For example, studies performed on autopsied human brain tissue revealed that ornithine decarboxylase, which is a key regulatory enzyme of PA biosynthesis, showed that, in the case of AD, the mean ornithine decarboxylase levels were significantly upregulated in the temporal cortex, lowered in the occipital cortex and un-changed in hippocampus; this was also in line with animal studies. The gene discussed is ODC1; the disease is Alzheimer disease.