A Glutamine Repeat Variant of the RUNX2 Gene Causes Cleidocranial Dysplasia.

Cleidocranial dysplasia (CCD), an autosomal dominant skeletal dysplasia characterized by hypoplastic clavicles and delayed closure of the cranial sutures, is caused by mutations of the runt-related transcription factor 2 (RUNX2) gene. The RUNX2 gene consists of a glutamine and alanine repeat domain (Q/A domain, 23Q/17A), a DNA-binding Runt domain and a proline/serine/threonine-rich domain. We report on a familial case of CCD with a novel mutation within the Q/A domain of the RUNX2 gene, which is an insertion in exon 1 (p.Q71_E72insQQQQ) representing the Q-repeat variant (27Q/17A). Functional analysis of the 27Q variant revealed abolished transactivation capacity of the mutated RUNX2 protein. This is the first case report that demonstrated a glutamine repeat variant of the RUNX2 gene causes CCD.