Abstract 1426 CTBP1 Mutation Affects Neurodevelopment

Hypotonia, Ataxia, and Delayed Development Syndrome (HADDS) is a rare neurodevelopmental disease leading to congenital hypotonia, delayed psychomotor development, intellectual disability and is often associated with cerebellar atrophy in patients. A de novo missense mutation in the CTBP1 missense (c.991C > T, p.R342W) allele has been linked with HADDS. The C-terminal binding proteins (CtBP1 and CtBP2) are highly conserved and expressed in vertebrates. CtBPs are co-repressors that bind to various chromatin-modifying factors and DNA binding repressors at the promoter regions of target genes through a protein interaction interface (PXDLS-binding cleft). It has been shown that the CTBP1 mutation is found at the C-terminus of the PXDLS binding cleft and a change in its charge can alter important protein interactions that cause chromatin modification and affect gene expression. Patients with HADDS harbor a single de novo heterozygous missense mutation (c.991C > T, p.R342W) within the PXDLS-binding cleft of CtBP1. In previous work from our laboratory, fibroblasts isolated from biopsy samples of a patient were reprogrammed into induced pluripotent stem cells (iPSCs) and then differentiated into neuronal cell models. These models were used to determine transcriptional activities of the pathogenic CTBP1 p.R342W allele. In addition, these models were used to understand functional abnormalities in neurons. To eliminate genetic variability associated with patient-derived iPSCs, we derived isogenic cell lines harboring heterozygous and homozygous mutations for the pathogenic CTBP1 p.R342W allele. Transcriptome analysis of the differentiated neurons from these isogenic cell lines indicated that several genes involved in adhesion, neurodevelopment, and several pathways, such as the Wnt and Sonic Hedgehog signaling pathways, are downregulated. We therefore hypothesized that the mutated pathogenic CTBP1 allele causes neurodevelopmental defects affecting neurite growth and cell adhesion. We observed morphological differences in neurite growth in differentiated neurons. The mutant neural stem cells (NSCs) exhibited low adhesion compared to parental NSCs. Cell migration in the homozygous and heterozygous cells was significantly lower compared to that of the parental isogenic wild-type cell line. These results show that CTBP1 mutation affects neurodevelopment. Financial support was received from a grant awarded by the DeNardo Education and Research Foundation and an ASBMB Undergraduate Research Award to SL.