Nevertheless, it is instructive to consider the Apert syndrome model, in which the mice are hemizygous for Fgfr2 IIIC and exhibit a splicing switch resulting in ectopic expression of FGFR2 IIIb in calvarial mesenchyme; similar mutations are only rarely found in humans (Hajihosseini et al., 2001, 2009; Bochukova et al., 2009). The gene discussed is FGFR2; the disease is Apert syndrome.