Exonic sequences were examined for all variants independent of the frequency in all 16 known genes responsible for the development of osteopetrosis, including the recently identified SLC4A2 [24], and related disorders with high bone mass (SOST: sclerosteosis, CTSK: pycnodysostosis, LRP5/6: high bone mass). The gene discussed is SOST; the disease is pycnodysostosis.