= marble bone disease, Albers-Schönberg disease

- reduced bone resorption and skeletal sclerosis due to impaired function of osteoclasts- mutation in carbonic anhydrase (CA2) which prevents acidification of the osteoclast resorption pit

Morphology- Erlenmeyer flask deformity- spongiosa filling the medullary cavity, leaving no room for hematopoietic marrow (--> anaemia, extramedullary hematopoiesis)- small neural foramina, which compress exiting nerves (--> cranial nerve deficity like deafness, facial paralysis)

- Severe infantile osteopetrosis: autosomal recessive- mild autosomal dominant form

Therapy: hematopoietic stem cell transplantation (osteoclasts are derived from hematopoietic precursors)