This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Parathyroids, Subject name: Pathology
A 15-year-old boy with Albright hereditary osteodystrophy (AHO) is rushed to emergency room with severe muscle cramps and convulsions. The child has a history of mental retardation. Laboratory studies reveal hypocalcemia and elevated blood levels of PTH. Which of the following distinguishes this patient's endocrinopathy from hypoparathyroidism seen in DiGeorge syndrome? 
Select and explain. 
A. Abnormalities in cardiac conduction and contractility, B. Accelerated degradation of PTH, C. Decreased neuromuscular excitability, D. End-organ unresponsiveness to PTH
D: End-organ unresponsiveness to PTH
Answer: D: End-organ unresponsiveness to PTH 
Explanation: - Given clinical features suggests the diagnosis of pseudo-hypoparathyroidism. Pseudo-hypoparathyroidism Group of hereditary conditions a/w maternal imprinting in which hypocalcemia is caused by target organ insensitivity to parathyroid hormone. High PTH level is seen by feedback. - Whereas in DiGeorge syndrome, hypocalcemia is d/t decreased PTH levels as a result of absent parathyroid glands - Pseudo-hypoparathyroidism patient's demonstrate characteristic phenotype (Albright Hereditary Osteodystrophy) : Sho stature Obesity Mental retardation Subcutaneous calcification Congenital anomalies of bone - Small 4th & 5th metacarpals - Knuckle-knuckle-Dimple-Dimple sign/ Archibald sign.