Therapeutic strategies for autism: targeting three levels of the central dogma of molecular biology

Translational Psychiatry EXPERT REVIEW www.nature.com/tp OPEN Therapeutic strategies for autism: targeting three levels of the central dogma of molecular biology Derek Hong 1,2 and Lilia M. Iakoucheva 1,3 ✉ 1234567890();,: © The Author(s) 2023 The past decade has yielded much success in the identification of risk genes for Autism Spectrum Disorder (ASD), with many studies implicating loss-of-function (LoF) mutations within these genes. Despite this, no significant clinical advances have been made so far in the development of therapeutics for ASD. Given the role of LoF mutations in ASD etiology, many of the therapeutics in development are designed to rescue the haploinsufficient effect of genes at the transcriptional, translational, and protein levels. This review will discuss the various therapeutic techniques being developed from each level of the central dogma with examples including: CRISPR activation (CRISPRa) and gene replacement at the DNA level, antisense oligonucleotides (ASOs) at the mRNA level, and small-molecule drugs at the protein level, followed by a review of current delivery methods for these therapeutics. Since central nervous system (CNS) penetrance is of utmost importance for ASD therapeutics, it is especially necessary to evaluate delivery methods that have higher efficiency in crossing the blood-brain barrier (BBB). Translational Psychiatry (2023)13:58 ; https://doi.org/10.1038/s41398-023-02356-y INTRODUCTION Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder (NDD) that is characterized by three core symptoms: the deficits in social interaction and communication, language development, and restrictive and repetitive behaviors. A large proportion of children diagnosed with ASD manifest additional symptoms including cognitive deficits, developmental delay, anxiety and other medical comorbidities with mood and psychiatric disorders [1, 2]. As of 2021, the CDC has approximated that 1 in 44, or ~2.3%, of children in the United States have ASD diagnosis [3]. The estimates suggest that 70% of individuals with ASD have limited ability to live independently [4]. This lifelong dependency on caregivers as well as ASD-associated social, cognitive, and behavioral deficits can contribute to parental stress, leading to increased divorce rates in parents of ASD-diagnosed children [5]. At a financial level, the projected cost of the resources needed to care for individuals with ASD will progressively increase to $5.54 trillion/year by 2060 due special education costs, productivity loss due to informal caretaking, and increased use of healthcare services [6]. Given the prevalence of diagnosis, familial stress, and societal financial burden, it is imperative to develop and refine techniques to alleviate the social, cognitive, and behavioral symptoms in ASD. It is well-established that ASD has strong genetic basis. Earlier studies demonstrated that monozygotic twins have significantly greater concordance for ASD than dizygotic twins, and ASD heritability is estimated to be 83% [7]. While individuals with some monogenic causes, such as Angelman Syndrome (AS), Fragile X Syndrome (FXS), and Rett Syndrome (RTT) [8–10], have features of ASD, the etiology of ASD as a whole is extremely heterogeneous [11, 12]. Earlier studies have identified rare de novo and inherited copy number variants (CNV) as major contributors to the increased risk for ASD [13–19]. Subsequently, whole exome sequencing (WES) of simplex families with one affected child demonstrated strong association of rare de novo exonic single nucleotide variants (SNV) with ASD [20–24], with more recent analyses highlighting around a hundred genome-wide significant ASD risk genes [25, 26]. For a subset of genes that are highly past genomewide significant cut-off (at least FDR < 0.05), such as KMT2E, ANKRD11, ARID1B, CHD8, PTEN, SHANK3, DYRK1A, and CUL3, mouse models have been developed over the years [27–34]. Furthermore, non-human primate (NHP) models have been established for the MECP2 (implicated in RTT) and SHANK3 genes within cynomolgus macaques (Macaca fascicularis) to better recapitulate human developmental time points [35, 36]. These models have further implicated heterozygous loss-of-function (LoF) mutations (also known as haploinsufficiency) in these genes as responsible for specific neurobiological and behavioral animal phenotypes. In addition to rare de novo variants, a recent genome-wide association study (GWAS) has identified 5 genome-widesignificant ASD loci [37]. Given such an extreme genetic heterogeneity, and an unequivocal role of LoF-impacted (and often haploinsufficient) genes in ASD etiology, it will be invaluable to shift from identification-based research and proceed to investigate therapeutic techniques that could increase the expre ssion of these genes. The therapeutic interventions in ASD aimed at rescuing haploinsufficiency of individual genes could be developed to target all three levels of the central dogma of molecular biology: DNA, mRNA, and protein (Fig. 1). Examples of such interventions include genome editing with CRISPR at the genetic level, antisense 1 Department of Psychiatry, University of California San Diego, La Jolla, CA, USA. 2Division of Biological Sciences, University of California San Diego, La Jolla, CA, USA. 3Institute for Genomic Medicine, University of California San Diego, La Jolla, CA, USA. ✉email: Received: 27 September 2022 Revised: 1 February 2023 Accepted: 3 February 2023 D. Hong and L.M. Iakoucheva 2 DNA mRNA ● CRISPRMediated Modifications ● Transgene Delivery ● Antisense Oligonucleotides (ASOs) ● Targeted RNA Editing Protein Small Molecule Drugs ● Fig. 1 Overview of therapeutics for ASD at different levels of the Central Dogma of Molecular Biology that were discussed in this review. The figure lists therapeutics linearly based on the natural progression of gene expression. In the first column, small molecule drugs and CRISPR-based therapeutics are usually developed to treat diseases at the DNA level. In the second column, antisense oligonucleotides (ASOs) are usually developed to treat diseases at the mRNA level. In the third column, small molecule drugs are usually developed to treat diseases at the protein level. Specific examples of each of these therapeutics are described throughout the review. oligonucleotides (ASOs) at both, the transcriptional and posttranscriptional level, and the use of small-molecule drugs to target molecular pathways at the translational, or protein level. This review will analyze the advantages and disadvantages of the various techniques across the central dogma in order to rescue ASD-associated phenotypes. RESCUE AT THE DNA LEVEL Gene therapy encompasses techniques that can alter the expression of an organism’s genes by targeting the DNA either through transgene delivery, or by direct modification of the genome, with the goal of therapeutically restoring a pathologically expressed gene to normal expression levels [38 (...truncated)