Presynaptic dysfunction in CASK-related neurodevelopmental disorders

Martin Becker,Sven Bölte,Josephine Wincent,Britt‐Marie Anderlid ,Anna Falk,Charlotte Willfors,Eric Herlenius,Danyang Li,Ielyzaveta Rabkina,Simon Maier,Rouslan Sitnikov,Malin Kele,Viveka Moritz,Mai‐Lan Ho ,Janina Neufeld,Francesca Mastropasqua,Lynnea Myers,Lea Ballenberger,Jan Philipp Reising,Kristiina Tammimies

doi:10.1038/s41398-020-00994-0

Abstract

CASK-related disorders are genetically defined neurodevelopmental syndromes. There is limited information about the effects of CASK mutations in human neurons. Therefore, we sought to delineate CASK-mutation consequences and neuronal effects using induced pluripotent stem cell-derived neurons from two mutation carriers. One male case with autism spectrum disorder carried a novel splice-site mutation and a female case with intellectual disability carried an intragenic tandem duplication. We show reduction of CASK protein in maturing neurons from the mutation carriers, which leads to significant downregulation of genes involved in presynaptic development and of CASK protein interactors. Furthermore, CASK-deficient neurons showed decreased inhibitory presynapse size as indicated by VGAT staining, which may alter the excitatory–inhibitory (E/I) balance in developing neural circuitries. Using in vivo magnetic resonance spectroscopy quantification of GABA in the male mutation carrier, we further highlight the possibility to validate in vitro cellular data in the brain. Our data show that future pharmacological and clinical studies on targeting presynapses and E/I imbalance could lead to specific treatments for CASK-related disorders.

Highlights

The identification of genetic variants underlying neurodevelopmental disorders (NDDs), such as intellectual disability (ID), autism spectrum disorder (ASD), and attention-deficit hyperactivity disorder (ADHD), as well as epilepsies, has increased at a rapid pace in recent years with a high level of pleiotropy across the conditions[1,2,3]
We identified a male individual diagnosed with ASD carrying a calmodulin-dependent serine protein kinase (CASK) mutation from the Roots of Autism and ADHD Twin Study in Sweden (RATSS)[24]
Rare variants from the exome sequencing were prioritized based on variant effect, inheritance mode, and genes involved in NDDs

Summary

Introduction

The identification of genetic variants underlying neurodevelopmental disorders (NDDs), such as intellectual disability (ID), autism spectrum disorder (ASD), and attention-deficit hyperactivity disorder (ADHD), as well as epilepsies, has increased at a rapid pace in recent years with a high level of pleiotropy across the conditions[1,2,3]. Findings indicate shared molecular mechanisms underlying the diverse clinical phenotypes. For many of the identified risk variants and genes, the molecular and neuronal outcomes are not well understood. One pleiotropic gene is the calcium/calmodulin-dependent serine protein kinase (CASK), located on chromosome Xp11.4, in linked ID (XL-ID), developmental delay (DD), and ASD1,4–6. The majority of cases reported with CASK-. Related disorders are females with MICPCH, caused by heterozygous loss-of-function (LoF) variants[5,7].

Methods

Results

Conclusion