Heterogeneous Genotype-Phenotype Associations in TRIO-Related Neurodevelopmental Disorder Revealed by Meta-Analysis

Background The trio Rho guanine nucleotide exchange factor gene (TRIO) is highly expressed in the developing brain and contributes to neuronal development, specifically axon guidance, synaptogenesis, and cytoskeleton organization. Pathogenic TRIO variants are associated with a neurodevelopmental disorder with substantial phenotypic heterogeneity. Prior case series suggested genotype-phenotype associations related to variant type and location in the protein. However, these results need validation in a larger sample. The objectives of this research were to examine associations between phenotype, variant location and variant type among previously reported TRIO-related neurodevelopmental disorder cases, and identify recurrent TRIO variants.

Eighty-seven previously published studies annotated in the Human Gene Mutation Database reporting at least one TRIO variant were identified. Thirty-two additional cases were ascertained from the Simons Searchlight Study. A total of 699 individual case records were reviewed. After removing redundant cases, 449 unique records remained with available genotype data, of which 228 also had available phenotype information. Along with descriptive statistics, Chi-square analysis was used to test associations between variant and head size.

In a meta-analysis of reported TRIO variants, categorically-defined head size is associated with variant type (missense vs truncating) and protein domain location (χ2 = 39.20; p = <0.001). Specifically, missense variants in the spectrin repeat domain are associated with macrocephaly whereas missense variants outside the spectrin domain and truncating variants are associated with microcephaly. The most prevalent phenotypic features were intellectual disability/developmental delay followed by autism spectrum disorder (ASD) or ASD-like behaviors. Seven recurrent TRIO variants were identified, with head size consistent across cases with the same variant.

TRIO variant type and location exhibit unique phenotypic associations. This observation may help clinicians and families to anticipate neurodevelopmental outcomes. Furthermore, identified recurrent variants may serve as targets for future translational and pharmacological research. Competing Interest Statement The authors have declared no competing interest. Funding Statement We acknowledge NIH grant MH132775 for support to A.G. and a sum-mer research support grant to S.D. from the Feinberg School of Medicine. Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Northwestern University Institutional Review Board classified access to deidentified data in Simons Searchlight as not human subjects research. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Data Availability Data from the Simons Searchlight study are available by direct request to the Simons Foundation (https://base.sfari.org). All other data generated from meta-analysis are included in this article and its supplementary information files.