Laboratory Studies

In patients with citrullinemia who are symptomatic, the measurement of blood ammonia levels is the primary laboratory test in diagnosis. No other routinely obtained study provides diagnostically useful information.

Quantitative measurement of blood amino acid levels is the next immediate step. Citrulline levels are unmistakably elevated in patients with citrullinemia. In such patients, urine amino acid, urine organic acid, and urine orotic acid levels should be analyzed. Orotic acid levels in urine are abnormally elevated in citrullinemia.

Measurement of argininosuccinic acid (ASA) synthase in cultured skin fibroblasts can provide an unequivocal biochemical diagnosis.

Molecular analysis of the gene should be pursued to establish the nature of the mutation, which can be used for prenatal diagnostic studies.

In neonates who are jaundiced and have normal or mildly elevated ammonia levels, hypercholesterolemia suggests citrin deficiency.^{[12, 3]}

Imaging Studies

MRI of the brain in affected infants shows several associated abnormalities, the extent of which are helpful in predicting neurological outcomes.^{[13, 14, 15]}

Other Tests

New experimental data in a mouse model have suggested that T-cell function may be impaired in individuals with citrullinemia.^[16]

Treatment & Management

Prestes CC, Sgaravatti AM, Pederzolli CD, et al. Citrulline and ammonia accumulating in citrullinemia reduces antioxidant capacity of rat brain in vitro. Metab Brain Dis. 2006 Mar. 21(1):63-74. [QxMD MEDLINE Link].
Saheki T, Kobayashi K. Mitochondrial aspartate glutamate carrier (citrin) deficiency as the cause of adult-onset type II citrullinemia (CTLN2) and idiopathic neonatal hepatitis (NICCD). J Hum Genet. 2002. 47(7):333-41. [QxMD MEDLINE Link].
Saheki T, Song YZ, Adam MP, Ardinger HH, Pagon RA, Wallace SE, et al. Citrin Deficiency. 1993. [QxMD MEDLINE Link]. [Full Text].
Summar ML, Koelker S, Freedenberg D, et al. The incidence of urea cycle disorders. Mol Genet Biol. September-October 2013. 110:179-180. [QxMD MEDLINE Link].
Noto D, Takahashi K, Hamaguchi T, et al. A case of adult onset type II citrullinemia with portal-systemic shunt. J Neurol Sci. 2009 Mar 12. [QxMD MEDLINE Link].
Quinonez SC, Thoene JG, Adam MP, Ardinger HH, Pagon RA, Wallace SE, et al. Citrullinemia Type I. 1993. [QxMD MEDLINE Link]. [Full Text].
Waisbren SE, Cuthbertson D, Burgard P, Holbert A, McCarter R, Cederbaum S, et al. Biochemical markers and neuropsychological functioning in distal urea cycle disorders. J Inherit Metab Dis. 2018 Jul. 41 (4):657-667. [QxMD MEDLINE Link].
Yazaki M, Ikeda S, Kobayashi K, Saheki T. Therapeutic approaches for patients with adult-onset type II citrullinemia (CTLN2): effectiveness of treatment with low-carbohydrate diet and sodium pyruvate. Rinsho Shinkeigaku. 2010 Nov. 50(11):844-7. [QxMD MEDLINE Link].
Engel K, Hohne W, Haberle J. Mutations and polymorphisms in the human argininosuccinate synthetase (ASS1) gene. Hum Mutat. 2009 Mar. 30(3):300-7. [QxMD MEDLINE Link].
Marquis-Nicholson R, Glamuzina E, Prosser D, Wilson C, Love DR. Citrullinemia type I: molecular screening of the ASS1 gene by exonic sequencing and targeted mutation analysis. Genet Mol Res. 2010 Aug 3. 9(3):1483-9. [QxMD MEDLINE Link].
Diez-Fernandez C, Rüfenacht V, Häberle J. Mutations in the Human Argininosuccinate Synthetase (ASS1) Gene, Impact on Patients, Common Changes, and Structural Considerations. Hum Mutat. 2017 May. 38 (5):471-484. [QxMD MEDLINE Link].
Nagasaka H, Okano Y, Tsukahara H, et al. Sustaining hypercitrullinemia, hypercholesterolemia and augmented oxidative stress in Japanese children with aspartate/glutamate carrier isoform 2-citrin-deficiency even during the silent period. Mol Genet Metab. 2009 Jan 25. [QxMD MEDLINE Link].
Gunz AC, Choong K, Potter M, Miller E. Magnetic resonance imaging findings and neurodevelopmental outcomes in neonates with urea-cycle defects. Int Med Case Rep J. 2013 Aug 19. 6:41-8. [QxMD MEDLINE Link]. [Full Text].
Bireley WR, Van Hove JL, Gallagher RC, Fenton LZ. Urea cycle disorders: brain MRI and neurological outcome. Pediatr Radiol. 2012 Apr. 42(4):455-62. [QxMD MEDLINE Link].
Ah Mew N, Simpson KL, Gropman AL, Lanpher BC, Chapman KA, Summar ML, et al. Urea Cycle Disorders Overview. 1993. [QxMD MEDLINE Link]. [Full Text].
Tarasenko N, Gomez-Rodriguez J, McGuire PJ. Impaired T cell function in argininosuccinate synthetase deficiency. J Leukoc Biol. February 2015. 97:273-278. [QxMD MEDLINE Link].
Vara R, Dhawan A, Deheragoda M, Grünewald S, Pierre G, Heaton ND, et al. Liver transplantation for neonatal-onset citrullinemia. Pediatr Transplant. 2018 Jun. 22 (4):e13191. [QxMD MEDLINE Link].
Kimura N, Kubo N, Narumi S, et al. Liver Transplantation Versus Conservative Treatment for Adult-Onset Type II Citrullinemia: Our Experience and a Review of the Literature. Transplant Proc. 2013 Nov. 45(9):3432-7. [QxMD MEDLINE Link].
Nakamura M, Yazaki M, Kobayashi Y, Fukushima K, Ikeda S, Kobayashi K, et al. The characteristics of food intake in patients with type II citrullinemia. J Nutr Sci Vitaminol (Tokyo). 2011. 57(3):239-45. [QxMD MEDLINE Link].
Berry GT, Steiner RD. Long-term management of patients with urea cycle disorders. J Pediatr. Jan 2001. 138(1 Pt 2):S56-S62. [QxMD MEDLINE Link].
Hayakawa M, Kato Y, Takahashi R, Tauchi N. Case of citrullinemia diagnosed by DNA analysis: including prenatal genetic diagnosis from amniocytes of next pregnancy. Pediatr Int. 2003 Apr. 45(2):196-8. [QxMD MEDLINE Link].
Issa AR, Yadav G, Teebi AS. Intrafamilial phenotypic variability in citrullinaemia: report of a family. J Inherit Metab Dis. 1988. 11(3):306-7. [QxMD MEDLINE Link].
Kennaway NG, Harwood PJ, Ramberg DA, Koler RD, Buist NR. Citrullinemia: enzymatic evidence for genetic heterogeneity. Pediatr Res. 1975 Jun. 9(6):554-8. [QxMD MEDLINE Link].
Kuhara H, Wakabayashi T, Kishimoto H, et al. Neonatal type of argininosuccinate synthetase deficiency. Report of two cases with autopsy findings. Acta Pathol Jpn. 1985 Jul. 35(4):995-1006. [QxMD MEDLINE Link].
Matsuda I, Anakura M, Arashima S, Saito Y, Oka Y. A variant form of citrullinemia. J Pediatr. 1976 May. 88(5):824-6. [QxMD MEDLINE Link].
Morrow G 3rd, Barness LA, Efron ML. Citrullinemia with defective urea production. Pediatrics. 1967 Oct. 40(4):565-74. [QxMD MEDLINE Link].
Ohura T, Kobayashi K, Tazawa Y, et al. Clinical pictures of 75 patients with neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD). J Inherit Metab Dis. 2007 Apr. 30(2):139-44. [QxMD MEDLINE Link].
Saheki T, Kobayashi K, Iijima M, et al. Metabolic derangements in deficiency of citrin, a liver-type mitochondrial aspartate-glutamate carrier. Hepatol Res. 2005 Oct. 33(2):181-4. [QxMD MEDLINE Link].
Steiner RD, Cederbaum SD. Laboratory evaluation of urea cycle disorders. J Pediatr. 2001 Jan. 138(1 Suppl):S21-9. [QxMD MEDLINE Link].
Tamamori A, Fujimoto A, Okano Y, et al. Effects of citrin deficiency in the perinatal period: feasibility of newborn mass screening for citrin deficiency. Pediatr Res. 2004 Oct. 56(4):608-14. [QxMD MEDLINE Link].
Tazawa Y, Kobayashi K, Abukawa D, et al. Clinical heterogeneity of neonatal intrahepatic cholestasis caused by citrin deficiency: case reports from 16 patients. Mol Genet Metab. 2004 Nov. 83(3):213-9. [QxMD MEDLINE Link].
Walter JH, Allen JT, Holton JB. Arginosuccinate synthetase deficiency: good outcome despite severe neonatal hyperammonemia. J Inherit Metab Dis. 1992. 15(2):282-3. [QxMD MEDLINE Link].

Media Gallery

Urea cycle. Compounds that comprise the urea cycle are numbered sequentially, beginning with carbamyl phosphate. At the first step (1), the first waste nitrogen is incorporated into the cycle; also at this step, N-acetylglutamate exerts its regulatory control on the mediating enzyme, carbamyl phosphate synthetase (CPS). Compound 2 is citrulline, the product of condensation between carbamyl phosphate (1) and ornithine (8); the mediating enzyme is ornithine transcarbamylase. Compound 3 is aspartic acid, which is combined with citrulline to form argininosuccinic acid (4); the reaction is mediated by argininosuccinate (ASA) synthetase. Compound 5 is fumaric acid generated in the reaction that converts ASA to arginine (6), which is mediated by ASA lyase.

of 1

Author

Karl S Roth, MD Retired Professor and Chair, Department of Pediatrics, Creighton University School of Medicine

Karl S Roth, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Pediatrics, American College of Nutrition, American Pediatric Society, American Society for Nutrition, American Society of Nephrology, Association of American Medical Colleges, Medical Society of Virginia, New York Academy of Sciences, Sigma Xi, The Scientific Research Honor Society, Society for Pediatric Research, Southern Society for Pediatric Research

Disclosure: Nothing to disclose.

Specialty Editor Board

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Nothing to disclose.

Chief Editor

Maria Descartes, MD Professor, Department of Human Genetics and Department of Pediatrics, University of Alabama at Birmingham School of Medicine

Maria Descartes, MD is a member of the following medical societies: American Academy of Pediatrics, American College of Medical Genetics and Genomics, American Medical Association, American Society of Human Genetics, Society for Inherited Metabolic Disorders, International Skeletal Dysplasia Society, Southeastern Regional Genetics Group

Disclosure: Nothing to disclose.

Additional Contributors

Robert D Steiner, MD, FAAP, FACMG Professor (Clinical), Department of Pediatrics, University of Wisconsin School of Medicine and Public Health; Editor-in-Chief, Genetics in Medicine; Chief Medical Officer, PreventionGenetics

Robert D Steiner, MD, FAAP, FACMG is a member of the following medical societies: American Academy of Pediatrics, American Association for the Advancement of Science, American College of Medical Genetics and Genomics, American Society of Human Genetics, Society for Inherited Metabolic Disorders, Society for Pediatric Research, Society for the Study of Inborn Errors of Metabolism

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: PreventionGenetics, ACMG, Acer Therapeutics, Biomarin; Best Doctors, Health Advances, Precision for Health, PTC Therapeutics, CTX Alliance, Aeglea, Eton, Leadiant<br/>Serve(d) as a speaker or a member of a speakers bureau for: France Foundation, Medscape<br/>Received research grant from: Alexion<br/>Received income in an amount equal to or greater than $250 from: Marshfield Clinic, France Foundation, Medscape, PreventionGenetics, ACMG, Acer Therapeutics; Raptor, Retrophin/Travere, Censa; Biomarin; Best Doctors, Health Advances, Precision for Health, PTC Therapeutics, Aeglea, Leadiant<br/>Travel Support for: CTX Alliance.