A CGA to CAA point mutation resulting in an arginine to glutamine substitution at residue 272 (R272Q) was introduced into exon 8. A loxP-flanked neomycin selection cassette was inserted in the intron downstream of exon 8 and was removed via cre-mediated recombination. The R272Q loss-of-function mutation has been identified as the causative mutation for endocrine-cerebro-osteodysplasia syndrome in humans.