In Jansen type metaphyseal chondrodysplasia, an extremely rare progressive disorder, portions of the bones of the arms and legs develop abnormally with unusual cartilage formations and subsequent abnormal bone formation at the large (bulbous) end portions (metaphyses) of these long bones (metaphyseal chondrodysplasia). As a result, affected individuals exhibit unusually Short arms and legs and Short stature (short-limbed dwarfism), findings that typically become apparent during childhood. Abnormal cartilage development and bone formation may also affect other bones of the body, including those of the hands and feet (i.e., metacarpals and metatarsals). As affected individuals age, abnormal cartilage formations in affected areas may harden into rounded (bulbous) masses of bone, which may become prominent.
Most infants with Jansen type metaphyseal chondrodysplasia have characteristic facial abnormalities that are present at birth (congenital) including an unusually Small jaw (micrognathia); receding chin; highly-arched roof of the mouth (palate); unusually wide fibrous joints between bones of the skull (cranial sutures); and/or prominent, widely spaced eyes (ocular hypertelorism).
During childhood, it may become apparent that affected individuals have additional Skeletal abnormalities such as unusually short, clubbed fingers (brachydactyly) with permanent fixation of the fifth finger in a bent position (clinodactyly); an abnormally small lower rib cage; fractured ribs; and/or malformations of the spine and pelvis. As affected children age, they may eventually develop abnormal front-to-back and side-to-side curvature of the spine (kyphoscoliosis) and/or bowing of the legs. In addition, Short stature becomes more obvious as affected children age; the torso grows longer, but the arms and legs do not grow proportionally.
Children with Jansen type metaphyseal chondrodysplasia may also experience diminished muscle mass and gradual Swelling of certain joints, particularly the hips and knees. Affected joints may become stiff and painful and certain movements, particularly bending (flexion), may become limited. Most affected children develop an unusual semi-squatting stance and a “waddling” walk (gait). Eventually, certain joints may become fixed in a permanently bent (flexed) position (joint contractures).
Intellectual disability and a delay in the acquisition of skills requiring coordination of muscular and mental activity (psychomotor retardation) have not been reported in patients with Jansen metaphyseal chondrodysplasia.
Some adults with Jansen type metaphyseal chondrodysplasia may eventually exhibit overgrowth of the bones above the eyes and those of the forehead (supraorbital and frontonasal hyperplasia), an unusually thickened base of the skull, and/or abnormal hardening (sclerosis) of certain cranial bones. In some patients, sclerosis of certain cranial bones may eventually result in Blindness and/or deafness. Affected adults may also exhibit additional joint contractures. In addition, affected individuals have abnormally high levels of calcium in the blood (hypercalcemia). The degree of hypercalcemia may vary in different patients. At least one mild form of Jansen type metaphyseal chondrodysplasia has been identified in which affected family members had less-pronounced skeletal abnormalities.