CXCR4 and hydrops fetalis: Based on the interaction between SDF1/CXCR4 signaling and Wnt/β-catenin in some cancer cells and neural progenitors [24–26] and the important role in HF initiation as well as primary hair placode maintenance of Wnt/β-catenin signaling pathway, we hypothesize that SDF1 may participate in HF regeneration by regulating Wnt/β-catenin signaling.