Clinical-Genetic Associations in the Prospective Huntington at Risk Observational Study (PHAROS): Implications for...

Area of Science:

• Neuroscience
• Genetics
• Clinical Neurology

Background:

• Identifying pre-diagnostic markers for Huntington disease (HD) is critical for early intervention and clinical trial design.
• The cytosine-adenine-guanine (CAG) expansion in the huntingtin gene is the known cause of HD, but its earliest clinical manifestations remain under investigation.

Purpose of the Study:

• To identify the earliest clinical features associated with the motor diagnosis of Huntington disease (HD) in at-risk individuals.
• To understand the progression of motor, cognitive, behavioral, and functional domains in individuals with and without the HD CAG expansion before clinical diagnosis.

Main Methods:

• A prospective, multicenter, longitudinal cohort study (Prospective Huntington at Risk Observational Study [PHAROS]) involving 983 at-risk adults unaware of their mutation status.
• Assessment of Huntington disease mutation status (CAG expansion vs. non-expansion) and longitudinal evaluation of motor, cognitive, behavioral, and functional domains using the Unified Huntington's Disease Rating Scale over up to 10 years.
• Statistical analysis using repeated-measures to assess the divergence of linear trends between expanded and non-expanded groups, adjusting for age and sex.

Main Results:

• Participants with the CAG expansion (35.1%) exhibited significantly more impaired motor, cognitive, and behavioral scores at baseline compared to non-expansion carriers (64.9%).
• Longitudinal analysis revealed significant worsening in motor, cognitive, and functional measures in individuals with CAG expansions compared to those without (P < .001 for all).
• Behavioral domain scores did not show significant divergence between the groups over the study period.

Conclusions:

• Prospectively accrued clinical data indicate that individuals with the Huntington disease CAG expansion experience earlier declines across multiple domains before diagnosis.
• These findings suggest that relatively large treatment effects would be necessary to demonstrate efficacy in randomized, placebo-controlled clinical trials involving premanifest HD individuals.