OBJECTIVE: To identify the molecular basis of Papillon-Lefèvre syndrome in two Chinese families.
METHODS: Peripheral blood and mouth swab samples were obtained, from which genomic DNA and RNA were isolated. Sanger sequencing was employed to identify the mutations. mRNA expression was tested by real-time quantitative PCR. Evolutionary conservation, pathogenicity prediction and impact of protein structures of the mutations were conducted with bioinformatics tools and homology modelling. HEK293 cells were transfected with plasmids expressing wild-type or mutated CTSC. CTSC protein expression level and enzyme activity were explored.
RESULTS: Mutation analysis revealed two novel compound heterozygous mutations, the c.190-191insA and c.1211-1212delA in patient 1 and the c.716A>G and c.757+1G>A in patient 2. In both patients, the levels of CTSC mRNA were significantly lower than in their relatives. Homology modelling analysis predicted that the mutations affect the structure and stability of the protein, and in vitro study showed that the CTSC proteins containing the mutations c.190-191insA and c.1211-1212delA, which result in truncated versions of protein, display impaired enzyme activity. The protein containing c.716A>G mutation showed quite similar enzyme activity compared to wild-type CTSC.
CONCLUSIONS: Our data support the molecular mechanism of PLS and enlarge the scope of CTSC gene mutations related to PLS.