Genetic Analysis For Two Cleidocranial Dysplasia Families

Backgrounds:Cleidocranial dysplasia (CCD, MIM 119600) is a rare hereditary skeletal disorder. Its disease rate at birth is about 1:100 000. CCD is a dominantly inherited disease and the locus has been mapped to chromosome 6q21. Previous study shows that heterozygous mutations including insertions and deletions are the main cause of CCD. Besides, CCD shows strong penetrance and apparente familial aggregation. There is no obvious difference between male and female patients. CCD is characterized by patent fontanelles, wide cranial sutures, hypoplasia of clavicles, short stature, supernumerary teeth, and other skeletal anomalies. These skeletal anomalies may cause both mentally and physically prodigious pains.Objective:To further explore the molecular pathogenesis of cleidocranial dysplasia by gene mutation studying of the two collected CCD pedigrees.Methods:A sporadic patient and a four-generation family with the clinical diagnosis of cleidocranial dysplasia was investigated in this study. Genomic DNA was extracted from peripheral blood samples of each selected family member. Direct sequencing of the PCR products of the coding region of RUNX2 gene was used to identify the mutations. We used denaturing high-performance liquid chromatography (DHPLC) to exclude the possibility of happening of the sequenced mutation in unrelated normal individuals. And then detections of fluorescence in situ hybridization (FISH) and whole genome copy number analysis were applied on those patients whose sequenced region was wild type.Results:In each patient of the four-generation pedigree 1, a de novo heterozygous point mutation, cDNA 507 del C, was detected in RUNX2 exon 2. And a 3.5Mb large heterozygous deletion including the whole region of RUNX2 was firstly indicated on the sporadic patient of pedigree 2 through FISH, and then determined by CNV analysis.Conclusions:The sequenced heterozygous point mutation c.507delC in pedigree 1 caused a premature termination in RUNX2 protein. And in pedigree 2, the detected 3.5Mb large deletion caused a complete loss of RUNX2 function. These two novel genome variations are respectively etiological factors of two pedigrees. The identification of the novel mutations further expands the mutation spectrum, and will contribute to prenatal molecular diagnosis and preimplantation genetic diagnosis.