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Question: A 9-year-old girl is brought to a new pediatrician by her mother over concerns regarding her weight. She has a history of developmental delay, and her mother mentions that she is noticeably shorter than her peers. She is noted to have a round face and bilaterally shortened fourth metacarpals on examination. She is in the 96th percentile for weight and below the 3rd percentile for height for her age. Laboratory testing reveals hypocalcemia.

Which additional laboratory findings are associated with this patient’s most likely diagnosis?

A. Low parathyroid hormone and phosphate levels

B. Normal parathyroid hormone and elevated phosphate levels

C. Normal parathyroid hormone and low phosphate levels

D. Elevated parathyroid hormone and phosphate levels

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Details: This patient’s findings are suggestive of Type 1a pseudohypoparathyroidism (PHP), an autosomal dominant disease that is characterized by renal resistance to parathyroid hormone (PTH). Patients with Type 1a PHP have hypocalcemia, hyperphosphatemia, and elevated PTH concentrations. The condition is associated with Albright hereditary osteodystrophy (AHO), a constellation of clinical features including round facies, short stature, obesity, developmental delay, and shortened fourth metacarpal bones. While features of AHO are also present in patients with pseudo-pseudohypoparathyroidism, those patients will have normal levels of calcium, phosphate, and PTH.

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