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Abstract: TH-PO162

Unraveling the Genotype to Phenotype Correlation: A Child with PH1 and a Novel Mutation Responsive to Pyridoxine Therapy

Session Information

Category: Trainee Case Report

  • 1700 Pediatric Nephrology

Authors

  • Prashad cortez, Ana Lucia, Inova Fairfax Hospital, Falls Church, Virginia, United States
  • Amin, Rasheda, Pediatric Specialists of Virginia, Fairfax, Virginia, United States
Introduction

Primary hyperoxaluria type 1 (MIM 259900) is a rare genetic disease with an estimated prevalence of 1-3 cases per 1 million population worldwide. Primary hyperoxaluria type 1 (PH1) is an autosomal recessive disorder, caused by a mutation in the AGXT gene, and characterized by an accumulation of calcium oxalate in various body tissues, particularly the kidney. Disease expression is variable, ranging from nephrocalcinosis during infancy to recurrent or infrequent nephrolithiasis in childhood or adulthood and renal failure in 20-50% of patients. Over 175 mutations have been identified to date. About 10 to 30% of patients with PH1, particularly those with p.Gly170Arg or p.Phe152lle mutations, respond to pyridoxine therapy with a significant reduction of urinary oxalate excretion. We present a patient with PH1, found to have a previously undescribed mutation in the AGXT gene, who showed excellent response to pyridoxine therapy.

Case Description

AS, now a nine year old male, born in Afghanistan to consanguineous parents, initially presented with a history of flank pain, failure to thrive and bilateral nephrolithiasis at the age of five years. He underwent several rounds of extracorporeal shock wave lithotripsy (ESWL) for significant stone burden. Upon establishing care with nephrology in the U.S., his workup revealed hypocitraturia, elevated 24 hour oxalate level at 127mg/day (normal range 20-40) and a urine glycolate level of 249 mg/gram of creatinine (normal range <75), raising concern for PH. He was empirically started on vitamin B6, potassium citrate and advised to increase hydration. Genetic testing confirmed PH1 with a homozygous mutation in AGXT (c.352C>T; p.Arg118Cys), reported as a variant of uncertain significance. Follow up urine testing at 3 and 7 months showed a reduction in oxalate levels by 35% and 58%, respectively. He remains asymptomatic, has normal GFR, with no evidence of systemic oxalosis and stable right sided nephrolithiasis since last ESWL in 2017.

Discussion

We conclude that in this patient with classic PH1 phenotype, the finding of a homozygous variant in AGXT is not only pathogenic, but also responsive to pyridoxine therapy. We hope this case will add to the knowledge base of PH1 and help guide management in patients with a similar genotype. Pyridoxine therapy has been life changing for AS and his family.