Intermediate and Expanded HTT Alleles and the Risk for α-Synucleinopathies.

Area of Science:

• Neurogenetics
• Neurodegenerative Diseases
• Molecular Biology

Background:

• Previous research suggests a correlation between the CAG repeat number in the Huntingtin (HTT) gene and various non-Huntington neurodegenerative diseases.
• The HTT gene, known for its role in Huntington's disease, may influence other neurological conditions.

Purpose of the Study:

• To investigate the association between expanded HTT CAG alleles and the risk of developing alpha-synucleinopathies.
• To determine if HTT CAG allele size modulates the phenotype of alpha-synucleinopathies.
• To explore the role of HTT CAG repeat expansions in Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multisystem atrophy (MSA).

Main Methods:

• Genotyping of the HTT gene CAG repeat number in a case-control series.
• Analysis of APOE-Ɛ isoforms in patients diagnosed with alpha-synucleinopathies (clinically or neuropathologically).
• Comparison of HTT CAG repeat lengths and allele frequencies between patient groups and healthy controls.

Main Results:

• Low-penetrance HTT repeat expansions were found in some Parkinson's disease patients and healthy controls, but not in DLB or MSA patients.
• Increased HTT CAG repeat numbers were observed in DLB and PD groups, influenced by male gender and the APOE4 allele in DLB.
• A higher frequency of HTT intermediate alleles (IAs) was noted in the MSA group compared to controls, with statistically significant differences in neuropathologically confirmed cases. Two MSA patients with HTT CAG IAs showed polyQ inclusions in critical neurodegenerative regions.

Conclusions:

• The study establishes a link between HTT CAG repeat number, HTT IAs, and expanded HTT CAG repeats with non-Huntington's disease neurodegenerative pathologies.
• Findings support the hypothesis that HTT gene variations and alpha-synucleinopathies may share common neurodegenerative pathways.
• HTT CAG repeat expansions represent a potential risk factor or modulator for certain neurodegenerative diseases beyond Huntington's disease.