Several classical genetic markers such as SOX2 (Saxena et al., 2019), LEF1 (Boras-Granic et al., 2006), SOX9 (Nguyen et al., 2018), and KRT15 (Miyachi et al., 2018) have been established as critical genes involved in each step of morphogenesis, and studies on these genes have enabled a fine-toothed dissection of the cellular and molecular dynamics of HF morphogenesis (Sennett et al., 2015; Tomann et al., 2016). Here, SOX9 is linked to hydrops fetalis.