Jansen's metaphyseal chondrodysplasia

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Jansen's metaphyseal chondrodysplasia
Synonyms Jansen-type metaphyseal chondrodysplasia, Jansen metaphyseal dysostosis, Jansen disease
Autosomal dominant - en.svg
Jansen's metaphyseal chondrodysplasia is inherited in an autosomal dominant manner.

Jansen's metaphyseal chondrodysplasia (JMC) is a disease that results from ligand-independent activation of the type 1 (PTHR1) of the parathyroid hormone receptor, due to one of three reported mutations (activating mutation).

JMC is extremely rare, and as of 2007 there are fewer than 20 reported cases worldwide.


Blood levels of parathryoid hormone (PTH) are undetectable, but the mutation in the PTHR1 leads to auto-activation of the signaling as though the hormone PTH is present. Severe JMC produces a dwarfing phenotype, or short stature. Examination of the bone reveals normal epiphyseal plates but disorganized metaphyseal regions. Hypercalcemia (elevated levels of calcium in the blood) and hypophosphatemia (reduced blood levels of phosphate), and elevated urinary calcium and phosphate, are generally found in JMC. The absence of hypercalcemia does not eliminate the disease from consideration.

Physical irregularities often associated with Jansen's include: prominent or protruding eyes, a high-arched palate, micrognathia or abnormal smallness of the jaws – particularly the lower (mandible) jaw, choanal stenosis, wide cranial sutures and irregular formation of the long bones which can resemble rickets. Nephrocalcinosis (accumulation of calcium in the interstitum of the kidney) is seen commonly as well.


Jansen's metaphyseal chondrodysplasia is caused by a mutation in the PTHR1 gene. Most cases are due to a spontaneous mutation. Inheritance is autosomal dominant.[1]


Diagnosis typically occurs during infancy or early childhood and is based around physical characteristics and symptoms. X-rays may reveal abnormal development of the bulbous ends of the metaphyses of the limb bones. Tests that detect hypercalciuria and hypercalcaemia are also helpful in the diagnosis.[1]


There is no known treatment at present, although some investigators have tried to lessen the hypercalcemia with various forms of bisphosphonates.


It is named for Murk Jansen (1867–1935), a Dutch orthopedic surgeon.[2][3]


  1. ^ a b "Jansen Type Metaphyseal Chondrodysplasia - NORD (National Organization for Rare Disorders)". NORD (National Organization for Rare Disorders). Retrieved 2018-03-16. 
  2. ^ Jansen, M. Ueber atypische Chondrodystrophie (Achondroplasie) und ueber eine noch nicht beschriebene angeborene Wachstumsstoerung des Knochensystems: Metaphysaere Dysostosis. Z. Orthop. Chir. 61: 253-286, 1934.
  3. ^ Silverthorn KG, Houston CS, Duncan BP (1987). "Murk Jansen's metaphyseal chondrodysplasia with long-term followup". Pediatric radiology. 17 (2): 119–123. doi:10.1007/BF02388087. PMID 3562109. 

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