The form of osteopetrosis caused by hypomorphic mutations in theIKBKGgene on the X chromosome; the bone pathology arising from cathepsin K mutations, which is termed pycnodysostosis in humans; and the type of osteopetrosis present in patients with leucocyte adhesion deficiency III, which is caused by mutations in theKINDLIN3gene.33Clinical features34: The more severe forms tend to have autosomal recessive inheritance, while the mildest forms are observed in adults and are inherited in an autosomal-dominant manner. The gene discussed is CTSK; the disease is osteopetrosis.