ESPE Abstracts

Background: Hypercalciuria, short stature and low bone mineral density are features of distal renal tubular acidosis (dRTA) and osteogenesis imperfecta (OI). If untreated, the presence of dRTA in patients with OI may worsen the prognosis and lead to poorer height outcomes. We describe two unrelated children with an unusual association between OI and dRTA.

Cases: Patient 1 is a 7-year-old female diagnosed prenatally with a COL1A2 mutation and postnatally with type IV OI who presented at 20 months of age with metabolic acidosis and inappropriately alkaline urine, in the setting of family history for dRTA. She had a low urine PCO2 (maximum 28 mmHg; normal >60–70 mmHg) and low urine-blood PCO2 after acetazolamide test and has since been on potassium citrate treatment with correction of the acidosis. Patient 2 is a 13-year-old male diagnosed with type I OI at 16 months of age (COL1A1 mutation) who had an abnormal acetazolamide test a few months later (maximum urine PCO2: 29 mmHg; normal >60–70 mmHg). He received therapy with potassium citrate until 10 years of age, when it was successfully discontinued. Patients 1 and 2 both had intermittent hypercalciuria, but distinct OI severity: patient 1 is growing below the 3rd percentile and has frequent fractures requiring bisphosphonate therapy, while patient 2, who never received bisphosphonates, is growing at the 50th percentile with no recurrent fractures.

Conclusion: Case reports in the literature describe dRTA initially misdiagnosed as OI, but this is, to our knowledge, the first description of coexistence of the two conditions. The etiology of hypercalciuria in OI has not been fully elucidated. We hypothesize that in some patients it may be secondary to dRTA, and alkali therapy could prevent nephrocalcinosis and nephrolithiasis along with improving height attainment and bone disease.