The presence of germ line mosaicism in cleidocranial dysplasia.

Cleidocranial dysplasia (CCD) is typically an autosomal dominant condition. The possibility of alternative causes, such as an autosomal recessive form or germ line mosaicism, have been suggested in some families with CCD, but not proven. We present a family consisting of a mother having three sons affected with CCD. One of the affected boys is a half brother to the other two affected children. The diagnosis of CCD was confirmed by DNA analysis of the RUNX2 gene in all three of the boys in blood; however, initial DNA testing in the mother's blood did not detect the presence of a RUNX2 mutation in the mother. Further testing through heteroduplex analysis applying high-resolution melting analysis followed by subcloning detected low-level mosaicism in DNA isolated from maternal blood and buccal swab, confirming low-level mosaicism in somatic cells. We present the first case of confirmed germ line mosaicism in CCD.

Sequence and structure of the mouse connexin45 gene.

The connexin45 (Cx45) gene was cloned from a mouse genomic Bacterial Artificial Chromosome library. Approximately 8.4 kb of the genomic DNA was sequenced, and the structure of the Cx45 gene was determined. The mouse Cx45 gene is composed of 3 exons, with the entire coding sequence contained within exon III (EMBL Accession Number AJ300716). This structure is unique for the Cx45 gene, since all other members of the connexin family have only two exons. In addition, computer analysis reveals a potential TATA box and two putative AP-1 binding sites in the 5' region of the gene. Sequence alignment with connexin43 indicates substantial homology in the intronic sequences upstream of the 3' exons of the two genes, suggesting that the Cx45 gene is inherently similar to the rest of the connexin family, and that it probably evolved from an ancestor common to the other connexins.