One major limitation of our study is that although the subjects with PWS in both cohorts were predominantly Caucasians, the North American healthy matched controls included 52% African Americans, who generally have higher plasma levels of AA compared with Caucasians, due to genetic variants (SNP rs174537) in the fatty acid desaturase enzyme that converts linoleic acid to AA [40]. The gene discussed is SCD; the disease is Prader-Willi syndrome.