In this short-term study a method for the evaluation of the metabolic competency of the urea cycle in vivo will be assessed. In order to monitor the efficacy of new treatment options for patients with urea cycle disorders and to monitor the severity of the disease, a reliable and safe quantitative method for the measurement of the urea cycle flux is required.

Urea synthesis will be evaluated by administering sodium [1-13C]-acetate and measuring subsequent incorporation of [13C] label from Na-acetate into urea in healthy volunteers and asymptomatic subjects genetically disposed to urea cycle disorders.

Inclusion Criteria:

• Group 1 + 2: Healthy subjects
• Group 3: Healthy asymptomatic subjects genetically disposed to urea cycle disorders
• All: age 18 to 50 years (adult)
• Written informed consent

Exclusion Criteria:

• Presence of acute infection
• Participation in other clinical trials within 30 days prior to inclusion
• Severe coagulopathy
• Severe systemic or chronic disease
• Pregnancy or lactation