Vitamin D Resistant Rickets Flashcards
Inheritance
X-linked dominant disorder
Another name
Familial hypophosphtaemic rickets
Name of X-linked dominant disorders
FAIR
F = Familial Hypophosphataemic Rickets
A = Alport’s syndrome
I = Incontinentia pigmenti
R = Rett syndrome
Pathophysiology
Normally, Vitamin D increases phosphate reabsorption in the renal tubules
In vitamin D resistant rickets >>
- Imapaired phosphate reabsorption from the renal tubules >>> hypophosphatemia (low PO4 in blood)
Most common presentation
Failure to thrive in infancy
(= means failure to grow or gain weight in infancy)
Biochemical findings
Normal serum calcium
Low phosphate
High alkaline phosphatase
(Ca: normal; PO4: low, ALP: high)
X-ray changes in vitamin D resistant rickets
Epiphyses: widened +
Metaphyses: Cupped
Diagnostic/Confirmatory test/IOC
(Diagnosis is made by-?)
Urinary phosphate level: High
What are the phosphate levels in blood and urine in vitamin-D resistant rickets & why?
Low phosphate in blood & High phosphate in urine
(Due to reduced PO4 absorption in renal tubule & increased PO4 excretion)
Management
- High dose vitamin D supplements ( > increases PO4, needs high dose as resistant)
- Oral phosphate supplements
Why PTH hormone is NOT used in vitamin D resistant rickets?
Vitamin D resistant rickets has low PO4 level
PTH hormone therapy will further reduce the level
Biochemical Findings:
hypophosphataemic rickets (vitamin D resistant)
VS
Other rickets (nutritional deficiency rickets, type-I & II vitamin-D dependant rickets)
All of them >> Low phosphate, High ALP
But
Hypophosphataemic rickets: Normal calcium
Other rickets: Low calcium
Biochemical findings of Vitamin-D associated disorders:
Vitamin D resistant rickets-?
Rickets (All other types)-?
Osteomalacia-?
Vitamin D resistant rickets: Ca: Normal; PO4: Low; ALP: High
Rickets (All other types): Ca: Low; PO4: Low; ALP: high
Osteomalacia: Ca: Low; PO4: Low; ALP: high
