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Rickets and vitamin D deficiency in children
Rickets is defective mineralisation of the growth plates; the common form is nutritional vitamin D deficiency, with low-normal calcium, low phosphate, high ALP and PTH and a low 25(OH)D — and it is prevented by giving 400 IU of vitamin D a day to every infant in the first year.
Why it matters in the exam
The classic story is an exclusively breastfed toddler with dark skin or covering clothes who received no vitamin D supplement and presents with bowed legs, widened wrists, a rachitic "rosary" and delayed closure of the fontanelle or delayed teething. A young infant may instead present with a hypocalcaemic seizure. The question asks you to recognise the laboratory pattern and choose treatment.
The exam likes to compare types of rickets by the laboratory. In X-linked hypophosphataemic rickets (PHEX, high FGF23) phosphate is very low, calcium is normal, PTH is near-normal and 25(OH)D is normal, with urinary phosphate wasting; treatment is burosumab or phosphate with calcitriol, not plain vitamin D. In vitamin D-dependent rickets type 1, 1-alpha-hydroxylase is missing so 1,25(OH)2D is low; in type 2 there is receptor resistance, a high 1,25(OH)2D and sometimes alopecia.
Per the 2016 consensus, 25(OH)D below 12 ng/mL (30 nmol/L) is deficiency. Treatment of nutritional rickets is vitamin D 2000 IU a day for at least 12 weeks (or a single high dose), always together with calcium 500 mg a day, followed by a maintenance dose. A wrist or knee X-ray shows metaphyseal widening, cupping and fraying. A low ALP with a rickets picture points to hypophosphatasia — a trap.
Key points
- Nutritional rickets: low phosphate, high PTH and ALP, low 25(OH)D.
- Deficiency: 25(OH)D below 12 ng/mL (30 nmol/L).
- Treatment: vitamin D 2000 IU a day for 12 weeks + calcium 500 mg a day.
- X-linked hypophosphataemic: high FGF23, near-normal PTH; burosumab.
- Prevention: 400 IU of vitamin D a day in the first year.
Summary table
| Type | Calcium and phosphate | PTH, ALP and vitamin D | Treatment |
|---|---|---|---|
| Nutritional (vitamin D deficiency) | Low-normal calcium, low phosphate | High PTH, high ALP, low 25(OH)D | Vitamin D 2000 IU a day for 12 weeks + calcium 500 mg a day |
| Nutritional calcium deficiency | Low calcium, low phosphate | High PTH, high ALP, normal 25(OH)D | Calcium supplements |
| X-linked hypophosphataemic | Normal calcium, very low phosphate, urinary phosphate wasting | Near-normal PTH, high ALP, high FGF23 | Burosumab, or phosphate and calcitriol |
| Vitamin D-dependent type 1 | Low calcium, low phosphate | High PTH, low 1,25(OH)2D | Calcitriol |
| Vitamin D-dependent type 2 | Low calcium, low phosphate | High PTH, high 1,25(OH)2D, sometimes alopecia | High-dose calcitriol and calcium |
In the full version for subscribers
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Sources
- Global Consensus Recommendations on Prevention and Management of Nutritional Rickets, 2016 — Vitamin D status thresholds, treatment and prevention
- Israeli Ministry of Health, infant nutrition recommendations (current) — Vitamin D supplementation in the first year
- Nelson Textbook of Pediatrics, 22nd edition (2024) — Rickets and Hypervitaminosis D
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.