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40 years!
Last updated:
1/31/2023
Years published: 2019, 2023
NORD gratefully acknowledges Nicola Longo, MD, PhD, Chief, Division of Medical Genetics, University of Utah Health Care; Scientific and Medical Advisory Board, Association for Creatine Deficiencies, for the preparation of this report.
Summary
Arginine: glycine amidinotransferase deficiency (AGAT) is one of the three cerebral creatine deficiency syndromes (CCDS). These conditions are inborn errors of creatine metabolism which interrupt the formation or transport of creatine. Creatine is necessary to use properly adenosine triphosphate (ATP), which provides energy to all cells in the body.
The severity of AGAT varies from patient to patient. People with AGAT typically present with mild to moderate intellectual disabilities, delayed speech and may have seizure activity. Some individuals may develop autistic like behaviors. Children with AGAT may not gain weight and grow at the expected rate (failure to thrive) and have delayed development of motor skills such as sitting and walking. Affected individuals may also have weak muscle tone and tend to tire easily.
AGAT is the first step of creatine production, resulting in the formation of guanidinoacetate, the immediate precursor of creatine. Changes (mutations or pathogenic variants) in the GATM gene impair the body’s production of creatine. Out of the three CCDS, AGAT is the least reported. Affected individuals may demonstrate cerebral creatine deficiency on MR spectroscopy and low GAA in plasma.
The inheritance pattern for AGAT is autosomal recessive. Recessive genetic disorders occur when an individual inherits a non-working gene from each parent. If an individual receives one working gene and one non-working gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the non-working gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier, like the parents, is 50% with each pregnancy. The chance for a child to receive working genes from both parents is 25%. The risk is the same for males and females.
Fewer than 20 patients with AGAT have reported worldwide.
Testing in plasma is recommended by measuring the concentration of creatine (Cr), and guanidinoacetate (GAA). A positive screen for AGAT is based on plasma GAA that is low with creatine being low to normal. Urine GAA is usually low but is difficult to distinguish from normal levels.
Follow up genomic testing for pathogenic variants in the GATM gene may be ordered along with brain MRI with spectroscopy to confirm an AGAT diagnosis. MRI with spectroscopy is useful for measuring creatine levels in the brain.
Generally not required for diagnosis, but cultured skin fibroblasts may be helpful when gene sequencing test results are unclear.
Treatment
Individual diagnosed with AGAT may require the coordinated efforts of a team of specialists. A pediatrician or an adult primary care physician, neurologist, geneticist, dietician and a doctor who is familiar with metabolic disorders may need to work together to ensure a comprehensive approach to treatment. Occupational, speech, and physical therapists may be necessary to treat developmental disabilities and behavior therapy to address behavior problems.
Treatments vary with each AGAT patient. Oral creatine monohydrate is given to replenish creatine levels in the brain and other tissues in individuals with AGAT. For AGAT patients being treated with creatine monohydrate, a routine measurement of renal function should be considered to detect possible creatine-associated kidney disease (nephropathy).
Prevention of Primary Symptoms
Early treatment at the first sign of symptoms in patients with AGAT is effective in improving a patient’s quality of life. The treatment in newborn siblings of individuals with AGAT deficiency can prevent disease manifestation.
Information on current clinical trials is posted on the Internet at https://clinicaltrials.gov/. All studies receiving U.S. Government funding, and some supported by private industry, are posted on this government web site.
For information about clinical trials being conducted at the NIH Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:
Toll-free: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov
Some current clinical trials also are posted on the following page on the NORD website:
https://rarediseases.org/living-with-a-rare-disease/find-clinical-trials/
For information about clinical trials sponsored by private sources, contact:
https://www.centerwatch.com/
For information about clinical trials conducted in Europe, contact:
https://www.clinicaltrialsregister.eu/
JOURNAL ARTICLES
Stockler-Ipsiroglu S, Apatean D, Battini R, DeBrosse S, et al. Arginine: glycine amidinotransferase (AGAT) deficiency: Clinical features and long-term outcomes in 16 patients diagnosed worldwide. Mol Genet Metab. 2015; Dec;116(4):252-9.
Dunbar M. Jaggumantri S, Sargent M, Stockler-Ipsiroglu S(2), van Karnebeek CD. Treatment of X-linked creatine transporter (SLC6A8 deficiency: a systematic review of the literature and three new cases. Mol Genet Metab. 2014;112:259-74.
Stockler-Ipsiroglu S, van Karnebeek C, Longo N, Korenke GC, et all. Guanidinoacetate methyltransferase (GAMT) deficiency: outcomes in 48 individuals and recommendations for diagnosis, treatment, and monitoring. Mol Genet Metab. 2014;111:16-25.
Van de Kamp M, Mancini GM, Salomons GS. X-linked creatine transporter deficiency: clinical aspects and pathophysiology. J Inherit Metab Dis. 2014;37:715-33.
Trotier-Faurion A, Dezard S, Taran F, Valayannopoulos V, de Lonlay P, Mabondzo A. Synthesis and biological evaluation of new creatine fatty esters revealed dodecyl creatine ester as a promising drug candidate for the treatment of the creatine transporter deficiency. J Med Chem. 2013; Jun 27;56(12):5173-81.
Van de Kamp JM, Betsalel OT, Mercimek-Mahmutoglu S, Abulhoul L, et al. Phenotype and genotype in 1010 males withX-linked creatine transporter deficiency. J Med Genet. 2013; 50:463-72.
Longo N, Ardon O, Vanzo R, Schwartz E, Pasquali M. Disorders of creatine transport and metabolism. Am J Med Genet C Semin Med Genet. 2011;157C:72-8.
Rosenberg EH, Almeida LS, Kleefstra T, deGrauw RS, et all. High prevalence of SLC6A8 deficiency in X-linked mental retardation. AM J Hum Genet. 2004;75:97-105.
INTERNET
Mercimek-Andrews S, Salomons GS. Creatine Deficiency Disorders. 2009 Jan 15 [Updated 2022 Feb 10]. In: Adam MP, Everman DB, Mirzaa GM, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2022. Available from: https://www.ncbi.nlm.nih.gov/books/NBK3794/ Accessed Nov 30, 2022.
Arginine:Glycine Amidinotransferase Deficiency. Genetic Home Reference. Reviewed December 2015. https://ghr.nlm.nih.gov/condition/arginineglycine-amidinotransferase-deficiency Accessed Nov 30, 2022.
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