Carbamoyl Phosphate Synthetase Deficiency

Carbamoyl phosphate synthetase deficiency is a rare, inherited problem of the urea cycle—the body’s system for removing extra ammonia, a waste made when we break down protein. CPS1 is the first liver enzyme that starts this cycle. When CPS1 does not work well, ammonia builds up in the blood (hyperammonemia). Ammonia is toxic to the brain. High ammonia can cause sleepiness, vomiting, fast or deep breathing, confusion, seizures, coma, and brain swelling if not treated fast. MedlinePlus+2rarediseases.info.nih.gov+2

Carbamoyl phosphate synthetase I (CPS1) deficiency is a rare genetic disorder of the urea cycle—the body’s main system for clearing ammonia, a toxic waste from protein breakdown. When the CPS1 enzyme (the first step inside liver cell mitochondria) does not work well, ammonia builds up in the blood (hyperammonemia). Very high ammonia can injure the brain and cause poor feeding, vomiting, sleepiness, confusion, seizures, coma, or death if not treated quickly. CPS1 deficiency often presents in the first days of life but can also appear later during illness, fasting, or heavy protein intake. Management focuses on keeping ammonia low with diet, special medicines that bind nitrogen, prompt emergency care during “metabolic crises,” and—when needed—liver transplantation, which can correct the enzyme defect. PMC+3NCBI+3PMC+3

How the enzyme works (why ammonia rises): CPS1 sits at the very start of the urea cycle and needs a natural “on switch” called N-acetylglutamate (NAG). If CPS1 is faulty, the cycle cannot start, so ammonia cannot be converted to urea and safely excreted. Because the block is at the first step, blood citrulline tends to be low and orotic acid is usually not high (helps distinguish from OTC deficiency). NCBI+1

CPS1 deficiency is autosomal recessive. This means a child gets one non-working gene from each parent. If both copies are faulty, the enzyme is low or absent. Some people have severe disease starting in the first days of life. Others have milder disease with later episodes during illness, fasting, intense exercise, pregnancy, or other stress. MedlinePlus+2Rare Diseases Clinical Research Network+2

---

Other names

Doctors may also call this condition:

• Carbamoyl-phosphate synthetase I deficiency (CPS1 deficiency, CPS1D)

• Hyperammonemia due to CPS1 deficiency

• Urea cycle disorder—CPS1 type
  All of these terms refer to the same enzyme problem causing high ammonia. Rare Diseases Clinical Research Network+1

---

Types

1) Neonatal-onset (early-onset) CPS1 deficiency.
A full-term baby seems well at birth. In 24–72 hours, the baby becomes sleepy, feeds poorly, vomits, breathes fast, and may have seizures. Ammonia is very high. This is the most severe form and needs emergency care. Orpha+1

2) Late-onset (partial) CPS1 deficiency.
Children, teens, or adults can have sudden episodes of confusion, headache, vomiting, ataxia (shaky walking), or behavior changes—often during infections, fasting, high-protein intake, postpartum period, or after surgery. Between attacks, they may feel normal. NCBI+1

3) Severity spectrum by enzyme activity.
Some people have almost no CPS1 activity (severe), others have partial activity (milder). The amount of working enzyme, and the trigger, shape how and when symptoms appear. Rare Diseases Clinical Research Network

---

Causes

Remember: the root cause is biallelic pathogenic variants in the CPS1 gene. The items below explain direct genetic causes and common triggers that cause attacks in people who already have CPS1 deficiency.

1. Pathogenic CPS1 variants (overall) – Two harmful changes in the CPS1 gene lower enzyme activity and cause hyperammonemia. Orpha

2. Missense variants – A single amino-acid change can make the enzyme fold poorly or work slowly. Severity varies. malacards.org

3. Nonsense or frameshift variants – Create truncated enzyme, often severe, with near-absent function. malacards.org

4. Splice-site variants – Disrupt normal RNA splicing so the enzyme is incomplete or unstable. malacards.org

5. Large deletions/duplications – Remove or repeat parts of CPS1, reducing function. malacards.org

6. Compound heterozygosity – Two different CPS1 variants (one from each parent) together reduce function. Rare Diseases Clinical Research Network

7. Severe neonatal enzyme deficiency – Very low/absent activity from two severe variants → early crisis. Orpha

8. Partial enzyme deficiency – “Hypomorphic” variants leave some activity → later onset. Rare Diseases Clinical Research Network

9. High protein load – A big protein meal or rapid protein refeeding increases ammonia beyond the limited urea cycle capacity. BioMed Central

10. Fasting/catabolism – Illness or fasting breaks down body protein, releasing ammonia and triggering attacks. BioMed Central

11. Intercurrent infections – Fever and inflammation drive catabolism and raise ammonia. BioMed Central

12. Surgery or trauma – Surgical stress increases protein breakdown and nitrogen load. BioMed Central

13. Postpartum period – Hormonal and metabolic shifts can precipitate episodes in women. NCBI

14. Certain medicines (e.g., valproate) – Some drugs can worsen hyperammonemia or interfere with the urea cycle. BioMed Central

15. Gastrointestinal bleeding – Digested blood acts like a high-protein meal, adding nitrogen. BioMed Central

16. Excessive exercise or extreme dieting – Increases catabolism and nitrogen. ScienceDirect

17. Dehydration – Reduces renal clearance and worsens metabolic stress. BioMed Central

18. Low intake of essential calories – Without enough carbs/fat, the body burns protein, raising ammonia. BioMed Central

19. Delayed diagnosis and late treatment – Prolonged hyperammonemia worsens brain injury and future vulnerability. BioMed Central

20. Lack of N-acetylglutamate (NAG) stimulation – While NAGS deficiency is a different disorder, low NAG during stress can further limit CPS1 activity, aggravating hyperammonemia in CPS1D. NCBI

---

Symptoms and signs

1. Poor feeding and vomiting – The body rejects feeds when ammonia rises; this is common in newborns. rarediseases.info.nih.gov

2. Sleepiness or lethargy – Ammonia depresses brain function, causing drowsiness and low energy. MedlinePlus

3. Low body temperature (hypothermia) in infants – The brain’s temperature control fails during crises. rarediseases.info.nih.gov

4. Weak muscle tone (hypotonia) – Muscles feel floppy because the brain cannot send normal signals. rarediseases.info.nih.gov

5. Fast or deep breathing (respiratory alkalosis) – The brain responds to high ammonia by driving fast breathing; blood gases show alkalosis. MSD Manuals

6. Irritability and behavior change – Unusual crying, agitation, or withdrawal can precede severe symptoms. malacards.org

7. Confusion and disorientation – Clear sign of brain toxicity from ammonia in older children/adults. NCBI

8. Ataxia (unsteady walking) – The person may stagger or have trouble with balance. NCBI

9. Headache – May reflect brain swelling or metabolic stress. PMC

10. Seizures – Severe hyperammonemia can trigger seizures. rarediseases.info.nih.gov

11. Coma – Extremely high ammonia can shut down consciousness and is life-threatening. rarediseases.info.nih.gov

12. Poor growth or feeding aversion – Chronic protein intolerance can limit growth. Rare Diseases Clinical Research Network

13. Developmental delay – Repeated or prolonged high ammonia can injure the brain and slow development. BioMed Central

14. Learning problems or attention issues – Even with treatment, some have cognitive impacts after crises. BioMed Central

15. Psychiatric or mood symptoms – Anxiety, irritability, or behavior changes may appear in late-onset forms. PMC

---

Diagnostic testing

A) Physical exam

1. General appearance and vital signs.
   Doctors look for lethargy, poor feeding, vomiting, low temperature (in infants), and rapid breathing. These are early clinical clues of hyperammonemia. rarediseases.info.nih.gov+1

2. Neurologic exam.
   Checks alertness, reflexes, tone, and seizures. A falling level of consciousness signals rising ammonia and possible cerebral edema. MedlinePlus

3. Hydration status.
   Dry mouth, low tears, and poor skin turgor suggest dehydration, which worsens crises and must be corrected. BioMed Central

4. Liver size and tenderness.
   Although CPS1 deficiency is a liver-based enzyme disorder, the liver is usually structurally normal; exam supports ruling out other liver diseases. BioMed Central

5. Nutritional assessment.
   Weight, growth pattern, and feeding history help identify chronic protein intolerance and risk of future episodes. BioMed Central

B) Bedside / manual assessments

6. Mental status scoring (e.g., AVPU/Glasgow Coma Scale).
   Simple, repeated checks track encephalopathy and guide urgent treatment decisions. BioMed Central

7. Bedside neurologic checks for ataxia and asterixis.
   Shaky gait or flapping tremor can suggest metabolic encephalopathy during an episode. PMC

8. Diet and trigger review.
   A structured checklist of recent illness, fasting, high-protein intake, new medicines (e.g., valproate), surgery, or intense exercise helps pinpoint precipitating causes. BioMed Central

9. Family history and inheritance counseling.
   As an autosomal recessive disorder, asking about affected siblings, neonatal deaths, or consanguinity supports the diagnostic pathway. MedlinePlus

C) Laboratory and pathological tests

10. Plasma ammonia (urgent).
    This is the key test. A high plasma ammonia confirms hyperammonemia and demands immediate treatment while evaluation continues. Labs should process the sample on ice promptly to avoid false results. BioMed Central

11. Plasma amino acids (quantitative).
    Typical profile in CPS1 deficiency: low citrulline and often low arginine, sometimes high glutamine, reflecting a block at the first step of the urea cycle. MSD Manuals

12. Urine orotic acid.
    Low or normal orotic acid supports CPS1 deficiency (and NAGS deficiency), helping to distinguish from OTC deficiency, which usually has high orotic acid. ltd.aruplab.com+1

13. Plasma/urine organic acids and additional metabolic panels.
    These help exclude other causes of hyperammonemia and look for secondary clues. ltd.aruplab.com

14. Arterial/venous blood gas and electrolytes.
    Often show respiratory alkalosis early (from rapid breathing) and later metabolic changes with severe illness. MSD Manuals

15. Liver function tests and urea (BUN).
    Urea may be low in urea cycle disorders, and liver enzymes help rule out primary liver failure. PMC

16. CPS1 gene testing (molecular).
    Sequencing and deletion/duplication analysis confirm the diagnosis, define the exact variants, permit carrier testing, and guide family counseling. MedlinePlus

17. Liver enzyme assay (rarely needed).
    Measuring CPS1 activity in a liver biopsy is possible but usually reserved for unclear genetic results because the test is invasive and specialized. Urea Cycle Disorders Consortium

18. Expanded newborn screening (context).
    Most newborn programs do not directly detect CPS1 deficiency; a normal screen does not exclude it if the baby is symptomatic. Clinicians still check ammonia urgently. (Guidelines emphasize immediate ammonia testing for any sick newborn.) BioMed Central

D) Electrodiagnostic tests

19. Electroencephalogram (EEG).
    Used in encephalopathy or seizures to assess brain function and help manage status epilepticus while ammonia is being lowered. BioMed Central

20. Evoked potentials or other neurophysiology (select cases).
    Not routine, but may be used in complex neurological assessments after severe crises. ScienceDirect

E) Imaging tests

21. Brain MRI.
    Looks for cytotoxic edema and injury patterns linked to hyperammonemia; helps with prognosis and rehab planning after a crisis. BioMed Central

22. Head CT (if MRI unavailable or urgent).
    Rapidly checks for brain swelling or bleeding when a patient is unstable, though it is less sensitive than MRI for metabolic injury. BioMed Central

23. MR spectroscopy (advanced centers).
    May show elevated glutamine/glutamate peaks during hyperammonemia; this supports the metabolic diagnosis and indicates brain osmotic stress. BioMed Central

24. Abdominal ultrasound (context).
    Usually normal in CPS1 deficiency but can help exclude structural liver disease when evaluating unexplained hyperammonemia. BioMed Central

Non-pharmacological treatments (therapies & other measures)

1. Low-protein, carefully measured diet.
   Purpose: Reduce the amount of nitrogen entering the body so less ammonia is produced.
   Mechanism: Protein contains amino acids that release ammonia when broken down; limiting total protein (while still meeting essential needs) lowers ammonia generation. Diet is individualized by metabolic specialists and adjusted as a child grows or an adult’s needs change. Essential amino acids and calories are balanced to avoid malnutrition. NCBI+1

2. High-calorie “protein-sparing” nutrition during illness.
   Purpose: Prevent the body from breaking down its own muscle (catabolism), which releases ammonia.
   Mechanism: Extra glucose (often IV dextrose) and sometimes lipids give energy so the body doesn’t burn protein. This helps stabilize ammonia until medicines and dialysis work. Çocuk Metabolizma+1

3. Enteral formulas with essential amino acids.
   Purpose: Meet growth and tissue repair needs without excess nitrogen.
   Mechanism: Special formulas provide essential amino acids and calories while limiting total nitrogen load; they are often combined with citrulline supplementation in proximal UCDs like CPS1 deficiency. oslo-universitetssykehus.no+1

4. Emergency (“sick-day”) protocol.
   Purpose: Act early at the first sign of infection, fasting, vomiting, or mental change to stop ammonia from rising.
   Mechanism: Rapid start of high-calorie intake, temporary protein stop, prompt ammonia level checks, and early hospital care (IV dextrose ± lipids; consider dialysis if ammonia very high or not falling). Çocuk Metabolizma+1

5. Hemodialysis or continuous renal replacement therapy (CRRT) for severe hyperammonemia.
   Purpose: Quickly remove ammonia from blood in life-threatening situations.
   Mechanism: Blood is filtered through a machine; hemodialysis/hemodiafiltration lowers ammonia fastest and is preferred when levels are very high or not falling quickly with medicines. AJKD+2e-imd.org+2

6. Regular monitoring and early lab checks.
   Purpose: Keep ammonia and amino acids in target ranges to prevent brain injury.
   Mechanism: Scheduled blood tests (ammonia, amino acids, nutrition labs) allow fast dietary and medication adjustments to maintain metabolic stability. oslo-universitetssykehus.no

7. Avoidance of known triggers.
   Purpose: Prevent sudden ammonia spikes.
   Mechanism: Avoid prolonged fasting, dehydration, heavy protein loads, certain drugs that raise ammonia (notably valproate), and treat constipation/infections promptly. Dove Medical Press

8. Vaccination & infection prevention.
   Purpose: Reduce illness-related catabolic stress that can trigger crises.
   Mechanism: Routine vaccines and good hygiene lower infection risk; less catabolism means less ammonia. oslo-universitetssykehus.no

9. Family education and emergency letter.
   Purpose: Ensure caregivers and local clinicians know exactly what to do in a crisis.
   Mechanism: Written plans (carry an emergency letter/bracelet) speed correct treatment and reduce delays in dialysis when needed. Çocuk Metabolizma

10. Genetic counseling and newborn/relative testing.
    Purpose: Clarify inheritance, guide family planning, and identify at-risk relatives early.
    Mechanism: Molecular diagnosis enables targeted testing and early management to prevent brain injury in affected newborns. NCBI

(There are further supportive measures used by teams—neuroprotection in ICU, careful reintroduction of protein after crisis, occupational/physical therapy for developmental support, and school plans. Core mechanisms remain “lower ammonia production, increase ammonia removal, act early.”) PMC

---

Drug treatments

Important: Nitrogen-scavenger drugs are essential add-ons to diet; some are for chronic control, others for acute rescue. Always use under a metabolic specialist.

1) Glycerol phenylbutyrate (brand: RAVICTI®).
Class & purpose: Nitrogen-binding agent for chronic management of UCDs in patients who cannot be managed by diet alone (not for acute hyperammonemia). It must be used with protein restriction and sometimes amino acid supplements.
Dose & timing: Oral liquid taken 3 times daily with dose individualized by body surface area and ammonia control; labels detail dosing for age groups.
Mechanism: Converted to phenylbutyrate → phenylacetate, which binds glutamine-nitrogen to form phenylacetylglutamine, excreted in urine—an “alternate pathway” to remove nitrogen.
Key side effects: GI symptoms, fatigue, abnormal labs; risk of high phenylacetic acid if overdosed; not indicated for NAGS deficiency treatment. Not for acute crises. FDA Access Data+2FDA Access Data+2

2) Sodium phenylbutyrate (brand: BUPHENYL®; also taste-masked PHEBURANE® pellets).
Class & purpose: Oral nitrogen-binding drug for chronic control of hyperammonemia due to UCDs.
Dose & timing: Tablets/powder with weight/age-based dosing; PHEBURANE® provides calibrated oral pellets to improve palatability and adherence.
Mechanism: Phenylbutyrate is converted to phenylacetate, then conjugates with glutamine to form urinary phenylacetylglutamine, removing two nitrogens per molecule.
Key side effects: Menstrual changes, edema, low potassium, irregular labs, taste/smell issues; overdose can cause neurotoxicity (phenylacetic acid). Combine with diet ± arginine/citrulline as directed. FDA Access Data+1

3) Sodium phenylacetate + sodium benzoate IV (brand: AMMONUL®; and similar labeled injections).
Class & purpose: Intravenous rescue nitrogen-binding therapy for acute hyperammonemia in UCDs, used in hospital often alongside dialysis if needed.
Dose & timing: IV loading and maintenance infusions with careful monitoring; oral scavengers are usually held while AMMONUL is given.
Mechanism: Phenylacetate binds glutamine; benzoate binds glycine—both create conjugates (phenylacetylglutamine and hippurate) excreted in urine, carrying nitrogen out rapidly.
Key side effects: Vomiting, hyperglycemia, low potassium, neurological effects; requires strict dosing and close labs. FDA Access Data+1

4) L-citrulline (amino acid supplement; medical food).
Class & purpose: Amino acid substrate used mainly in proximal UCDs like CPS1 deficiency to “bypass” the early block and carry nitrogen as argininosuccinate downstream.
Dose & timing: Oral dosing is individualized; often divided doses daily with monitoring of amino acid profiles.
Mechanism: Provides citrulline, which—together with aspartate—forms argininosuccinate, enabling some nitrogen disposal and boosting arginine availability for growth. Evidence suggests citrulline is generally preferred to arginine in CPS1/OTC deficiencies.
Side effects: Usually well tolerated; mild GI symptoms. Wiley Online Library+1

5) L-arginine (amino acid supplement; medical food).
Class & purpose: Amino acid to maintain arginine levels and support urea cycle flux; more critical in distal UCDs, but may be used per specialist guidance.
Dose & timing: Oral or IV (ICU) with lab-guided targets (e.g., plasma arginine 70–120 µmol/L per guideline).
Mechanism: Supports protein synthesis and nitric oxide pathways; in some settings supplies substrate for urea cycle steps beyond the block.
Caution: Arginine is contraindicated in arginase (ARG1) deficiency; choice between arginine vs. citrulline depends on the specific UCD and phenotype. oslo-universitetssykehus.no

6) Carglumic acid (N-carbamylglutamate; brand: Carbaglu®).
Class & purpose: NAG analog that activates CPS1—definitive drug for NAGS deficiency; its routine benefit in CPS1 deficiency is limited and case-dependent.
Dose & timing: High oral loading then maintenance in acute settings per specialist; sometimes tried emergently when diagnosis unclear to distinguish NAGS deficiency.
Mechanism: Replaces missing N-acetylglutamate to turn CPS1 “on.” In true CPS1 enzyme defects, response is generally poor, but select cases with residual activity have been reported. BioMed Central

(Other supportive hospital medicines—like antiemetics, laxatives, insulin for hyperglycemia while giving dextrose, and cerebral edema precautions—are protocol-based and adjunctive to the core therapies above.) Dove Medical Press

Why multiple options? Oral nitrogen-scavengers keep ammonia controlled day to day; IV AMMONUL treats dangerous spikes; citrulline/arginine supply substrates for the damaged pathway; carglumic acid is primarily for NAGS deficiency, not classic CPS1 deficiency. FDA Access Data+2FDA Access Data+2

---

Dietary molecular supplements

(These are commonly used medical-nutrition components under specialist guidance. Doses are individualized; examples below explain function and mechanism.)

1. Essential amino acid mixes: provide indispensable amino acids while keeping total nitrogen low; supports growth and repair without excess ammonia production. oslo-universitetssykehus.no

2. Citrulline powder (see drug section): functions as a nitrogen carrier in proximal UCDs; mechanism is substrate supplementation to form argininosuccinate and excrete nitrogen. Wiley Online Library

3. Arginine powder (see drug section): maintains arginine pool and downstream pathways when indicated; mechanism is replenishment of a semi-essential amino acid during treatment. oslo-universitetssykehus.no

4. Calorie modules (glucose polymers): add carbohydrate calories to spare protein breakdown; mechanism is preventing catabolism that releases ammonia. Çocuk Metabolizma

5. Medium-chain triglyceride (MCT) or standard lipid modules: provide energy density that also spares protein; mechanism is alternative non-nitrogen calories during stability or illness. Çocuk Metabolizma

6. Micronutrient/vitamin supplementation: supports general metabolism and growth when total protein is restricted; mechanism is preventing nutrient deficiencies from specialized diets. oslo-universitetssykehus.no

7. Fiber and laxatives (as needed): reduce constipation, which can increase ammonia from gut bacteria; mechanism is decreasing intestinal ammonia generation and absorption. Dove Medical Press

8. Probiotics/antibiotics (case-by-case): sometimes used to reduce ammonia-producing gut flora; mechanism is lowering bacterial urease activity. Use only per specialist protocols. Dove Medical Press

9. Electrolyte solutions/oral rehydration: maintain hydration during illness to prevent catabolic stress; mechanism is supporting circulation and renal clearance of nitrogen conjugates. Çocuk Metabolizma

10. Protein-free modular formulas for infants/children: allow precise control of protein while maintaining adequate calories and fluids. oslo-universitetssykehus.no

---

Regenerative, stem-cell, and immunity booster drugs

There are no proven “immunity booster” drugs that treat CPS1 deficiency. The main disease-modifying option today is liver transplantation, which replaces the defective enzyme source. Hepatocyte transplantation and gene therapy (AAV or mRNA) are investigational and not standard of care yet. Good immune protection comes from routine vaccination and preventing infections to avoid catabolic crises. PMC+1

Investigational/advanced approaches you may hear about (research only):
• AAV gene therapy or mRNA delivery to restore CPS1 expression—studies are ongoing.
• Auxiliary/partial liver transplantation strategies in select centers.
• Hepatocyte (cell) transplantation as a bridge.
These are not approved medications and should be considered only in clinical trials or specialized programs. Urea Cycle Disorders Consortium

---

Surgeries

1) Orthotopic liver transplantation (deceased donor).
Why: Definitive, curative treatment for CPS1 deficiency because the new liver provides normal CPS1. It is considered for severe or recurrent hyperammonemia or poor metabolic control despite optimal therapy. Survival and neurocognitive outcomes are generally good in modern series. PMC+1

2) Living-donor liver transplantation.
Why: Offers earlier timing and shorter wait; used frequently in children. Outcomes are favorable in experienced centers. Donor evaluation ensures safety. Frontiers+1

3) Auxiliary (partial) orthotopic liver transplantation (APOLT).
Why: Implant a partial graft while retaining part of native liver; considered in select cases to provide enzyme activity while preserving native tissue. PMC

4) Temporary hemodialysis catheter placement.
Why: Provides immediate access for hemodialysis/hemofiltration during acute hyperammonemic coma, which rapidly lowers ammonia. AJKD

5) Gastrostomy tube (G-tube) placement.
Why: Ensures reliable delivery of nutrition, citrulline/medications, and sick-day feeds in infants/children with feeding issues—preventing catabolism and crises. Çocuk Metabolizma

---

Prevention strategies

1. Keep to your prescribed low-protein diet and calorie plan every day. NCBI

2. Never fast for long; have a sick-day plan and emergency letter. Çocuk Metabolizma

3. Take nitrogen-scavenger medicines exactly as directed; refill on time. FDA Access Data

4. Use citrulline/arginine supplements as prescribed; don’t self-adjust. oslo-universitetssykehus.no

5. Get vaccinations on schedule to lower infection risk. oslo-universitetssykehus.no

6. Treat constipation and dehydration early; both raise ammonia risk. Dove Medical Press

7. Avoid valproate and other medicines known to raise ammonia unless a specialist approves. Dove Medical Press

8. Have a dialysis-capable center identified in your emergency plan if you live far from a metabolic unit. e-imd.org

9. Monitor labs as scheduled; small adjustments prevent big crises. oslo-universitetssykehus.no

10. Seek genetic counseling for family planning and testing at-risk relatives. NCBI

---

When to see a doctor (or go to the ER)

Seek urgent care if there is vomiting, refusal to eat, unusual sleepiness, confusion, irritability, poor coordination, new tremor, seizures, or any mental status change—especially during infection or after a high-protein meal. These can signal rising ammonia and require immediate blood tests, IV dextrose, consideration of AMMONUL, and early dialysis if levels are very high or not falling quickly. PMC+2FDA Access Data+2

---

What to eat and what to avoid

Eat: the prescribed amount of protein (not zero), your special formula/medical foods, ample carbohydrates and fats for energy, and regular meals/snacks to avoid fasting. Hydrate well every day. oslo-universitetssykehus.no

Avoid: excess protein portions, skipping meals/fasting, and self-starting over-the-counter supplements without your clinic’s approval. During illness, temporarily stop natural protein per your emergency plan and switch to high-calorie feeds until reviewed. Çocuk Metabolizma

---

Frequently asked questions

1. Is CPS1 deficiency curable?
   A liver transplant replaces the missing enzyme and is considered curative for the metabolic defect, though patients still need routine transplant follow-up and medicines. PMC

2. Why is ammonia so dangerous?
   Ammonia crosses into the brain and causes swelling and energy failure; fast removal prevents permanent injury. PMC

3. Can I just avoid protein completely?
   No. You need some protein for growth and repair; your team sets a safe amount plus special amino acids. oslo-universitetssykehus.no

4. What’s the difference between RAVICTI and BUPHENYL/PHEBURANE?
   All deliver phenylbutyrate (a nitrogen-scavenger). RAVICTI is a liquid pro-drug with 3-times-daily dosing; BUPHENYL is tablets/powder; PHEBURANE is taste-masked pellets. Choice depends on age, tolerance, and insurance. FDA Access Data+2FDA Access Data+2

5. Why isn’t RAVICTI used for emergencies?
   It works for chronic control; acute crises need rapid measures like AMMONUL and dialysis. FDA Access Data+1

6. Do all CPS1 patients take citrulline?
   Often yes, because it helps carry nitrogen past the early block, but dosing is individualized; some may also get arginine. Wiley Online Library

7. Is carglumic acid (Carbaglu) for CPS1 deficiency?
   It is definitive for NAGS deficiency. In true CPS1 enzyme defects, benefit is limited; specialists may trial it if diagnosis is uncertain or residual activation is suspected. BioMed Central

8. What ammonia level is “dangerous”?
   Any rise with symptoms is concerning; many guidelines advise early dialysis if levels are very high (e.g., ≥200–500 μmol/L depending on age) or not falling quickly after starting treatment. Dove Medical Press+1

9. Can adults be diagnosed later in life?
   Yes—partial enzyme function can present later, often during stress (infection, postpartum period, high-protein intake). SpringerOpen

10. Will I need treatment forever?
    Without transplant, lifelong diet, medicines, and monitoring are needed to keep ammonia safe. NCBI

11. How good are transplant outcomes?
    Survival rates after UCD transplant are high, and metabolic correction is durable in most reports. ScienceDirect+1

12. Can I exercise?
    Yes—light to moderate activity is fine; avoid extreme fasting or heavy bodybuilding protein loads. Coordinate plans with your clinic. NCBI

13. Are there medications I should avoid?
    Valproate is a classic example; always check with your clinic before new medicines. Dove Medical Press

14. Could a future gene therapy help?
    Research is ongoing (AAV, mRNA). Not yet standard. Urea Cycle Disorders Consortium

15. What should I carry with me?
    An emergency letter, medication list, and contact numbers; consider a medical alert bracelet. Çocuk Metabolizma

Disclaimer: Each person’s journey is unique, treatment plan, life style, food habit, hormonal condition, immune system, chronic disease condition, geological location, weather and previous medical  history is also unique. So always seek the best advice from a qualified medical professional or health care provider before trying any treatments to ensure to find out the best plan for you. This guide is for general information and educational purposes only. Regular check-ups and awareness can help to manage and prevent complications associated with these diseases conditions. If you or someone are suffering from this disease condition bookmark this website or share with someone who might find it useful! Boost your knowledge and stay ahead in your health journey. We always try to ensure that the content is regularly updated to reflect the latest medical research and treatment options. Thank you for giving your valuable time to read the article.

The article is written by Team RxHarun and reviewed by the Rx Editorial Board Members

Last Updated: November 10, 2025.

PDF Documents For This Disease Condition References