A 7-year-old boy presents with progressive bowing of his legs and a waddling gait. He has a history of multiple dental abscesses. Laboratory studies show a normal serum calcium, low serum phosphorus, high alkaline phosphatase, and an inappropriately normal 1,25-dihydroxyvitamin D level. Which of the following is the most appropriate long-term treatment?
A 10-month-old infant is brought to the clinic for evaluation. His diet consists primarily of goat’s milk and homemade vegetable purées. The mother reports he has been increasingly irritable and has had several generalized seizures over the last week. Laboratory studies show a microcytic anemia. An electroencephalogram (EEG) is abnormal. Which vitamin deficiency should be suspected?
A 5-month-old infant presents with failure to thrive, recurrent diarrhea, and oral ulcers. Laboratory evaluation reveals megaloblastic anemia. The infant is found to have a severe combined immunodeficiency. Serum folate levels are low. Cerebrospinal fluid (CSF) folate is also profoundly low. What is the most likely diagnosis?
A 7-month-old dark-skinned infant, living in a northern city during winter, is brought to the emergency department with seizures. The infant is exclusively breastfed, and the mother does not take prenatal vitamins. Laboratory results show hypocalcemia, hypophosphatemia, and markedly elevated alkaline phosphatase and parathyroid hormone levels. What is the most likely diagnosis?
An 18-month-old child presents with new-onset ataxia and ophthalmoplegia. The parents report a several-month history of dry, scaly skin patches and poor night vision. Laboratory results are notable for a serum vitamin E to total lipid ratio of 0.5 mg/g. The child has no history of steatorrhea or liver disease. What is the most likely diagnosis?
A 1-year-old boy is brought to the clinic for a well-child visit. His parents are concerned about his diet, which consists almost entirely of polished rice and a few vegetables. On examination, the physician notes hoarseness of his cry, tachycardia, and a palpable liver. Which condition should be at the top of the differential?
A 7-year-old female presents with rickets. Laboratory evaluation demonstrates hypophosphatemia with renal phosphate wasting, an elevated 1,25-dihydroxyvitamin D level, and hypercalciuria. Serum parathyroid hormone level is suppressed. Pathogenic variants in which gene would most likely explain these findings?
A 2-month-old premature infant (born at 28 weeks gestation) who is receiving parenteral nutrition develops a hemolytic anemia and thrombocytosis. Physical exam is also notable for edema. Which vitamin deficiency is the most likely cause?
A 6-month-old infant presents with developmental delay, irritability, and hyperpigmentation of his knuckles and the soles of his feet. Lab work shows megaloblastic anemia. His mother is a healthy lacto-vegetarian. A trial of oral high-dose vitamin B12 shows no improvement in biochemical markers. Which of the following is the most likely diagnosis?
A 15-year-old female with a history of anorexia nervosa is admitted for medical stabilization. Her Body Mass Index is 15 kg/m². On day 3 of refeeding, she develops shortness of breath, tachycardia, and a new cardiac arrhythmia. Laboratory workup is significant for severe hypophosphatemia. The fluid and electrolyte shifts seen in this patient are primarily driven by the release of which hormone?
