Mutation Analysis of RUNX2 in Chinese Patients with Cleidocranial Dysplasia

Objective: Cleidocranial dysplasia (CCD) is an autosomal dominant skeletal dysplasia caused by heterozygosity of mutations in human Runx2. The purpose is to identify the spectrum of mutation in Runx2 in Chinese patients with CCD. Methods: In addition to the four families we detected previously, 4 unrelated patients with the clinical diagnosis of CCD were included. DNA was prepared from blood. Exon 0-7 and promoter of the Runx2 Gene were amplified by PCR. We predicted function of a novel mutation by molecular modeling method. Results: We identified a total of 4 mutations, a 63-68Del18bp and a polymorphism. The exchange of glutamine for arginine (R225Q) occurred in 3 patients of one family. The other mutation is R193X in exon2. We also detected a variation of 63-68 Del18bp in exon1, which was predicated delete 6 alanine in QA domain of the protein. In addition to these mutations, we detected 2 novel mutations and 1 polymorphism. An insertion (1198-1199ins A) and a novel polymorphism in promoter region (-332, G→T) was detected in a patient. Another novel mutation L136p causes the leucine at position 36 of the Runt domain to change to pronine (L136p). L36 does not establish DNA contacts. Computer modeling indicated that the L136p mutant showed a reduction in binding activity compared to the wild-type runt domain, suggesting impairment of the activating proper ties of the protein on targeted promoters. We evaluated the clinical features in the patients and compared them with the different mutations identified. There were no differences in severity of phenotype among patients with and without RUNX2 mutations. Conclusion: Mutations of R193x, R225Q and 63-68del18bp, 2 novel mutations(1198-1199ins A,and L136P)and 1 polymorphism were detected. Computer modeling showed that the mutant of L136P caused a reduction in binding activity. There were no the difference in severity of phenotypes and genotypes.