Multicentric osteolysis, nodulosis, and arthropathy

Multicentric osteolysis, nodulosis, and arthropathy (MONA) describes a rare inherited disease characterized by a loss of bone tissue (osteolysis), particularly in the hands and feet. MONA includes a condition formerly called nodulosis-arthropathy-osteolysis (NAO) syndrome. It may also include a similar disorder called Torg syndrome, although it is unknown whether Torg syndrome is actually part of MONA or a separate disorder caused by a mutation in a different gene.

In most cases of MONA, bone loss begins in the hands and feet, causing pain and limiting movement. Bone abnormalities can later spread to other areas of the body, with joint problems (arthropathy) occurring in the elbows, shoulders, knees, hips, and spine. Most people with MONA develop low bone mineral density (osteopenia) and thinning of the bones (osteoporosis) throughout the skeleton. These abnormalities make bones brittle and more prone to fracture. The bone abnormalities also lead to short stature.

Many affected individuals develop subcutaneous nodules, which are firm lumps of noncancerous tissue underneath the skin, especially on the soles of the feet. Some affected individuals also have skin abnormalities including patches of dark, thick, and leathery skin. Other features of MONA can include clouding of the clear front covering of the eye (corneal opacity), excess hair growth (hypertrichosis), overgrowth of the gums, heart abnormalities, and distinctive facial features that are described as "coarse."