A rare syndrome with characteristics of palmoplantar hyperkeratosis, severe early-onset periodontitis, onychogryposis, pes planus, arachnodactyly and acroosteolysis. The syndrome presents with severe and extensive skin manifestations. Severe, early-onset progressive periodontitis that affects both the deciduous and permanent dentitions and presents with gingival inflammation and alveolar bone destruction is a hallmark of the disease. Onychogryposis, arachnodactyly, acroosteolysis and pes planus are additional features that help to distinguish from other forms of palmoplantar hyperkeratosis. The syndrome is caused by germline mutations in the lysosomal protease cathepsin C (CTSC) gene mapped to chromosome 11q14.1-q14.3. It is transmitted as an autosomal recessive trait.