2.1. Study design

Seventeen CTLN1 patients from 10 unrelated families were enrolled in the study. The Iranian National Society for Study on Inborn Errors of Metabolism in Tehran is an institution that accepts patients from every province of Iran. The current study included patient reports between 2008 and 2020. Diagnosis was based on clinical symptoms and laboratory confirmation, elevated plasma citrulline levels determined by mass spectrometry upon newborn screening or by high performance liquid chromatography later, hyperammonemia determined by an enzymatic spectrophotometric assay (Randox Ammonium Kit, Randox Laboratories LTD, UK), and orotic aciduria determined by thin layer chromatography (normally not detected). Standard treatment with ammonia scavengers, peritoneal dialysis, exchange transfusion (if dialysis was not available), l‐arginine, l‐carnitine, a low‐protein diet, and special urea cycle defect formulas was carried out after diagnosis. Then, age of onset, clinical presentation, plasma citrulline, glutamine and ammonia levels, clinical outcome, family history, and molecular genetic analysis were retrospectively evaluated.