Endocrine Abstracts

JOINT2233

Introduction: Renal tubular acidosis is characterized by persistent normal anion gap metabolic acidosis. It may be hereditary(primary) or secondary to disease conditions or drug use. Hereditary distal renal tubular acidosis (dRTA) is a rare genetic disease caused by mutations in either SLC4A1, ATP6VOA4 or ATP6V1B1 genes that encode the chloride-bicarbonate exchanger (AE1) or subunits of the H-ATPase pump. Affected individuals typically present with rickets, growth failure due to metabolic acidosis. This disease condition remains undiagnosed in most cases. This report is to create awareness about dRTA as a possible cause of rickets and short stature and to avoid the confusion with hypophosphatemic rickets.

Case Summary: 17-year female adolescent with bony deformity first noticed in infancy presented to an orthopaedic hospital where she commenced on oral calcium and vitamin D in treatment for rickets. In view of recurrent history of fractures following minimal impacts despite use of calcium and vitamin D, she was referred to paediatric endocrinology clinic for possible vitamin D resistant rickets. There was no history suggesting autoimmune diseases or chronic drug use. She attained menarche at 15years but menstrual cycles stopped. Her weight was 19kg; length was 106cm -(minus)8. 5, and body mass index was 16. 9kg/m² -(minus)1. 71. Upper to lower segment ratio was 0. 95:1. Musculoskeletal system examination revealed telephone shaped deformity of the long bones and fork deformity of the wrist. Serum calcium was normal; 2. 41 mmol/l (2. 10 -2. 55), serum phosphate was 0. 51 mmol/l ↓ (0. 97 -1. 68), 25 hydroxyvitamin D was 56. 5 nmol/l (normal), Alkaline phosphatase was elevated at 692µ/l (79-370), parathyroid hormone was remarkably low < 1. 2 pg/ml (18. 50 – 88. 0). Serum electrolytes showed acidosis and hypokalemia with a normal anion gap. Urinalysis showed specific gravity of 1. 050, pH:8, low urine calcium (0. 59 mmol/l) phosphate (4. 8 mmol/l). On evaluation for vitamin D resistant rickets, FGF23 was normal. Whole genome sequencing returned positive for de novo heterozygous pathogenic variants in SLC4A1 of distal renal tubular acidosis with autosomal dominant mode of inheritance. There was an improvement with acidosis and hypokalemia on commencement of baking powder, phosphate and potassium therapy. She is also on calcitriol and calcium.

Conclusion: Rickets and growth failure are established presentations of dRTA. Serum electrolytes and urinalysis check in evaluation of a child with features of hypohosphatemic rickets are necessary to rule out dRTA.

Keywords: Distal renal tubular acidosis, children, Nigeria, Fractures, Short stature.