A 3-year-old child from rural Bihar presents with bowing of legs, delayed fontanelle closure, and frontal bossing. Serum calcium is 7.2 mg/dL, phosphate 3.5 mg/dL, and alkaline phosphatase is markedly elevated. What is the most common cause of rickets in this clinical scenario?

## Most Common Cause of Rickets in India **Key Point:** Nutritional deficiency rickets due to inadequate vitamin D intake and/or sunlight exposure remains the most common cause of rickets worldwide, particularly in developing countries like India. ### Epidemiology - Accounts for >90% of rickets cases in endemic regions - Highest prevalence in children aged 6 months to 5 years - More common in populations with limited sun exposure, dietary restrictions, or malabsorption - Rural areas with poor nutrition show higher incidence ### Clinical Presentation in This Case The child presents with classic features of nutritional rickets: - **Skeletal deformities:** Bowing of legs (genu varum or valgum) - **Cranial signs:** Frontal bossing, delayed fontanelle closure - **Biochemical pattern:** Low calcium, low-normal phosphate, elevated alkaline phosphatase - **Age group:** 3 years is typical for rickets manifestation ### Biochemical Distinction | Feature | Nutritional Rickets | X-linked Hypophosphatemia | Renal Rickets | VDD Rickets Type 1 | |---------|-------------------|------------------------|---------------|-------------------| | **Serum PO₄** | Low | Very low | Normal/High | Low | | **Serum Ca** | Low | Normal | Low | Low | | **ALP** | ↑↑↑ | ↑↑ | ↑↑ | ↑↑ | | **25-OH D** | **Very low** | Normal | Normal | Normal | | **1,25-OH₂ D** | Low | High | Low | Very high | | **PTH** | Elevated | Normal/Low | Elevated | Low | | **Prevalence** | **Most common** | Rare genetic | Secondary to CKD | Rare genetic | **High-Yield:** The serum 25-hydroxyvitamin D level (not measured in this stem but implied by the clinical context) would be markedly low in nutritional rickets, distinguishing it from genetic forms where 25-OH D is normal. ### Why Nutritional Rickets is Most Common 1. **Dietary insufficiency:** Limited milk intake, vegetarian diets low in fortified foods 2. **Sunlight deprivation:** Indoor lifestyle, cultural clothing practices, high latitude/pollution 3. **Malabsorption:** Concurrent GI disorders (celiac disease, cystic fibrosis) 4. **Socioeconomic factors:** Poverty, food insecurity in rural India **Clinical Pearl:** In Indian children, always suspect nutritional rickets first. The combination of low calcium, low-normal phosphate, and elevated ALP in a rural child with skeletal deformities is pathognomonic. **Mnemonic — RICKETS causes (in order of frequency):** **N**utritional (most common) → **R**enal → **H**ypophosphatemic → **V**itamin D-dependent → **H**ypoparathyroidism