Study in Healthy Subjects, Patients With Urea Cycle Disorders (UCD) and Carriers of UCD Mutations to Evaluate Urea Cycle Function

Inclusion Criteria: All study groups: • Written informed consent given by subjects or his/her parents/legal guardians who are able to understand and follow instructions related to the study Group 1 Healthy Volunteers: * Age: 18 - 65 years * Healthy subjects * No clinical or laboratory parameter outside normal ranges at screening and judged as clinically relevant by the investigator Group 2 Symptomatic UCD patients with genetically confirmed CPSD, OTCD, ASSD, or ASLD: Age: 0 - 65 years * Symptomatic subjects with genetically confirmed Carbamylphosphate synthetase I Deficiency \[CPSD\], Ornithine Transcarbamylase Deficiency \[OTCD\], Argininosuccinate Synthetase Deficiency \[Citrullinaemia type I\], Argininosuccinate Lyase Deficiency \[ASLD\] * at least 1 metabolic decompensation with clinical signs of hyperammonemia in medical history or genetically confirmed and prospectively treated siblings of symptomatic patients, even without clinical symptoms * Confirmed diagnosis and medical history available (in particular number and severity of metabolic crises) Group 3 Asymptomatic carriers of UCD mutations: * Age: 0 - 65 years * Asymptomatic carriers of mutations for Carbamylphosphate synthetase I Deficiency \[CPSD\], Ornithine Transcarbamylase Deficiency \[OTCD\], Argininosuccinate Synthetase Deficiency \[Citrullinaemia type 1\], Argininosuccinate Lyase Deficiency \[ASLD\] no dietary protein restriction, no intake of ammonia scavenging drugs, no known metabolic decompensation with clinical signs of hyperammonemia Group 4: * Infants between 8 - 10 kg body weight Symptomatic subjects with genetically confirmed Carbamylphosphate synthetase I Deficiency \[CPSD\] Ornithine Transcarbamylase Deficiency \[OTCD\] Argininosuccinate Synthetase Deficiency \[Citrullinaemia type I\] Argininosuccinate Lyase Deficiency \[ASLD\] at least 1 metabolic decompensation with clinical signs of hyperammonemia in medical history or genetically confirmed and prospectively treated siblings of symptomatic patients, even without clinical symptoms * Confirmed diagnosis and medical history available (in particular number and severity of metabolic crises Exclusion Criteria: * Acute illness, including vomiting, fever or other sign of infection * Participation in other invasive clinical trials within 30 days prior to inclusion * Liver or renal disease * Acute seizures * Coma * Bleeding disorder * Blood ammonia \> 100 µmol/l for patients with a urea cycle disorder and blood ammonia \> normal for healthy probands and asymptomatic carriers * Metabolic acidosis * Pregnancy or lactation * Body weight \< 8kg * Chronic somatic or psychiatric disease not related to UCD