What is Autism Spectrum Disorder (ASD) and what are the gene-edited mouse models for autism?

Autism Spectrum Disorder (ASD) refers to a broad range of complex neurodevelopmental conditions that has many theorized causative factors, but there have been many genetic mutations associated with susceptibility to autism and altered brain structure associated with ASD.

Due to the lack of appropriate interpersonal communication and interaction skills, and restricted or repetitive interests or behaviors, it is difficult for autistic patients to understand other people's emotions and express their own feelings. The number of new patients with autism is gradually increasing every year, but unfortunately, the current treatment methods for autism are very limited, and the fact that there is a huge number of patients makes ASD an important subject for scientific research of children's developmental disorders.  Treatment for people with ASD varies depending on their unique strengths and challenges, with the overall goal to improve quality of life by reducing symptoms which interfere with daily functioning.

Now we will introduce the gene-edited mouse models of autism.

01 ASD Introduction

ASD, also known as Autism Spectrum Condition (ASC), is a generalized developmental disorder caused by differences in brain development, symptoms of which include abnormal language and communication skills, narrow interests, and repetitive behavior patterns.^[1] Additionally, people with ASD may have different ways of learning, moving, or paying attention. In 2013, the fifth edition of the Diagnostic Statistical Manual of Mental Disorders (DSMV) in the United States revised the diagnostic criteria for autism and related disorders, canceling the original designation of 'Autism' and updating its classification into Autism Spectrum Disorder (ASD). ASD is an umbrella term which includes autism disorder (classically-known as autism), Asperger's syndrome (AS), pervasive developmental disorder, not otherwise specified (PDD-NOS), and childhood disintegrative disorder (CDD).^[2] Usually, what people refer to as autism more accurately refers to ASD, which is autism in a broad sense.

02 Pathogenesis of ASD

The specific pathogenic mechanism of ASD is unknown. The mainstream view is that it is mainly related to genetics and environment. Data shows that ASD is a highly heritable disease, and the monozygotic twin concordance rate is as high as 90%. A meta-analysis published in 2016 reported that 74-93% of autism risk is heritable, and studies of siblings in the same family showed that after an older child was diagnosed with ASD, subsequent children had a 7 -20% chance of developing ASD.^[3] More than 1,000 genes have been found to be associated with ASD genetic risk, most of which are closely related to normal neural development and connectivity between different functional regions of the brain, suggesting a common pathway leading to ASD risk. ^[4] Genetic abnormalities associated with ASD can be divided into three categories:

1. Single gene mutations: such as mutations found in SHANK3, FMR1, or MECP2;

2. Copy number variations (CNVs): including chromosomal duplications, large deletions, inversions, and translocations;

3. Polygenic risk factors: caused by the accumulation of multiple variants. However, the primary causative gene(s) and specific type of mutation is still under further research.

03 ASD symptoms

The current global incidence of ASD is about 0.6%-1%. In the United States, 1 in 68 children is affected by ASD, and the incidence frequency of boys is 4.5 times that of girls. ASD typically begins before age 3 and lasts a lifetime. As children with ASD grow into adolescents and adults, they have extreme difficulty developing and maintaining friendships or communicating with others, along with symptoms such as anxiety, depression, and attention deficit hyperactivity disorder (ADHD).^[5] At present, the treatment of ASD is mainly symptomatic treatment, mainly aimed at symptoms that interfere with daily function and quality of life. Since ASD affects everyone differently, each patient has different treatment needs and the therapeutic strategies usually involve multiple professional fields. Since the pathogenic mechanism is still unclear, there is currently no etiological treatment or preventative for ASD, and more research on the pathology of ASD is urgently needed.

04 ASD disease models

Data from patients with ASD showed that the following genes all have mutations associated with the risk of ASD: neuroligin (NLGN3/4), neuronal cell surface proteins (NRXN1 and CNTNAP2), SH3 and multiple ankyrin repeat domains protein 3 (SHANK3), methyl-CpG-binding protein 2 (MECP2), fragile X messenger ribonucleoprotein 1 (FMR1), tuberous sclerosis complex (TSC1/2), CHD8, SCN2A, SYNGAP1, TBX1, ARID1B, GRIN2B, and TBR1;^[5]  but not every gene mutation will lead to development of ASD, the pathogenicity of each gene mutation needs sufficient experimental data to verify. In the past decades of research, researchers have constructed a number of autism or autism-like mice induced by deletion of ASD-related genes, which provides more animal models for ASD disease mechanism research, drug target discovery, and developing new treatment methods. The following are several major gene-edited autism mouse models, all of which are notably on C57BL/6J (a.k.a. B6, B6J) mouse strain background (which differs from the B/6N substrain).

Tbx1 Mice (E1-E2 knockout)

Large deletions of the human chromosome 22q11.2 locus can lead to ASD-like phenotypes, but the deletion region contains at least 30 genes, and the specific genes that lead to ASD phenotypes have yet to be identified. The study by Takeshi Hiramoto et al. in 2011 showed that among the more than 30 genes contained in the 22q11.2 large fragment deletion sequence, Tbx1 showed a high degree of correlation with developing ASD, and the heterozygous mice (HT) with Tbx1 single gene deletion showed an ASD-like phenotype with deficits in social interaction, and changes in memory-based behaviors, working memory, and developmental differences. ^[6]

Figure 1. Tbx1 heterozygous mice (HT) exhibited ASD-related behavioral phenotypes

left: frequencies and durations of vocalizations

right: T-maze spontaneous alternation behavior (SAB)^[6] 

Shank3B Mice (E13-E16 knockout)

Mutations in SHANK family genes are associated with syndromic and idiopathic forms of ASD, as well as other neuropsychiatric (e.g. schizophrenia) and neurodevelopmental disorders (e.g. intellectual disability). SHANK3 is a postsynaptic protein whose disruption at the genetic level is responsible for the development of 22q13 deletion syndrome and other non-syndromic ASDs. In a research paper published in Nature, João Peça describes that Shank3 gene-null mice exhibit defects in striatal synapses and cortico-striatal circuits, accompanied by self-injurious repetitive grooming and deficits in social interaction. This study revealed the key role of SHANK3 in the normal development of neuronal connections, and successfully uncovered the link between SHANK3 loss and autism-like behavior in mice.^[7]

                       Figure 2. Shank3B^-/- mice have reduced social interaction and abnormal social novelty recognition^[7]

Cntnap2 Mice (E1 knockout)

CNTNAP2 encodes a neuronal transmembrane protein member of the Neurexin superfamily, which is involved in neuron-glial cell interaction and the accumulation of calcium channels in myelinated axons. Mutations in CNTNAP2 were originally shown to be associated with cortical dysplasia-focal epilepsy syndrome (CDFE), a rare disorder that causes seizures, language regression, intellectual disability, and hyperactivity. Simultaneously, nearly two-thirds of ASD-like phenotypes also exist in patients with CNTNAP2 mutations, and an increasing number of subsequent studies have demonstrated the link between this gene and the increased risk of autism or autism-related endophenotypes. Daniel H. Geschwind et al. have demonstrated that the knockout of the mouse Cntnap2 gene is closely related to ASD and related neurodevelopmental disorders in a research paper published in the journal Cell. Cntnap2^-/- mice exhibit deficits in all three diagnostic symptoms of ASD, accompanied by hyperactivity and seizure phenotypes that are highly consistent with symptoms in patients with CNTNAP2 pathogenic variants,^[8] making this one of the models that most fully represent the human ASD disease phenotype.

 Figure 3. Cntnap2^-/- mice exhibit an ASD phenotype with abnormal communication and social behavior^[8] 

05 Cyagen's Autism Research Mouse Model

Cyagen has thousands of self-developed gene-edited mouse strains, and can provide a series of mouse models related to autism research. The model information is detailed in the table below. At the same time, we can also provide professional customized services according to your project needs to accelerate your research.

                                                                                   Mouse Models of ASD

The Cyagen Knockout Catalog Models repository can fully meet the project needs of basic research and new drug development, which provides off-the-shelf mouse models covering more than 20 research fields such as oncology, cardiovascular, and neurology. The powerful database offers you a more convenient experience for obtaining knockout mice on a 100% pure B6 background, with delivery in as fast as 2 weeks . Researchers can search  our repository of over 16,000 KO/cKO mice to discover research models, compare data, and request a quote.

Reference:

[1]Lord C, Elsabbagh M, Baird G, et al. Autism spectrum disorder[J]. Lancet, 2018, 392(10146): 508-20.

[2]Wakefield, J.C. DSM-5: An Overview of Changes and Controversies. Clin Soc Work J 41, 139–154 (2013).

[3]Tick B, Bolton P, F Happé, et al. Heritability of autism spectrum disorders: a meta‐analysis of twin studies[J]. Journal of Child Psychology & Psychiatry, 2016, 57.

[4]Geschwind, Daniel, H, et al. Gene hunting in autism spectrum disorder: on the path to precision medicine[J]. Lancet Neurology, 2015.

[5]Varghese M,Keshav N,Jacot-Descombes S,et al. Autism spectrum disorder:Neuropathology and animal models[J]. Acta Neuropathol,2017,134(4):537-566.

[6]Takeshi, Hiramoto, Gina, et al. Tbx1: identification of a 22q11.2 gene as a risk factor for autism spectrum disorder in a mouse model.[J]. Human Molecular Genetics, 2011.

[7]Peça J, Feliciano C, Ting J T, et al. Shank3 mutant mice display autistic-like behaviours and striatal dysfunction[J]. Nature, 2011, 472(7344):437.

[8]Pe Agarikano O, Abrahams B, Herman E, et al. Absence of CNTNAP2 leads to epilepsy, neuronal migration abnormalities, and core autism-related deficits.[J]. Cell, 2011, 147(1):235-246.

[9]Wang Jianfei, Han Junhai, Zhang Zichao. Behavioral analyses in mouse models of autism spectrum disorders[J].Hereditas(Beijing),2021,43(5): 501-519.