Normalized Clinical Severity Scores Reveal a Correlation between X Chromosome Inactivation and Disease Severity in...

Area of Science:

• Genetics
• Neuroscience
• Developmental Biology

Background:

• Rett Syndrome (RTT) is a severe neurodevelopmental disorder caused by mutations in the MECP2 gene.
• X-chromosome inactivation (XCI) leads to mosaic expression of MECP2 alleles, potentially influencing RTT severity.
• Previous studies faced challenges correlating XCI with RTT severity due to confounding age and MECP2 genotype effects.

Purpose of the Study:

• To develop an age- and genotype-normalized measure of RTT severity.
• To investigate the relationship between XCI and RTT clinical severity, accounting for MECP2 genotype.

Main Methods:

• Longitudinal data from the US Rett Syndrome Natural History Study was modeled.
• A normalized clinical severity score was created to adjust for age and genotype.
• The normalized score was applied to RTT XCI datasets to assess correlations.

Main Results:

• The developed model accurately reflected age-dependent increases in RTT severity.
• A genotype-dependent correlation between XCI and RTT severity was identified.
• XCI influenced disease severity only in individuals with MECP2 variants linked to increased clinical severity.

Conclusions:

• A novel normalized RTT severity score effectively mitigates age and genotype confounds.
• XCI's impact on RTT severity is specific to the underlying MECP2 genotype.
• This normalized measure facilitates the discovery of additional RTT severity factors.