Huntington disease (HD) is a dominantly inherited disorder caused by a CAG 
expansion mutation in the huntingtin (HTT) gene, which results in the HTT 
protein that contains an expanded polyglutamine tract. The adult form of HD 
exhibits a late onset of the fully symptomatic phase. However, there is also a 
long presymptomatic phase, which has been increasingly investigated and 
recognized as important for the disease development. Moreover, the juvenile form 
of HD, evoked by a higher number of CAG repeats, resembles a neurodevelopmental 
disorder and has recently been the focus of additional interest. Multiple lines 
of data, such as the developmental necessity of HTT, its role in the cell cycle 
and neurogenesis, and findings from pluripotent stem cells, suggest the 
existence of a neurodevelopmental component in HD pathogenesis. Therefore, we 
discuss the early molecular pathogenesis of HD in pluripotent and neural stem 
cells, with respect to the neurodevelopmental aspects of HD.