Among CD200+ HF cells, the CD34+ population represents the bulge cells (the stem cell area), and CD34– cells represent the upper HFs, which are further divided into EpCAM+ Sca1+ infundibulum (the HF opening) and EpCAM+ Sca1– isthmus (narrowing portion of the HFs below the infundibulum and above the bulge) (Sakamoto et al., 2021). The gene discussed is CD200; the disease is hydrops fetalis.