Understanding how genetic variants in the oxytocin receptor gene (OXTR) confer the risk of autism spectrum disorder - a genetic and molecular biology analysis

2018 Fiscal Year Research-status Report

• Project/Area Number: 18K15502
• Research Institution: Institute of Physical and Chemical Research
• Principal Investigator: LIU XIAOXI 国立研究開発法人理化学研究所, 生命医科学研究センター, 基礎科学特別研究員 (20709216)
• Project Period (FY): 2018-04-01 – 2020-03-31
• Keywords: Autism spectrum disorder / Oxytocin receptor (OXTR) / Genetics / Functional study / rare variants

Outline of Annual Research Achievements

Recent studies demonstrate that oxytocin plays a critical role in regulating a wide range of social behaviors including pair bonding, maternal parenting and formation of social memory. Despite tremendous progress in linking genetic variants in OXTR to a wide range of phenotypes and promising results from clinical trial studies, it remains unknown through which genetic and molecular mechanisms these common SNPs exert their influences; and how molecular level changes subsequently modulate complex social behaviors. In this fiscal year. We generated expression vector of one missense mutation identified in Japanese ASD patient which is predicted to be deleterious, we subsequently performed in vitro calcium imaging analysis to measure the oxytocin receptor activation activity and we demonstrated for the first time there is gain-of-function variant in OXTR which significantly enhance the oxytocin response. We further analyzed the whole-genome sequencing data of 5,579 autism spectrum disorder (ASD) individuals and perform genetic analysis to understand the genetic landscape of both common and rare variants in ASD. We identified additional missense mutations from ASD patients which are extremely rare in the general population and we speculate such variants might have functional impacts on the oxytocin single transduction. I

Current Status of Research Progress

2: Research has progressed on the whole more than it was originally planned.

Reason

We conducted in vitro calcium imaging assay to measure one missense mutation and observed the mutation caused over-activation of the OXTR, this would be the first gain-of-function variant and we speculate this implicate an imbalance of excitatory inhibitory balance in autism. We analyzed whole-genome sequencing (WGS) data of 5,579 autism spectrum disorder family samples and we firstly focus on the coding regions of OXTR. By comparing the allele frequency with that obtained from the gnomAD dataset which includes 126,216 exomes and 15,136 whole-genome sequences, we identified 24 rare missense mutations in ASD patietns. We subsequently performed mutagenesis and made the OXTR expression vector bearing such mutations.

Strategy for Future Research Activity

We are now planning to perform functional assay on promising rare missense variants to evaluation the functional impact of these variants by calcium imaging analysis. We will also focus on experiments on non-coding variants identified in ASD patients and evaluate whether they are acting as enhancer elements.

Causes of Carryover

Because the reagent cost is lower than expected. We will use the remaining amount for additional oxytocin ligand biding assay experiments in this year's plan.