Phenotype Characterization of HD Intermediate Alleles in PREDICT-HD

Area of Science:

• Genetics
• Neuroscience
• Neurology

Background:

• Huntington disease (HD) is a neurodegenerative disorder linked to CAG repeat expansion on chromosome 4.
• Pathology severity correlates with CAG repeat length.
• Previous research indicated subtle motor, cognitive, and behavioral differences in intermediate allele (IA) carriers.

Purpose of the Study:

• To investigate baseline and longitudinal differences in motor, cognitive, behavioral, functional, and imaging outcomes.
• To compare individuals with normal (≤26), intermediate (27-35), and reduced penetrance (36-39) CAG repeat ranges.
• To analyze differences across various outcome measures in Huntington disease genetics.

Main Methods:

• Longitudinal data from 389 participants were analyzed.
• Participants were categorized into normal controls (NC, n=280), intermediate allele (IA, n=21), and reduced penetrance (RP, n=88) groups.
• Linear mixed models were employed to assess baseline and longitudinal outcome differences.

Main Results:

• The best fitting model for most outcomes indicated no baseline or longitudinal differences between NC and IA groups.
• Trends of declining performance were observed with increasing CAG repeat length.
• Some variables showed best fitting models with baseline or longitudinal differences, but not consistently between NC and IA groups.

Conclusions:

• No significant evidence supported distinct differences between the intermediate allele (IA) group and normal controls (NC).
• The study's conclusions regarding the IA group are limited by a small sample size (n=21).
• Further research with larger IA cohorts is needed to confirm these findings in Huntington disease.