An R83W mutation in Rab3A causes autosomal-dominant cerebellar ataxia

Area of Science:

• Neurogenetics
• Molecular Neuroscience
• Cell Biology

Background:

• Spinocerebellar ataxias (SCAs) encompass over 40 genes, leading to progressive neurodegeneration.
• The specific genetic and molecular underpinnings of many SCAs remain incompletely understood.
• Rab3A, a small GTPase, is crucial for regulated exocytosis and synaptic vesicle trafficking.

Purpose of the Study:

• To investigate the role of a novel RAB3A variant in spinocerebellar ataxia.
• To elucidate the functional consequences of the identified RAB3A mutation on protein interactions and cellular localization.
• To explore the potential pathomechanisms of SCA linked to Rab3A dysfunction.

Main Methods:

• Genetic analysis of two families with cerebellar ataxia to identify causative variants.
• In vitro functional assays (GTP-binding, effector binding) using the identified Rab3A mutant.
• Cellular localization studies in PC12 cells to compare mutant vs. wild-type Rab3A.
• Immunohistochemical analysis of Rab3A localization in human cerebellum.

Main Results:

• Identified the c.247C>T p.(Arg83Trp) variant in RAB3A in two families with adult-onset cerebellar ataxia.
• The R83W mutation impairs Rab3A's interaction with key effectors RIM1 and Rabphilin-3A.
• Mutant Rab3A R83W exhibits mislocalization to the cytoplasm, unlike wild-type Rab3A.
• Rab3A is localized to presynaptic terminals in the cerebellum, suggesting a role in synaptic function.

Conclusions:

• The RAB3A R83W variant is pathogenic and causes a form of spinocerebellar ataxia.
• Disruption of Rab3A-effector interactions underlies the observed neurodegeneration.
• Presynaptic dysfunction at parallel fiber-Purkinje cell synapses is a likely mechanism of disease pathogenesis.