Genotype-phenotype correlations of GFAP variants in type I Alexander disease subtypes

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Alexander disease (AxD) is a rare, progressive leukodystrophy linked to Glial Fibrillary Acidic Protein (GFAP) gene variants.
• Type I AxD exhibits variable progression, necessitating sub-classification into subtypes Ia, Ib, Ic, and Id.
• Understanding genotype-phenotype correlations is crucial for predicting disease trajectory.

Purpose of the Study:

• To investigate genotype-phenotype correlations in Type I Alexander disease across its clinical subtypes (Ia-Id).
• To identify specific GFAP variants associated with disease progression and ambulation milestones.
• To explore the functional impact of GFAP variants on intermediate filament assembly.

Main Methods:

• Analyzed a cohort of 74 genetically confirmed Type I AxD patients, categorized by subtypes Ia-Id.
• Explored genotypic-phenotypic correlations, stratifying by independent ambulation achievement.
• Performed in vitro assays to assess the assembly of selected mutant GFAP proteins.

Main Results:

• Observed a decrease in GFAP allelic heterogeneity from subtype Ia to Id.
• GFAP variants in exon 1 correlated with milder forms, while exon 4 mutations indicated severe phenotypes.
• Specific variants at p.R239 and p.R79 residues showed distinct trends across subtypes and correlated with ambulation ability.

Conclusions:

• Specific GFAP variants may predict disease progression in Type I AxD.
• These findings support improved patient sub-classification and personalized management strategies.
• Considering genetic and clinical factors is vital for advancing AxD therapeutics.