Case Presentation: A previously healthy 7-month-old male infant was admitted after having a new onset 10-minute seizure. He was exclusively breastfed until 2 weeks prior to admission. His mother reported decreased oral intake since switching to formula and introducing solid foods. The infant had not been taking any vitamins.Physical exam: The patient was afebrile, alert, and tracking appropriately. There were no cardiac murmurs or craniofacial abnormalities. His neck was supple, and he had full range of motion throughout his extremities without rigidity. Neurological exam was unremarkable. Chvostek’s and Trousseau’s signs were negative.Labs and studies: Calcium levels were severely low and phosphorus was elevated (Table 1). Urine calcium was normal. Parathyroid hormone (PTH) was normal and vitamin D was severely low. Iron and thyroid studies were unrevealing. X-rays of the knees and wrists showed no osseous abnormalities or evidence of rickets. Subsequent course: The patient’s laboratory tests showed hypoparathyroidism. He was evaluated with a karyotype which revealed an interstitial deletion of chromosome 10 involving the GATA3 gene, a transcription factor involved in the embryonic development of the parathyroid glands.1 Based on this result, he was diagnosed with HDR disease (hypoparathyroidism, sensorineural deafness and renal disease). His hypocalcemia was further exacerbated by vitamin D deficiency due to lack of supplementation during breastfeeding. He was started on ergocalciferol, calcium carbonate, and calcitriol with resultant normalization of his calcium and vitamin D levels by 6-week follow-up.

Discussion: Pediatric hospitalists should be familiar with the causes and workup needed for evaluation of hypocalcemia in infancy, and recognize lab abnormalities that raise concern for primary hypoparathyroidism. The most common causes of chronic hypocalcemia can be divided into two major groups: disorders involving PTH and those related to vitamin D. Thus, lab evaluation of such patients should include these levels, along with serum calcium, phosphorous, magnesium, and hepatic function panel.2 Our patient’s persistent hypocalcemia with an inappropriately normal PTH level and hyperphosphatemia is what led to the diagnosis of hypoparathyroidism, despite his vitamin D deficiency.

Conclusions: Hypoparathyroidism can be caused by primary or acquired conditions. Although less common, genetic causes of hypoparathyroidism should be considered in infants once acquired conditions have been ruled out. They can be identified by cytogenetics studies (i.e., microarray and karyotype). If positive, as in our case, the patient should be referred for appropriate genetic counseling as the disorder may be associated with a complex syndrome that can result in comorbidities, or have implications on future parental family planning.

IMAGE 1: Table 1: Patient Laboratory Results