Hereditary Hypophosphatemic Rickets with Hypercalciuria-Importance of Further Evaluation when Clinical Suspicion is Strong

Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is a rare genetic condition with autosomal recessive inheritance and a prevalence of 1 in 250000. It is due to mutation of the SLC4A3 gene. Correct diagnosis of this condition is important as treatment with active vitamin D metabolites is contraindicated. Evolution of the disease despite initial completely normal biochemistry has been observed, potentially creating diagnostic confusion. The first child presented at the age of 5.5 years with features of rickets. He had an abnormal bone profile with normal vitamin D levels. Urinary phosphate studies were compatible with HHRH. He was treated with phosphate supplementation and potassium citrate. He has well responded well to treatment. The second child initially presented at 1.5 years of age with leg bowing and a family history of hypercalciuria. All investigation findings, including urinary phosphate studies, were within normal limits. At the age of 2.5 years, he again presented with worsening of bowing. Biochemical and urinary investigations were repeated and laboratory findings were now compatible with HHRH. These cases highlight the importance of repeated investigations despite initial normal parameters, if the initial clinical suspicion is strong. Clinical- and investigation-based diagnosis of this rare genetic disease, HHRH, is feasible in resource limited setting.