Mutations in the Pathway that Regulates CDC25 Activity Causes Cleft Lip and Palate

Objectives: To identify genetic mutations that cause cleft lip in a pair of cleft discordant monozygotic twins. The hypothesis was that the twins would be discordant for a mutation that was leading to the involvement of the lip.
Methods: Two female monozygotic twins born with isolated clefts were studied. One twin was born with unilateral left cleft lip with cleft palate whereas the other was born with a submucous cleft palate only. Saliva samples were obtained as a source of genomic DNA. Whole exome sequencing was performed to identify the presence of potentially deleterious mutations. Sanger sequencing was used to independently confirm mutations of interest.
Results: Sanger sequencing validated a nonsense mutation in both of the twins in exon four of the USP29 gene. This mutation in USP29 is hypothesized to inhibit Claspin, a protein in the CDC25 pathway. The binding protein FBP induces USP29 to regulate proliferation and inhibit apoptosis. FBP inducing Claspin enables the down regulator in the CDC25 pathway, p53, to be turned on and function to correct double-strand DNA breaks. We suspected that the twin with cleft lip and more severe cleft palate may have additional mutations in the same pathway. We found one synonymous mutation (rs10770042) in WEE1 in the more severely affected twin who had both the lip and palate completely clefted, that changes the prediction of exonic splicing enhancers abolishing the potential binding of four sequences and creating affinity for a fifth.
Conclusions: Mutations in the CDC25 pathway may lead to isolated forms of cleft lip and palate and the severity of the clefts may be modulated by the presence of additional deleterious mutations in the same pathway.