Jansen disease, also known as Jansen type metaphyseal chondrodysplasia, is an extremely rare progressive disorder. Affected individuals show unusually short arms and legs and short stature (short-limbed dwarfism). It occurs because of the portion of the bones of the arms and legs that develop abnormally with unusual cartilage formation and subsequent abnormal bone formation at the large (bulbous) end portions (metaphyses) of these long bones (metaphyseal chondrodysplasia).
Infants with Jansen disease may have some changes and abnormalities in his or her facial features and additional skeletal malformations. Abnormal cartilage and bone development may also affect other bones of the body, particularly those of the hands and feet (i.e., metacarpals and metatarsals).
Affected individuals may begin to show progressive stiffening and swelling of many joints and/or an unusual “waddling gait” and squatting stance, in their childhood. As they grow up, affected adults may eventually develop abnormally hardened (sclerotic) bones especially in the back of the head (cranial bones).In some cases, these may lead or cause blindness and/or deafness. These people have abnormally high levels of calcium in the blood (hypercalcemia)
The variety and severity of symptoms may depend from person to another person. The common cases of Jansen disease are genetic changes.