Related Subjects:
|Vitamin D Replacement
|Osteomalacia-Rickets-Vitamin D
|Vitamin D resistant rickets
|Vitamin D (25 OH D) Testing
|X linked Hypophosphataemic rickets
|Osteoporosis
In Hypophosphatemic Rickets, there is renal phosphate wasting and hypophosphatemia. Patients typically do not respond to standard Vitamin D therapy.
About
- Hypophosphatemic Rickets: Also known as Vitamin D-Resistant Rickets, a condition characterized by defective renal phosphate reabsorption leading to bone weakening and growth abnormalities.
- X-linked dominant inheritance pattern, though autosomal recessive and sporadic forms also exist.
- It is most commonly diagnosed in children with rickets that fail to respond to standard Vitamin D therapy.
Renal Tubular (RT) Forms
- Type I: Characterized by low renal 1-alpha-hydroxylase activity, resulting in insufficient activation of Vitamin D.
- Type II: Defined by end-organ resistance to 1,25-dihydroxyvitamin D3(the active form of Vitamin D).
- Both forms are treated with large doses of calcitriol (1,25-dihydroxy-vitamin D).
Aetiology
- Decreased proximal renal tubular reabsorption of phosphate, leading to excessive phosphate loss in urine (phosphate wasting).
- This results in hypophosphatemia, which impairs bone mineralization and leads to rickets.
- Decreased intestinal absorption of calcium and phosphate due to defective activation of Vitamin D.
Clinical Features
- Usually diagnosed in infants or young children with signs of rickets.
- Short stature: Growth failure and bone deformities, particularly affecting the femur and tibia (bowed legs).
- Delayed dentition: Abnormally delayed or incomplete development of teeth, often associated with dental abscesses.
- May present with other features such as:
- Deafness
- Chiari malformation: Structural defects in the cerebellum.
- Calcification of soft tissues: Including tendons, ligaments, and joint capsules.
- Craniosynostosis: Premature fusion of skull bones.
- Renal stones: Due to abnormal calcium metabolism.
Investigations
- ↓ Serum phosphate (PO4) levels.
- ↑ Alkaline phosphatase (ALP) due to increased bone turnover.
- ↑ Urinary phosphate excretion, reflecting renal phosphate wasting.
- ↓ Serum calcium (in some cases).
- ↑ Parathyroid hormone (PTH) due to secondary hyperparathyroidism.
- Normal 25-hydroxyvitamin D levels (but the active form is deficient).
- Renal ultrasound (USS) may reveal kidney stones or nephrocalcinosis.
Management
- Large doses of 1,25-dihydroxy-vitamin D (calcitriol) to compensate for defective Vitamin D metabolism.
- Oral phosphate supplements to replace the phosphate lost in urine.
- Growth hormone therapy may be considered to promote growth in affected children.
- Amiloride or thiazide diuretics may be used to enhance calcium reabsorption, reducing the risk of nephrocalcinosis (calcium deposition in the kidneys).
References