Jansen's metaphyseal chondrodysplasia

Jansen's metaphyseal chondrodysplasia or JMC is a disease that results from ligand-independent activation of the type 1 of the parathyroid hormone receptor

Parathyroid hormone receptor

There are two known parathyroid hormone receptors in mammals termed PTH1R and PTH2R. These receptors bind parathyroid hormone and are members of the GPCR family of transmembrane proteins....

(PTHR1), due to one of three reported mutations (activating mutation).

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

Presentation

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 was present. Severe JMC produces a dwarfing phenotype

Phenotype

A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

, or short stature. Examination of the bone reveals normal epiphyseal plate

Epiphyseal plate

The epiphyseal plate is a hyaline cartilage plate in the metaphysis at each end of a long bone...

s but disorganized metaphyseal regions. Hypercalcemia (elevated levels of calcium in the blood) )and hypophosphatemia

Hypophosphatemia

Hypophosphatemia is an electrolyte disturbance in which there is an abnormally low level of phosphate in the blood. The condition has many causes, but is most commonly seen when malnourished patients are given large amounts of carbohydrates, which creates a high phosphorus demand by cells,...

(reduced blood levels of phosphorus), and elevated urinary calcium and phosphorus 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, choana

Choana

Choana is the posterior nasal aperture.The choanae are separated by the vomer.- Boundaries :It is the opening between the nasal cavity and the nasopharynx....

l stenosis

Stenosis

A stenosis is an abnormal narrowing in a blood vessel or other tubular organ or structure.It is also sometimes called a stricture ....

, wide cranial sutures

Cranial sutures

*Surgical suture, to describe stitches and other techniques for holding tissues together.* Geology, to describe a certain type of boundary between layers of rock....

and irregular formation of the long bones which can resemble rickets

Rickets

Rickets is a softening of bones in children due to deficiency or impaired metabolism of vitamin D, magnesium , phosphorus or calcium, potentially leading to fractures and deformity. Rickets is among the most frequent childhood diseases in many developing countries...

. Nephrocalcinosis

Nephrocalcinosis

Nephrocalcinosis, once known as Albright's calcinosis after Fuller Albright, is a term originally used to describe deposition of calcium salts in the renal parenchyma due to hyperparathyroidism. It is now more commonly used to describe diffuse, fine, renal parenchymal calcification on radiology...

(accumulation of calcium in the interstitum of the kidney) is seen commonly as well.

Treatment

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

Synonyms

Murk Jansen Type Metaphyseal Chondrodysplasia
Jansen Metaphyseal Dysostosis
Jansen Disease
JMC

External links

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