The major findings of the present observational study are: 1) AD patients hadsignificantly decreased plasma levels of leptin compared with healthy controls,whereas circulating CD34+ cells were significantly upregulated in ADpatients; 2) in logistic regression analysis, decreased leptin concentration andincreased number of CD34+ cells were both significantly associatedwith the presence of AD; 3) high plasma levels of leptin inversely correlated with alower MMSE score and an advancing age and positively correlated with an increase inBMI. The gene discussed is LEP; the disease is Alzheimer disease.