The ethnic background of these families was as follows: northern European (two), Czech, Spanish, Portuguese (two), Indian, and Honduran. Genomic DNA was extracted from blood leukocytes using the Puregene Genomic DNA Isolation kit (Gentra Systems, Minneapolis, Minnesota). Exons 2–8 of the cathepsin K gene (14) were amplified from genomic DNA of Pycno patients by PCR, isolated, and sequenced by cycle sequencing with an ABI 377 Sequencer (Perkin-Elmer Corp., Norwalk, Conneticut, USA).