Early Translational II
Autism is a highly heritable and often severe neurodevelopmental disorder, with no biomarkers of disease and no pharmacological intervention for core symptoms. The genetic basis in most patients is unknown and likely complex, however several simpler syndromes with known genetic mutations are strongly associated with autism, including those affecting the ras-MAPK signalling pathway. Drug discovery must be based on an understanding of the genetic, molecular, cellular or systemic basis of dysfunction. Without biomarkers of autism, we cannot develop etiologically relevant treatments. However, brain imaging has not yielded definitive results, brain tissue samples are difficult to obtain, and rodents cannot model the human-specific aspects. By generating induced pluripotent stem cells (iPSCs) and using these to create a neuronal model, we can analyze neuronal properties, such as growth and viability, signaling, and formation of synapses. We will develop an iPSC model from subjects with known mutations causing a ras-MAPK pathway syndrome, in order to identify biomarkers and enable drug screening for both rare syndromes and idiopathic autism.
Statement of Benefit to California:
Autism affects nearly 1% of children, and is a high priority concern in California. Affected individuals and families currently require a substantial amount of behavioral treatment and support for a lifelong and often incapacitating disability. Current research in model organisms suggest that other presumed neurodevelopmental disabilities can be reversed pharmacologically in adulthood, such as those associated with neurofibromatosis type I (NF1), which is strongly associated with autism. This proposal aims to identify biomarkers for autism by using rare disorders with known genetic mutations, such as NF1 and other disorders of the ras-MAPK signalling pathway. With the identification of biomarkers, identification of pharmacological treatments will be feasible.
This application for a Development Candidate Feasibility Award seeks to develop a cellular model of autism for small molecule screening. The applicant proposes to derive induced pluripotent stem cells (iPSCs) from patients with genetic mutations in the Ras-MAPK signaling pathway. These mutations cause diseases collectively known as RASopathies, which share some cognitive symptoms with autism. The applicant proposes three Specific Aims: (1) to reprogram fibroblasts from RASopathy patients into iPSCs and differentiate those cells into neurons; (2) to develop assays to quantitatively analyze these neurons; and (3) to use these neurons to screen small molecules for disease-modifying activity. Reviewers agreed that the goal of generating a cellular model of autism is critical, as there are no effective treatment options and patient neurons are inaccessible for drug screening. However, reviewers questioned the scientific rationale for choosing RASopathies as the basis of the model. Numerous studies have indicated that autism is a multi-factorial disease, but the RASopathies have known mutations in defined genes that may not be linked to idiopathic autism. The reviewers were concerned that any neuronal phenotypes generated would be related to Ras-MAPK signaling defects and not relevant to the vast majority of autism patients. The reviewers found the preliminary data to be insufficient to support the feasibility of the proposal. There were no data supporting the generation, characterization or differentiation of iPSCs from RASopathy patients. Data in support of Aim 2 were also lacking, as were precise details of the assays proposed to evaluate neuronal phenotypes. Reviewers cautioned that scaling up these assays for drug screening would be quite difficult, and they were concerned that this process was not outlined in the application. Further, they noted that it would require several weeks for iPSCs to differentiate and mature into neurons, a process that may be quite difficult to achieve in 384-well screening plates as proposed. Reviewers described the Principal Investigator (PI) as an expert in human genetics, but they were not convinced that she/he has the appropriate experience to carry out the proposed project. They noted that the PI reported collaborations with investigators with expertise in iPSC derivation, neural differentiation and electrophysiology, but supporting letters were not provided. In summary, this is a proposal to develop a cellular model of autism to be employed in drug screening. A key strength of the proposal is its focus on an unmet medical need. Serious weaknesses include the project’s scientific rationale, a number of significant problems with the experimental plan, and lack of sufficient preliminary data and appropriate expertise. These deficiencies significantly diminished reviewer enthusiasm for the project.