This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disorder of Metabolism & Connective Tissue, Subject name: Medicine
Jansen disease is? 
Select and explain. 
A. Defect of PTH receptor, B. Defect of GHRH receptor, C. Defect of ADH receptor, D. Defect of GH receptor
A: Defect of PTH receptor
Answer: A: Defect of PTH receptor 
Explanation: Ans. is 'a' i.e.. Defect of PTH receptor o Jansen syndrome occurs due to activating mutations in the PTH/PTHrP receptor (PTHIR).o Rare autosomal dominant syndrome.o The disorder leads to short-limbed dwarfism due to abnormal regulation of chondrocyte maturation in the growth plates of the bone that are formed through an endochondral process.o In adult life, there are numerous abnormalities in bone, includingy Multiple cystic resorptive areas resembling those seen in severe hyperparathyroidismy Hypercalcemia and hypophosphatemiay Undetectable or low PTH levels are typically seen.