knock-in By Ivan Suarez Robles 10 Nov, 2010 Refers to an organism that has a particular gene or trait purposely inserted by selective breeding or laboratory techniques (e.g., a huntingtin knock-in mouse).Related Articles: Stem Cell Research Provides Insight on HD Development and Potential Therapeutic TargetsUpdates in HD Research: January-March 2020Impairments of Smell in Huntington’s DiseaseCognitive Training in HDDrs. James Gusella and Marcy MacDonald