PDE4D and developmental disability: On the other hand, in the study of Lee et al. all patients (three with PDE4D and two with PRKAR1A mutations) had midface hypoplasia and there were no differences in developmental disability according to the gene affected (among those with PDE4D mutations, one was not affected, a second was mildly affected and a third was significantly affected; whereas both patients with PRKAR1A mutations had mild developmental disabilities) [49].