Disruption of ALX1 causes severe facial clefting and microphthalmia in FND3 patients, whereas loss of function mutations in ALX3 and ALX4 underlie the milder FND1 and FND2 syndromes, respectively (Kayserili et al., 2009; Twigg et al., 2009; Uz et al., 2010; Pini et al., 2020). Here, ALX4 is linked to microphthalmia.