It has been shown that (27) inter-individual differences in morning plasma cortisol levels in individuals of European ancestry are largely attributable to genetic variation in the region of chromosome 14 containing the SERPINA6 and SERPINA1 genes, suggesting that the SERPINA gene exerts an important influence on plasma cortisol levels and may provide clinical insights for future HPA axis adjustments to reduce ADHD symptoms. This evidence concerns the gene SERPINA6 and attention deficit-hyperactivity disorder.