Two microcephaly-associated novel missense mutations in CASK specifically disrupt the CASK-neurexin interaction

Area of Science:

• Genetics
• Neuroscience
• Molecular Biology

Background:

• X-linked CASK gene mutations cause intellectual disability (ID), microcephaly, and pontine-cerebellar hypoplasia (MICPCH).
• The CASK-Tbr-1 interaction was hypothesized to be the molecular cause of MICPCH.
• Missense CASK variants are usually asymptomatic in females.

Purpose of the Study:

• To investigate the molecular basis of CASK-linked MICPCH.
• To test the hypothesis that CASK-Tbr-1 interaction disruption causes MICPCH.
• To examine the functional impact of specific CASK missense mutations (M519T, G659D) on protein interactions and disease phenotypes.

Main Methods:

• Analysis of three girls with heterozygous CASK missense mutations (M519T, G659D).
• In vitro assessment of CASK protein binding to neurexin for M519T and G659D variants.
• Evaluation of CASK G659D protein aggregation and its impact on intramolecular domain interactions.

Main Results:

• The CASK M519T mutation prevents neurexin binding, highlighting the CASK-neurexin interaction's importance.
• The CASK G659D mutation increases protein aggregation and disrupts the PDZ-SH3 domain interface, inhibiting neurexin binding.
• Unlike other aggregation-prone mutations, G659D leads to MICPCH, suggesting neurexin interaction disruption is key.

Conclusions:

• Disruption of the CASK-neurexin interaction, not CASK-Tbr-1, is the likely cause of microcephaly and cerebellar hypoplasia in MICPCH.
• Functional validation of CASK variants is crucial for accurate classification and understanding disease mechanisms.
• These findings refine the understanding of genetic causes for ID and related developmental disorders.