HD Glossary

Note: Some words can have differing definitions depending on the context in which they are used. The definitions presented here are the ones that best apply to the words as they are used. HDSA is grateful to the Stanford Hopes website for their contribution and maintenance of this glossary.



  • ubiquinone - Another term for coenzyme Q10.
  • ubiquitin - A small molecule that latches onto damaged or mutated proteins in the cell. Ubiquitin acts as a flag indicating that these proteins can be destroyed by proteasomes.
  • ubiquitin-proteasome system (UPS) - A cellular quality control system that tags misfolded proteins for refolding or degradation.
  • UHDRS - The Unified Huntington's Disease Rating Scale, used to provide uniform assessment of the clinical features and progression of HD.
  • unequal crossing over - During meiosis, when the crossing over that takes place between homologous chromosomes is unequal. Instead of entire alleles switching places, only parts of each allele will switch, and these parts are usually unequal in length.
  • unequal crossing over model - A possible model for how repeat expansions occur. Since unequal crossing over can result in chromosomes that differ from their original lengths, this model suggests that unequal crossing over is the cause of extended repeat regions.
  • unsaturated fat - A type of fat found mainly in vegetable oils which, due to its chemical structure, tends to reduce levels of cholesterol and improve cell membrane function.
  • upregulation - A process that increases the responsiveness of a cell by increasing the number of receptors on the cell membrane.
  • UPS - Abbreviation for ubiquitin-proteasome system.
  • uracil - One of the four nitrogenous bases found in RNA; often abbreviated as the letter “U.” It pairs with the base adenine.
  • uterus - The female reproductive organ where the fertilized egg implants and the growing embryo is nourished.