Interestingly, a few of the surviving SHP2Prrx1KO mice developed localized hypertrichosis on the forelimbs and hind limbs (Fig. 1a, bottom), which has been reported to be related to increased SOX9 expression in the hair follicle.44 Alcian blue and Alizarin Red staining of the skeletons in the mutants revealed split sternums, short appendicular bones and short tracheas (Fig. 1b). Here, SOX9 is linked to hypertrichosis.