CAG repeat size in Huntingtin alleles is associated with cancer prognosis

Area of Science:

• Genetics
• Oncology
• Neurogenetics

Background:

• Huntingtin gene (HTT) CAG repeat expansions cause Huntington's disease (HD).
• HTT variants are linked to cancer, with lower incidence in HD patients but accelerated tumor progression in mouse models.
• The dual role of HTT CAG repeats in cancer necessitates further investigation.

Purpose of the Study:

• To explore the relationship between Huntingtin gene (HTT) CAG repeat length and cancer predisposition and progression.
• To analyze HTT CAG repeat sizes in women with BRCA mutations and sporadic breast cancer.
• To determine if HTT CAG repeat length correlates with cancer incidence, age of onset, and metastasis.

Main Methods:

• Genomic DNA analysis of HTT CAG repeat expansions in 2407 women with BRCA1/2 mutations and 431 sporadic breast cancer patients.
• Correlation analysis between HTT CAG repeat length and cancer incidence, age of onset, and metastasis.
• Comparison of HTT CAG repeat prevalence with literature data.

Main Results:

• A higher-than-expected prevalence of pathological HTT CAG expansions was observed.
• In BRCA2 carriers, longer HTT CAG tracts correlated with reduced ovarian cancer incidence.
• In BRCA1 carriers with breast cancer, intermediate HTT alleles (≥27 CAGs) were linked to earlier onset (2.4 years sooner).
• Sporadic HER2+ breast cancer patients showed an 11.10-fold increase in metastasis per 10 additional HTT CAG repeats.

Conclusions:

• HTT CAG repeat length exhibits a complex, paradoxical association with cancer.
• Longer CAG tracts may reduce overall cancer incidence but can also be linked to increased cancer severity, including earlier onset and metastasis.
• These findings highlight the intricate role of HTT genetics in cancer biology.