Calcium and Phosphate Metabolism

Question 1

What is a genetic cause of osteomalacia?

Answer 1

Mutations leading to errors in vit D metabolism (rare)

Question 2

What is a genetic cause of osteomalacia?

Answer 2

Mutations leading to errors in vit D metabolism (rare)

Question 3

What is a genetic cause of secondary hyperparathyroidism?

Answer 3

• Alpha hydroxylase mutation and/or vit D receptor mutation = low calcium and active calcitriol will be low = high PTH = secondary hyperparathyroidism

Question 4

What is FGF-23?

What are disorders linked to FGF-23?

Answer 4

FGF-23: a hormone secreted by osteocytes
• Phosphate balance: increases renal excretion
• Disorders:
• Oncogenic osteomalacia (tumour secreting FGF-23)
• X-linked hypophophataemic rickets
• Autosomal dominant hypopho-phataemic rickets (gain of function mutation)