Gaining insights: the effects of the RMK gain-of-function mutations on brain development and neurodevelopmental disorders

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Project Summary/Abstract Rare genetic disorders are a major cause of human morbidity, frequently affect brain development and cause neurodevelopmental disorders. Here, we propose using Noonan syndrome (NS, 1:2000) as a human model system to provide critical data on the effects of Ras/mitogen-activated protein kinase (RMK)-genetic alterations on the human brain's complex systems-level biology. Three lines of evidence support using NS as a human model system: 1) NS is caused by autosomal dominant mutations of high penetrance in specific genes compared to idiopathic neurodevelopmental disorders genetics of common variance, 2) NS has a larger impact on brain development and thus larger effect sizes than idiopathic neurodevelopmental disorders, 3) NS is associated with increased risk for neurodevelopmental disorders such as attention abilities, learning disabilities, and autism spectrum symptoms. Our lab has recently observed the effect of NS mutations in the PTPN11 gene on human brain structure, specifically the striatum, and brain function, specifically frontostriatal connectivity. However, there is limited data available on the effect of other NS mutations, RAF1 and SOS1, on the developing brain. To address this limitation, we propose determining whether three major NS disease genes RAF1, PTPN11, and SOS1 mutations, are associated with striatal alteration in a gradient of severity. To provide critical data on the relationships between PTPN11 genetic variance and brain development, we will test whether PTPN11 pathogenic variants are associated with altered brain development. Finally, we will test whether whole-brain connectivity can predict attention abilities in NS. This aim will provide a neuromarker for attention abilities (specifically inhibition) in NS. We will perform "deep phenotyping" - imaging studies of the striatum (volume, cellular density, seed-based functional connectivity) and the whole brain (surface area, cortical thickness, white matter, cortical myelin content, and whole-brain functional connectivity) and assess attention (inhibition) in children (7-16 years of age) with RAF1 (n=30), PTPN11 (n=45), and SOS1 (n=30) mutations, and compare them to typically developing controls (n=45). Two innovative aspects of the proposed work are using restriction spectrum imaging (RSI) to map the RMK pathway upregulation effect on the striatum cellular density. Second, we will assess the effect of RAF1 mutations on brain development for the first time. Defining the relationships between the brain and Noonan's genetics will accelerate the use of genetic testing to inform prognosis and treatments in NS. Further, describing these relationships will provide critical data on the role of the RMK in brain development.