For example, R6/1 heterozygous transgenic mouse model, one of the most widely used HD models, which overexpresses the first exon of human huntingtin with approximately 115 polyQ repeats, show deficits in hippocampal LTP at 5 weeks of age [74], well before the onset of motor deficits and striatal neuron loss observed at 12 weeks of age [75, 76]. This evidence concerns the gene HTT and Huntington disease.