Mutations in the TRAPP complex subunit 2 (TRAPPC2) cause X-linked spondyloepiphyseal dysplasia tarda, while mutations in the TRAPP complex subunit 9 (TRAPPC9) cause postnatal mental retardation with microcephaly. This evidence concerns the gene TRAPPC2 and spondyloepiphyseal dysplasia tarda, X-linked.