TRIO loss of function is associated with mild intellectual disability and affects dendritic branching and synapse function

Hum Mol Genet. 2016 Mar 1;25(5):892-902. doi: 10.1093/hmg/ddv618. Epub 2015 Dec 31.


Recently, we marked TRIO for the first time as a candidate gene for intellectual disability (ID). Across diverse vertebrate species, TRIO is a well-conserved Rho GTPase regulator that is highly expressed in the developing brain. However, little is known about the specific events regulated by TRIO during brain development and its clinical impact in humans when mutated. Routine clinical diagnostic testing identified an intragenic de novo deletion of TRIO in a boy with ID. Targeted sequencing of this gene in over 2300 individuals with ID, identified three additional truncating mutations. All index cases had mild to borderline ID combined with behavioral problems consisting of autistic, hyperactive and/or aggressive behavior. Studies in dissociated rat hippocampal neurons demonstrated the enhancement of dendritic formation by suppressing endogenous TRIO, and similarly decreasing endogenous TRIO in organotypic hippocampal brain slices significantly increased synaptic strength by increasing functional synapses. Together, our findings provide new mechanistic insight into how genetic deficits in TRIO can lead to early neuronal network formation by directly affecting both neurite outgrowth and synapse development.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Animals
  • Autistic Disorder / genetics*
  • Autistic Disorder / metabolism
  • Autistic Disorder / pathology
  • Child
  • Female
  • Gene Expression
  • Guanine Nucleotide Exchange Factors / deficiency
  • Guanine Nucleotide Exchange Factors / genetics*
  • Hippocampus / metabolism
  • Hippocampus / pathology
  • Humans
  • Intellectual Disability / genetics*
  • Intellectual Disability / metabolism
  • Intellectual Disability / pathology
  • Male
  • Mutation*
  • Neurogenesis
  • Neurons / metabolism*
  • Neurons / pathology
  • Primary Cell Culture
  • Protein Serine-Threonine Kinases / deficiency
  • Protein Serine-Threonine Kinases / genetics*
  • Psychomotor Agitation / genetics*
  • Psychomotor Agitation / metabolism
  • Psychomotor Agitation / pathology
  • Rats
  • Sequence Analysis, DNA
  • Severity of Illness Index
  • Synapses / metabolism*
  • Synapses / pathology


  • Guanine Nucleotide Exchange Factors
  • Protein Serine-Threonine Kinases
  • TRIO protein, human