KRT19 and hydrops fetalis: Though our pilot study was not designed to provide definitive proof for the validity of this hypothesis, our current data suggest that human HF epithelial stem cells are profoundly modulated by spermidine: Spermidine not only upregulates K15 and K19 protein expression in situ (Fig. 4A,D), but intrafollicular spermidine synthesis is also needed for normal K15 expression (Figure 4C).