biology

Jansen's metaphyseal chondrodysplasia

Jansen's metaphyseal chondrodysplasia is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Jansen's metaphyseal chondrodysplasia rather than just read about it. In short: Jansen's metaphyseal chondrodysplasia (JMC) is a disease that results from ligand-independent activation of the type 1 (PTH1R) 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.

Key takeaways

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Reference excerpt

Jansen's metaphyseal chondrodysplasia (JMC) is a disease that results from ligand-independent activation of the type 1 (PTH1R) 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. There are only 2 known families, from Dubai and Texas, in which the disease was passed from mother to daughter (Texas), and from a mother to her 2 sons (Dubai).

Presentation and genetics Blood levels of parathyroid hormone (PTH) are undetectable, but the mutation in the PTH1R 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 renal interstitium) is seen commonly as well.

Clinical features Individuals with JMC typically present with short stature, bowed legs, and widened growth plates. Other features may include hypercalcemia, joint pain, and muscle weakness. The severity of symptoms can vary widely among affected individuals.

Cause Jansen's metaphyseal chondrodysplasia is caused by a mutation in the PTH1R gene. Most cases are due to a spontaneous mutation. Inheritance is autosomal dominant.

Diagnosis 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.

Treatment There is no known treatment at present, although some investigators have tried to lessen the hypercalcemia with various forms of bisphosphonates. Treatment is symptomatic and may include physical therapy, orthopedic interventions, and management of hypercalcemia. Regular monitoring of growth and skeletal development is essential for managing the condition.

Eponym It is named for Murk Jansen (1867–1935), a Dutch orthopedic surgeon.

References

Further reading Metaphyseal chondrodysplasia, Jansen type -- OrphaNet Information (PDF) Archived 2022-05-03 at the Wayback Machine Jansen’s Metaphyseal Chondrodysplasia, Case Report, Indian Pediatrics Jansen Type Metaphyseal Chondrodysplasia -- National Organization for Rare Disorders (NORD) A Novel Parathyroid Hormone (PTH)/PTH-Related Peptide Receptor Mutation in Jansen’s Metaphyseal Chondrodysplasia, The Journal of Clinical Endocrinology & Metabolism (1) Archived 2011-05-16 at the Wayback Machine A Form of Jansen’s Metaphyseal Chondrodysplasia with Limited Metabolic and Skeletal Abnormalities Is Caused by a Novel Activating Parathyroid Hormone (PTH)/PTH-Related Peptide Receptor Mutation, The Journal of Clinical Endocrinology & Metabolism (2) Archived 2011-05-16 at the Wayback Machine Constitutively Activated Receptors for Parathyroid Hormone and Parathyroid Hormone–Related Peptide in Jansen's Metaphyseal Chondrodysplasia, The New England Journal of Medicine[link removed] Constitutive Activation of the Cyclic Adenosine 3',5'-Monophosphate Signaling Pathway by Parathyroid Hormone (PTH)/PTH-Related Peptide Receptors Mutated at the Two Loci for Jansen’s Metaphyseal Chondrodysplasia, Molecular Endocrinology Archived 2008-08-29 at the Wayback Machine

External links

Illustrations

Worked examples

Example 1 — a first encounter with Jansen's metaphyseal chondrodysplasia

Start with the simplest possible case. Write down what Jansen's metaphyseal chondrodysplasia claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Jansen's metaphyseal chondrodysplasia before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Jansen's metaphyseal chondrodysplasia ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Jansen's metaphyseal chondrodysplasia

In research: Jansen's metaphyseal chondrodysplasia appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Jansen's metaphyseal chondrodysplasia in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Jansen's metaphyseal chondrodysplasia is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cell surface receptor deficiencies, Growth disorders, Rare syndromes, so understanding it makes those chapters shorter.
In everyday life: Look for Jansen's metaphyseal chondrodysplasia outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Jansen's metaphyseal chondrodysplasia in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Jansen's metaphyseal chondrodysplasia means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Jansen's metaphyseal chondrodysplasia out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Jansen's metaphyseal chondrodysplasia in simple terms?

Why does Jansen's metaphyseal chondrodysplasia matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Jansen's metaphyseal chondrodysplasia?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Jansen's metaphyseal chondrodysplasia.