In our previous study, we found that an intrabody can be expressed in neurons and reduce the cytotoxicity of N‐terminal mutant HTT in HD mice via intra‐brain injection.[14c] We recently identified that the last 23 amino acids of the C‐terminus of the heavy chain of our published intrabody are able to bind mHTT and we named it smaller intrabody 3 (SM3). This evidence concerns the gene HTT and Huntington disease.