The Huntingtin protein is the product of the Huntington's disease-associated gene (HTT), with no known family members. Structurally, it contains a polyglutamine region, the function of which is not fully understood. It is widely localized, including in the nucleus and cytoplasm, and participates in biological responses and signaling pathways such as neurodevelopment, endocytosis, and gene transcription. The HTT gene is expressed in various tissues, and its specific expression is crucial for cell survival. Mutations caused by CAG trinucleotide repeat expansion are directly associated with Huntington's disease. These mutations increase the length of the polyglutamine tract, affecting protein function and leading to neurodegeneration.