Molecular Etiology of a Novel SMC1A-linked Neurodevelopmental and Epileptic Disorder
Abstract number :
1.446
Submission category :
1. Basic Mechanisms / 1E. Models
Year :
2022
Submission ID :
2232852
Source :
www.aesnet.org
Presentation date :
12/3/2022 12:00:00 PM
Published date :
Nov 22, 2022, 05:27 AM
Authors :
Xiuhua Bozarth, MD, PhD – Seattle Children's Hospital, University of Washington; Xinxian Deng, PhD – University of Washington; Christine Disteche, PhD – University of Washington; Zhijun Duan, PhD – University of Washington; He Fang, Postdoc fellow – University of Washington; Gala Filippova, Research scientist – University of Washington; Camille Groneckv, Scientist – University of Washington
This is a Late Breaking abstract
Rationale: X-linked SMC1A encodes a core subunit of the cohesin complex which plays pivotal roles in genome organization and gene regulation. Mutations in SMC1A are often dominant-negative and typically cause Cornelia de Lange syndrome with growth retardation and typical facial features. However, SMC1A loss-of-function (LOF) mutations cause a novel clinical phenotype of developmental and epileptic encephalopathy (DEE) with intractable early-onset epilepsy severe intellectual disability, and hand wringing. These SMC1A-DEE mutations are found exclusively in heterozygous girls due to presumed lethality in males. This situation is reminiscent of Rett syndrome (RTT) caused by X-linked MECP2 mutations in girls. Interestingly, mutations of other chromatin regulators are also implicated in RTT-like phenotypes, suggesting a common chromatin role in brain development and function. We hypothesize that heterozygous SMC1A-DEE mutations reduce cohesin and disrupt genome organization in a mosaic fashion due to differential dosage effects in cells depending on the mutant location on the Xa or the Xi.
Methods: We characterized SMC1A-DEE mutations and derived induced pluripotent stem cell (iPSC) lines by reprogramming peripheral blood mononuclear cells from patients and normal parent controls. We then differentiated these iPSC lines into two- and three-dimensional neural models to examine how SMC1A mutations affect the neuronal differentiation. We determine molecular effects of these mutations on 3D chromosomal structure by Hi-C and gene expression by RNA-seq.
Results: We confirmed our three heterozygous SMC1A-DEE mutations and surveyed their X inactivation patterns, which is possibly linked to the severity of phenotype. We also confirmed the predicted effect of the de novo SMC1A splice-site mutation of P1 (c.615+G >A) on transcriptional splicing, leading to loss of function. Interestingly, our study in neural precursor cells from P1 has uncovered alterations in chromatin loops and heterochromatin conformation as well as in neuronal gene expression. These disruptions are more pronounced in cells with the SMC1A splice-site mutation on the active (Xa) vs. inactive X (Xi), suggesting a differential dosage effect since SMC1A escapes X-chromosome inactivation and its expression from the Xi is lower than that from the Xa. Examination of differential (high or low mutant dose) and mosaic dosage effects of SMC1A-DEE mutations in 3D cortical organoids is ongoing. Our study will provide new insights into the mechanisms of these chromatin disorders and potential avenues for prevention, diagnosis, and therapy of pediatric epilepsies.
Conclusions: SMC1A-DEE mutations have a special dosage-dependent effect on chromatin loops and heterochromatin conformation, neuronal gene expression, and cortical organoid development, suggesting a dosage sensitive role of SMC1A in early brain function and development and a potential etiology linked to DDE.
Funding: AES seed grant
Basic Mechanisms