Jansen's metaphyseal chondrodysplasia
Jansen's metaphyseal chondrodysplasia is currently classified as an "extremely rare" disorder, with just 20 medically documented reported cases on record to date. Jansen metaphyseal chondrodysplasia is sometimes also called simply Jansen disease. It is also called Jansen's metaphyseal dysostosis and Murk Jansen type metaphyseal chondrodysplasia.
Definition & Facts
One of the chief symptoms, short-limbed dwarfism, often lumps this much rarer condition in with the more than 200 other possible causes for dwarfism. However, there are some additional symptoms that set Jansen's metaphyseal chondrodysplasia apart and must be identified in order to arrive at an accurate diagnosis.
Symptoms & Complaints
- Abnormal (bulbous) limb growths at bone ends.
- Unusually short limbs.
- Short stature.
- Abnormal bone and cartilage development, especially in extremities.
- Bone hardening over time.
- Certain set facial abnormalities that often present at birth. Small jaw, receding chin, high palate, eyes that are spaced widely.
- Wide spacing of cranial joints.
- Clubbed, short fingers.
- Small lower rib cage with predisposition to rib fractures.
- Malformation or curvature of spine (scoliosis) and pelvic region and bowing out of the legs.
- Disproportionate growth of arms and legs to elongated torso.
- Joint swelling and low muscle mass.
- Joint stiffness and fixation of joints.
- Walking while bent-over or hunched and waddling.
- Overgrowth of facial bones.
- Predisposition to blindness and deafness due to skull abnormalities and skull bone hardening (sclerosis).
The cause of Jansen's metaphyseal chondrodysplasia is now known to be from a genetic mutation. The disorder can be either spontaneous or heritable. When heritable, it is considered autosomal dominant which means that an individual only needs to receive a copy of the mutated gene from one (not both) parents in order to develop the disorder.
Thanks to recent research, some information is now known about the specific gene involved in Jansen's metaphyseal chondrodysplasia. The gene that is most likely a trigger in most cases of the disorder (spontaneous mutation) is within chromosome 3.
The mutation disrupts production of a protein called PTH/PTHrP (parathyroid) receptor. This protein is supposed to regulate how much calcium is in the blood and prevent hypercalcemia. This is important because hypercalcemia is thought to be a cause for many of the symptoms of Jansen's metaphyseal chondrodysplasia.
Diagnosis & Tests
Because the genetic mutation that causes Jansen's metaphyseal chondrodysplasia affects calcium levels, physicians test for calcium levels in both the urine and the blood when Jansen's metaphyseal chondrodysplasia is suspected.
- Clinical urine tests will be conducted to check for hypercalciuria which is high calcium levels in the urine.
- Blood tests will be conducted to detect hypercalcemia which is high calcium levels in the blood.
- X-ray of bones. To look for abnormal, bulbous limb development.
- Imaging tests may be performed as needed to look for other internal abnormalities. Examples include magnetic resonance imaging (MRI) tests and computed tomography (CT) scans.
In addition to genetic testing and the tests described here, doctors still use the symptoms checklist as a diagnostic tool especially as Jansen's metaphyseal chondrodysplasia is progressive and presents worsening symptoms over time that need to be catalogued.
Treatment & Therapy
Treatment for Jansen's metaphyseal chondrodysplasia is primarily related to managing symptoms as they arise. Typically the treatment needs of an affected individual will change and shift as the disease itself progresses, requiring a multi-disciplinary team to coordinate treatment. Team members often include the following medical professionals:
- Speech pathologist.
- Physical therapist.
Surgical treatment can often correct some of the discomfort associated with joint and bone abnormalities as the disease progresses. Physical therapy can also assist with more comfortable movement and increased mobility.
A newer treatment that shows promise is to prescribe bisphosphonates, a class of drugs more typically associated with treating osteoporosis, or brittle bone syndrome. Administering bisphosphonates to individuals with Jansen's metaphyseal chondrodysplasia can help halt the loss of bone mass and stave off bone fractures that commonly occur with the disorder.
Prevention & Prophylaxis