Pycnodysostosis

Nature

Pycnodysostosis (from Greek: πυκνός (puknos) meaning "dense", dys ("defective"), and ostosis ("condition of the bone")), is a lysosomal storage disease of the bone caused by a mutation in the gene that codes the enzyme cathepsin K. It is also known as PKND and PYCD.

Source: Wikipedia

Type 
(G) Very specific problems