PTH1R and metaphyseal chondrodysplasia, Jansen type: These varying effects of PTH/PTHrP activity are seen in two skeletal dysplasias that result from mutations in PTH1R; Jansen Metaphyseal Chondrodysplasia (JMC) (Cohen, 2002), an autosomal dominant disease that results from constitutive action of PTH1R (Schipani et al., 1995) and Blomstrand Chondrodysplasia (BOCD) (Loshkajian et al., 1997), an autosomal recessive disorder caused by loss-of-function mutations in PTH1R (Jobert et al., 1998).