COL2A1 and spondyloepiphyseal dysplasia congenita: As far as we know, more than 500 different variants in COL2A1 have been identified and over 50 variants in COL2A1 are responsible for SEDC, without particular a hot spot variant (BIOBASE Human Gene Mutation Database professional 2019.1, HGMD; http://www.hgmd.cf.ac.uk/ac/index.php; Leiden Open Variation Database 3.0, LOVD 3.0, http://www.lovd.nl/3.0/home).