Analysis of CSF samples revealed significantly lower levels of insulin (Figure 3A), ghrelin (Figure 3C), and GLP-1 (Figure 3D) in subjects with probable AD relative to normal aging, but no significant inter-group differences with respect to leptin (Figure 3B), GIP-1 (Figure 3E), PP (Figure 3F), or PYY (Figure 3G). The gene discussed is PPY; the disease is Alzheimer disease.