USMLE (United States Medical Licensing Examination) Step 1 Practice Exam

Which conditions present physical exam features of Albright hereditary osteodystrophy without end-organ PTH resistance?

1. Pseudopseudohypoparathyroidism

2. MEN 1

3. MEN 2a

4. MEN 2b

The correct answer is: Pseudopseudohypoparathyroidism

Albright hereditary osteodystrophy is characterized by a distinct physical exam presentation, including short stature, round face, and subcutaneous ossifications, which are features of pseudohypoparathyroidism due to Gs alpha subunit mutations that affect hormone signaling. However, individuals with pseudopseudohypoparathyroidism exhibit the same physical traits as Albright hereditary osteodystrophy but do not experience the end-organ PTH resistance that defines pseudohypoparathyroidism. In pseudopseudohypoparathyroidism, the genetic mutation affects the same gene associated with Albright hereditary osteodystrophy, but the critical difference is that these individuals have normal parathyroid hormone (PTH) levels and normal PTH responses due to the absence of resistance at the level of the kidneys and bones. Thus, they present with the characteristic physical features but without the biochemical abnormalities associated with PTH resistance. Other conditions listed, such as MEN 1 and MEN 2a/2b, primarily involve endocrine tumors and different hormonal pathways and do not exhibit the specific physical manifestations associated with Albright hereditary osteodystrophy, which is why they do not fit the criteria presented in this question.