Final answer:
Huntington's disease is an example of a synaptogenesis/dendritic spine defect. It is caused by a mutation in the gene that encodes the huntington protein, leading to dysregulation in the expression of NMDA receptors.
Step-by-step explanation:
An example of a synaptogenesis/dendritic spine defect is observed in Huntington's disease, a neurodegenerative disorder. In this condition, there is a loss of GABAergic medium-sized spiny neurons, which results in physical, psychological, and cognitive symptoms. The cause of the disease is a mutation in the gene that encodes the huntington protein, leading to dysregulation in the expression of NMDA receptors at synapses and extrasynaptic locations.