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.

Papillon-Lefevre syndrome is a rare (1-4 cases per million) autosomal recessive disorder showing predominantly oral and dermatological manifestations in the form of aggressive periodontitis affecting both primary and permanent dentition and palmoplantar hyperkeratosis. Genetic studies have shown that mutations in the major gene locus of chromosome 11q14 with loss of function of cathepsin C gene are responsible for Papillon-Lefevre syndrome. This report presents two siblings with classic signs and symptoms of Papillon-Lefevre syndrome. The exact cause for periodontal destruction in patients with Papillon-Lefevre syndrome is not known but it is thought to be due to defect in neutrophil function, immune suppression and mutations in cathepsin C gene.