Novel Mutations of the Cathepsin K Gene in Patients with Pycnodysostosis and Their Characterization

• Published in: The journal of clinical endocrinology and metabolism 2000-01, Vol.85 (1), p.425-431
• Main Authors: Fujita, Yoshi, Nakata, Ken, Yasui, Natsuo, Matsui, Yoshito, Kataoka, Eiichiro, Hiroshima, Kazuo, Shiba, Ryo-ichi, Ochi, Takahiro
• Format: Article
• Language: English
• Subjects: Adult; Amino Acid Substitution; Animals; Biological and medical sciences; Blotting, Western; Bone and Bones - abnormalities; Cathepsin K; Cathepsins - genetics; COS Cells; Diseases of the osteoarticular system; DNA - genetics; DNA - isolation & purification; Epitopes - genetics; Female; Humans; Immunohistochemistry; Male; Malformations and congenital and or hereditary diseases involving bones. Joint deformations; Medical sciences; Middle Aged; Mutation - genetics; Osteosclerosis - congenital; Osteosclerosis - genetics; Pedigree; Protein Sorting Signals - genetics; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger - genetics; RNA, Messenger - isolation & purification
• ISSN: 0021-972X; 1945-7197
• DOI: 10.1210/jcem.85.1.6247

Pycnodysostosis is a rare autosomal recessive skeletal dysplasia characterized by short stature, osteosclerosis, acroosteolysis, bone fragility, and skull deformities. Recently, mutations in the gene encoding cathepsin K (CK), a lysosomal cysteine protease localized exclusively in osteoclasts, were found to be responsible for this disease. We analyzed genomic DNA from four unrelated Japanese patients with this disorder and identified three different mutations of their CK genes: a previously reported missense mutation (A277 V), a novel single base deletion mutation (531 del T) causing a frame shift from codon 142 that results in a premature termination codon, and a novel missense mutation (L9P) in the signal peptide region. To investigate whether the L9P mutation disrupts signal peptide function and decreases protein synthesis, mutant and wild-type CK complementary DNAs driven by the cytomegalovirus promoter were transfected into COS-7 cells, and their gene products were detected by immunohistochemistry and Western blotting. Expression of the mutant protein was markedly reduced, suggesting decreased mature CK production in this patient, which may have been due to dysfunction of the signal peptide. These results provide evidence that a structural change in the signal peptide of the CK protein was involved in the pathogenesis of pycnodysostosis.