For this, we used the organ culture of microdissected, healthy human scalp HFs (Langan et al, 2015) as a uniquely instructive model system for both identifying novel controls of human HF pigmentation (Gáspár et al, 2011; Samuelov et al, 2013; Hardman et al, 2015; Chéret et al, 2020; Nicu et al, 2021; Tiede et al, 2021) and for interrogating the functions of mTORC1 and TSC2 in human organ physiology. The gene discussed is TSC2; the disease is Hand-foot syndrome.