Further workup revealed hypocalcemia (total calcium of 6.8 mg/dL, ionized calcium of 0.91 mmol/L), severe vitamin D deficiency (25-hydroxyvitamin D of 3.5 ng/mL), low phosphate, elevated alkaline phosphatase, and a high serum parathyroid hormone level, all indicative of nutritional rickets. The gene discussed is PTH; the disease is vitamin D deficiency.