RESUMEN
INTRODUCTION: Citrullinemia type I (CTLN1) is a rare autosomal recessive metabolic disorder. Symptoms typically include vomiting, lethargy, seizures and coma. In neonatal presentation, death occurs in days if untreated. Survivors may evolve with neurocognitive dysfunction. RESULTS/CASE REPORT: Two 10 years old, non-identical, twin sisters (S1; S2) with CTLN1 were born after a 36W gestation: S1 by eutocic delivery and S2 by cesarean section with nuchal cord (Apgar score 5/10). On day four, S2 presented hyperammonemia with coma. S1 had no complications. Diagnosis followed that of S2. Neurocognitive development was monitored at 3 months - 4 years of age with Griffiths Scales: global development quotient kept within the average, but S2 had a deficit in language and eye and hand coordination. At 5 years, the neurocognitive abilities were evaluated using Wechsler Preschool and Primary Scale of Intelligence - Revised (WPPSI-R). S2 revealed difficulties in verbal area (vocabulary, comprehension and memorizing sentences), with a lower average verbal intelligence quotient (IQ). S1 had high average IQ. Due to learning difficulties, S2 was reassessment at 8 years old with Wechsler Intelligence Scale for Children - Third edition (WISC-III): full-scale IQ -"extremely low". CONCLUSION: These non-identical twin sisters share the same citrullinemia type 1 causing variants in the ASS1 gene. Nevertheless, their clinical presentation and neurocognitive evolution are diverse. Other factors, like the different genetic background and perinatal issues such as the type of delivery and its circumstances and the neonatal coma episode of S2 may explain the dissimilar evolution. Maximum ammonium levels (and its duration) are critical for the patients' neurodevelopment: 131 in S1 and 546 umol/l in S2.
