An osteoclast (from Ancient Greek  ὀστέον (osteon) bone, and  κλαστός (clastos) broken) is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodeling of bones of the vertebral skeleton. The osteoclast disassembles and digests the composite of hydrated protein and mineral at a molecular level by secreting acid and a collagenase, a process known as bone resorption. This process also helps regulate the level of blood calcium. Osteoclasts are found on those surfaces of bone which are undergoing resorption. On such surfaces, the osteoclasts are seen to be located in shallow depressions called resorption bays (Howships lacunae). The resorption bays are created by erosive action of osteoclasts on the underlying bone. The border of the lower part of an osteoclast exhibits finger-like processes due to presence of deep infoldings of the cell membrane; this border is called ruffled border. The ruffled border lies in contact with the bone surface within a resorption bay. The periphery of the ruffled border is surrounded by a ring-like zone of cytoplasm which is devoid of cell organelles but is rich in actin filaments. This zone is called clear zone or sealing zone. The actin filaments enable the cell membrane surrounding the sealing zone to be anchored firmly to the bony wall of Howships lacunae. In this way, a closed subosteoclastic compartment is created between the ruffled border and the bone that is undergoing resorption.
Neurofibromatosis type I (NF-1) is a complex multi-system human disorder caused by the mutation of neurofibromin, a gene on chromosome 17 that is responsible for production of a protein which is needed for normal function in many human cell types. NF-1 causes tumors along the nervous system which can grow anywhere on the body. NF-1 is one of the most common genetic disorders and is not limited to any persons race or sex. NF-1 is an autosomal dominant disorder, which means that mutation or deletion of one copy (or allele) of the NF-1 gene is sufficient for the development of NF-1, although presentation varies widely and is often different even between relatives affected by NF-1.As of 2015, there are at least 100,000 people in the U.S. and about 10,000 people in the UK who have been diagnosed with NF. Common symptoms of NF-1 include brownish-red spots in the colored part of the eye called Lisch nodules, benign skin tumors called neurofibromas, and larger benign tumors of nerves called plexiform neurofibromas, scoliosis (curvature of the spine), learning disabilities, vision disorders, mental disabilities, multiple café au lait spots and epilepsy. NF-1 affected individuals also have a much higher rate of cancer and cardiovascular disease than the population in general.NF-1 is a developmental syndrome caused by germline mutations in neurofibromin, a gene that is involved in the RAS pathway (RASopathy).