A mutation in PAK3 with a dual molecular effect deregulates the RAS/MAPK pathway and drives an X-linked syndromic...

Area of Science:

• Genetics
• Neuroscience
• Molecular Biology

Background:

• Mutations in PAK3 gene are linked to non-syndromic X-linked intellectual disability (NS-XLID).
• PAK3 plays a crucial role in regulating dendritic spine density and morphology, essential for cognitive function.

Purpose of the Study:

• To identify the genetic cause of a syndromic form of intellectual disability in a three-generation family.
• To characterize the molecular mechanism underlying the novel PAK3 mutation's effect on brain development and signaling pathways.

Main Methods:

• Linkage analysis and whole exome sequencing to identify the genetic variant.
• Biochemical assays to assess PAK3 kinase activity and protein stability.
• In vitro and in vivo studies using zebrafish embryos to investigate functional consequences.

Main Results:

• A novel variant (Lys389Asn) in PAK3 was identified in affected males, abolishing kinase activity.
• The mutation resulted in a dominant-negative effect, leading to increased protein stability and uncontrolled kinase-independent function.
• Aberrant PAK3 function perturbed MAPK signaling, causing alterations in cerebral and craniofacial structures in zebrafish embryos.

Conclusions:

• The study expands the phenotypic spectrum of PAK3 mutations, linking a novel variant to syndromic intellectual disability.
• A dual molecular mechanism involving both kinase-dependent and independent functions of PAK3 underlies the observed phenotype.
• Aberrant PAK3 function directly impacts MAPK signaling, highlighting its critical role in neurodevelopment.