The molecular bases of Alzheimer\u27s disease (AD) remain unclear. We used a lipidomic approach to identify lipid abnormalities in the brains of subjects with AD (N = 37) compared to age-matched controls (N = 17). The analyses revealed statistically detectable elevations in levels of non-esterified monounsaturated fatty acids (MUFAs) and mead acid (20:3n-9) in mid-frontal cortex, temporal cortex and hippocampus of AD patients. Further studies showed that brain mRNAs encoding for isoforms of the rate-limiting enzyme in MUFAs biosynthesis, stearoyl-CoA desaturase (SCD-1, SCD-5a and SCD-5b), were elevated in subjects with AD. The monounsaturated/saturated fatty acid ratio (\u27desaturation index\u27)--displayed a strong negative correlation with measures of cognition: the Mini Mental State Examination test (r = -0.80; P = 0.0001) and the Boston Naming test (r = -0.57; P = 0.0071). Our results reveal a previously unrecognized role for the lipogenic enzyme SCD in AD
