Relationship Between Neurologic Symptoms and Signs and FMR1 Genotype in Premutation Carriers

Area of Science:

• Neurogenetics
• Molecular Neurology

Background:

• Fragile X-associated Tremor/Ataxia Syndrome (FXTAS) is a late-onset neurodegenerative disorder caused by FMR1 gene premutations with expanded CGG repeats (55-200).
• FXTAS clinical features include ataxia, tremor, cognitive decline, and Parkinsonism, linked to white matter degeneration.
• Pathophysiology involves FMR1 mRNA elevation and repeat-associated non-AUG (RAN) translation, impacting CGG-binding proteins.

Purpose of the Study:

• To investigate the relationship between molecular predictors (CGG repeat length, FMR1 mRNA levels) and neurological manifestations in FMR1 premutation carriers.
• To analyze these correlations in individuals with isolated symptoms and those meeting FXTAS diagnostic criteria.

Main Methods:

• 176 FMR1 premutation carriers (111 male, 65 female) were categorized into asymptomatic, non-syndromic with isolated changes, and syndromic FXTAS groups.
• CGG repeat length and FMR1 mRNA expression levels were correlated with neurological and cognitive examination data.

Main Results:

• A consistent association was found between genomic markers (CGG size, FMR1 mRNA) and neurological severity rankings, and FXTAS status.
• Parkinsonism and cognitive impairment showed significant correlation with CGG size, particularly in male carriers.
• A linear relationship was observed between FMR1 CGG size, mRNA levels, and both syndromic and non-syndromic neurological manifestations.

Conclusions:

• FMR1 CGG size and mRNA levels are reliable molecular predictors of neurodegenerative processes in premutation carriers.
• These findings support a continuum of neurodegeneration linked to FMR1 premutations, manifesting across syndromic and non-syndromic forms.
• The study highlights the age-related persistence of these premutation-linked neurodegenerative aspects.