect of COL1A1 on all otosclerosis populations studied to date. We found a significant association both in the Belgian-Dutch population and in the meta-analysis. In aggregate, our analysis supports evidence for an association between COL1A1 and otosclerosis although effect sizes of the variants reported in the initial studies are likely to be an overestimate of true effect sizes.

Induced pluripotent stem cells (iPSCs) have brought great promises for disease modeling and cell-based therapies. One concern related to the use of reprogrammed somatic cells is the loss of genomic integrity and chromosome stability, a hallmark for cancer and many other human disorders. We investigated 16 human iPSC lines reprogrammed by nonintegrative Sendai virus (SeV) and another 16 iPSC lines generated by integrative lentivirus for genetic changes. At early passages we detected cytogenetic rearrangements in 44% (7/16) of iPSC lines generated by lentiviral integration whereas the corresponding figure was 6% (1/16) using SeV-based delivery. The rearrangements were numerical and/or structural with chromosomes 5 and 12 as the most frequently involved chromosomes. Three iPSC lines with chromosome 5 aberrations were derived from one and the same donor. We present in this study the aberrant karyotypes including a duplication of chromosome 5q13q33 that restricts a candidate region for growth advantage. Our results suggest that the use of integrative lentivirus confers a higher risk for cytogenetic abnormalities at early passages when compared to SeV-based reprogramming. In combination, our findings expand the knowledge on acquired cytogenetic aberrations in iPSC after reprogramming and during culture.

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Mowat-Wilson syndrome (MWS) is a severe neurodevelopmental disorder caused by heterozygous variants in the gene encoding transcription factor ZEB2. Affected individuals present with structural brain abnormalities, speech delay and epilepsy. In mice, conditional loss of Zeb2 causes hippocampal degeneration, altered migration and differentiation of GABAergic interneurons, a heterogeneous population of mainly inhibitory neurons of importance for maintaining normal excitability. To get insights into GABAergic development and function in MWS we investigated ZEB2 haploinsufficient induced pluripotent stem cells (iPSC) of MWS subjects together with iPSC of healthy donors. Analysis of RNA-sequencing data at two time points of GABAergic development revealed an attenuated interneuronal identity in MWS subject derived iPSC with enrichment of differentially expressed genes required for transcriptional regulation, cell fate transition and forebrain patterning. The ZEB2 haploinsufficient neural stem cells (NSCs) showed downregulation of genes required for ventral telencephalon specification, such as FOXG1, accompanied by an impaired migratory capacity. Further differentiation into GABAergic interneuronal cells uncovered upregulation of transcription factors promoting pallial and excitatory neurons whereas cortical markers were downregulated. The differentially expressed genes formed a neural protein-protein network with extensive connections to well-established epilepsy genes. Analysis of electrophysiological properties in ZEB2 haploinsufficient GABAergic cells revealed overt perturbations manifested as impaired firing of repeated action potentials. Our iPSC model of ZEB2 haploinsufficient GABAergic development thus uncovers a dysregulated gene network leading to immature interneurons with mixed identity and altered electrophysiological properties, suggesting mechanisms contributing to the neuropathogenesis and seizures in MWS.