Some subsequent studies observed unilaterally elevated PS in normal embryos (Yu and Ornitz, 2011; Bush and Jiang, 2012; Liu et al., 2021), and others that observed unilateral elevation in mutant mouse models of cleft palate, including those with Specc1l deficiency (Liu et al., 2008; Hill et al., 2015; Butali et al., 2019; Goodwin et al., 2020; Hall et al., 2020). The gene discussed is SPECC1L; the disease is cleft palate.