Background: Congenital lactase deficiency (CLD) occurs as a result of loss of function of intestinal lactase-phlorizin hydrolase (LPH) encoded by LCT gene. Patients usually present with osmotic diarrhea in the first few days of life. Although the exact mechanism is not known, hypercalcemia is a common feature of CLD; with calcium levels up to 14 mg/dl and nephrocalcinosis have been reported. However, CLD is frequently overlooked in the differential diagnosis of hypercalcemia. Here, we present a patient admitted for dehydration and hypercalcemia in whom CLD was considered due to diarrhea and failure to thrive.
Case report: A two month-old girl presented with vomiting and failure to thrive. She was born at term with a birth weight of 3030 gr to first cousin parents. She had severe dehydration and her height, weight and head circumference were 55 cm (-1.25 SDS), 3.4 kg (-2.83 SDS) and 36 cm (-2.69 SDS), respectively. Hypercalcemia, hyponatremia and metabolic acidosis were detected on laboratory evaluation (Ca:17.3 mg/dl, Na:127 mEq/L, pH:7.22, HCO3:10.6, İ.Ca:9.1 mg/dl). Additionally, the patient had hypercalciuria (Urine ca/cr:1.05 mg/mg), and medullary nephrocalcinosis on renal ultrasound. Etiological evaluation for hypercalcemia was unrevealing except low 1.25(OH)2D level (22 pg/ml). She was started on intravenous fluid and 1 mg/kg methylprednisolone was given once. Further history revealed that she had watery-foamy diarrhea starting shortly after birth despite being fed exclusively with breast milk. A malabsorbtion was considered and she was placed on lactose-free (LF) formula. Serum calcium, decreased to 13.6 mg/dl on the second day after hydration and methyl prednisolone and returned to normal within a month of initiating LF formula. No further hypercalcemia was detected on follow-up. Her diarrhea and vomiting also ceased and the patient started to thrive well. On her last examination, when she was 7.5-year-old, her height and weight were 116.6 cm (-1.3 SDS) and 27 kg (0.71 SDS), respectively with normal biochemistry. Molecular genetic evaluation revealed absence of mutations related to the hypercalcemia but identified bi-allelic c.1364T>C (p.Ile455Thr) mutation in the LCT gene.
Conclusion: Cause-specific treatment in hypercalcemia prevent unnecessary nonspecific treatments (Bisphosphonates, calcitonin etc) as LF diet provided and maintained normocalcemia in our patient. CLD should be kept in mind in the differential diagnosis of hypercalcemia and history of diarrhea should be carefully sought in these patients.