FAM20C and desmosterolosis: Other forms of neonatal osteosclerosis include Blomstrand dysplasia (MIM215045), due to autosomal recessive inactivating mutations in PTHR1 which codes for the PTH/PTHrP receptor 1, and which is usually lethal; desmosterolosis (MIM602398), due to autosomal recessive mutations in DHCR24 which codes for 3‐beta‐hydroxysterol delta‐24‐reductase, with mutations resulting in impaired sterol‐metabolism; and Raine dysplasia (MIM259775), due to autosomal recessive FAM20C mutations coding for Dentin matrix protein 4, which can also be lethal.