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Guanidinoacetate methyltransferase deficiency


Other Names:
GAMT deficiency; Cerebral creatine deficiency syndrome 2
Categories:
Guanidinoacetate methyltransferase (GAMT) deficiency is an inherited disease that affects the brain and muscles. People with this disease may begin showing symptoms from early infancy to age three. Signs and symptoms can vary but may include mild to severe intellectual disability, recurrent seizures (epilepsy), problems with speech, and involuntary movements. People with this disease may also have behavioral problems, including hyperactivity, autistic behaviors, and self-mutilation.[1]

GAMT deficiency is caused by changes (mutations) in the GAMT gene. The disease is inherited in an autosomal recessive manner. Diagnosis of the disease may be based on finding increased levels of guanidinoacetate in the urine, and the diagnosis can be confirmed with genetic testing. Treatment for the disease aims to increase the levels of creatine in the brain through supplementation with high doses of oral creatine monohydrate.[2]
Last updated: 7/11/2017
Signs and symptoms of guanidinoacetate methyltransferase (GAMT) deficiency typically become noticeable between the age of 3 months to 3 years. These symptoms typically include meeting milestones such as sitting up and walking later than expected (developmental delay), weak muscle tone (hypotonia), recurrent seizures (epilepsy), and problems coordinating movements (ataxia). As an affected individual gets older, other signs such as intellectual disability and behavior problems may become apparent. Behavior problems can include hyperactivity, autistic behaviors, and a tendency to harm oneself (self-mutilation).[2]

Symptoms of GAMT deficiency may worsen with age if a person is undiagnosed and does not receive the necessary treatment.[2] 
Last updated: 7/11/2017

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

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Medical Terms Other Names
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HPO ID
30%-79% of people have these symptoms
Intellectual disability, severe
Early and severe mental retardation
Mental retardation, severe
Severe mental retardation
[ more ] 		0010864
Poor speech 0002465
Progressive extrapyramidal movement disorder 0007153
Severe global developmental delay 0011344
5%-29% of people have these symptoms
Abnormal head movements 0002457
Aggressive behavior
Aggression
Aggressive behaviour
Aggressiveness
[ more ] 		0000718
Ataxia 0001251
Athetosis
Involuntary writhing movements in fingers, hands, toes, and feet
0002305
Atonic seizure 0010819
Autism 0000717
Bilateral tonic-clonic seizure
Grand mal seizures
0002069
Chorea 0002072
Dystonia 0001332
Focal impaired awareness seizure 0002384
Generalized myoclonic seizure 0002123
Hyperactivity
More active than typical
0000752
Self-injurious behavior
Self-injurious behaviour
0100716
1%-4% of people have these symptoms
Muscular hypotonia
Low or weak muscle tone
0001252
Percent of people who have these symptoms is not available through HPO
Autosomal recessive inheritance 0000007
Delayed speech and language development
Deficiency of speech development
Delayed language development
Delayed speech
Delayed speech acquisition
Delayed speech development
Impaired speech and language development
Impaired speech development
Language delay
Language delayed
Language development deficit
Late-onset speech development
Poor language development
Speech and language delay
Speech and language difficulties
Speech delay
[ more ] 		0000750
Global developmental delay 0001263
Hyperreflexia
Increased reflexes
0001347
Hypertonia 0001276
Infantile muscular hypotonia
Decreased muscle tone in infant
0008947
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific
Mental-retardation
[ more ] 		0001249
Myoclonus 0001336
Reduced brain creatine level by MRS 0025051
Seizure 0001250
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Last updated: 7/1/2020
Guanidinoacetate methyltransferase (GAMT) deficiency is caused by changes (mutations) in the GAMT gene. This gene provides instructions to the body to create a substance called creatine. Creatine helps the body store and use energy properly. When there is a mutation in GAMT, the body does not receive enough creatine to function. This causes body parts that use a lot of energy, such as the brain and the muscles, to not work properly.[1] In addition, when the body does not have enough GAMT, there is a buildup of a substance called guanidinoacetate. This buildup causes problems in the brain and muscles as well.[1]
Last updated: 7/11/2017
Guanidinoacetate methyltransferase (GAMT) deficiency is inherited in an autosomal recessive manner.[1] This means that both copies of the GAMT gene must be changed in order for a person to have symptoms of the disease. We inherit one copy of each gene from our mother and the other from our father.

People with only one copy of the GAMT gene that is changed are known as carriers. When two carriers of GAMT deficiency have children together, for each child there is a:
  • 25% chance that the child will have GAMT deficiency
  • 50% chance that the child will be a carrier of GAMT deficiency like the parents
  • 25% chance that the child will have two working copies of GAMT, so the child will not have GAMT deficiency and will not be a carrier.
Last updated: 7/11/2017
Guanidinoacetate methyltransferase (GAMT) deficiency can be diagnosed when guanidinoacetate is present in high levels in the urine. Doctors may also be suspicious that this disease is causing symptoms if there is shown to be a deficiency of creatine in the brain based on brain imaging. Genetic testing can then be used to confirm the diagnosis. If genetic testing is inconclusive, doctors may wish to take a sample of skin to see if the enzyme guanidinoacetate methyltransferase is working properly.[2] 
Last updated: 7/11/2017

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.
Guanidinoacetate methyltransferase (GAMT) deficiency is treated by supplementation with oral creatine monohydrate. By taking creatine orally, people with GAMT deficiency are able to supplement the amount of creatine in their systems so that the brain and muscles have more energy.[2]

People with GAMT deficiency may also be on a diet that restricts their arginine or protein intake. This is necessary so that the body creates less guanidinoacetate, which can result in the symptoms related to the buildup being less severe.[3] In order to allow the body to get enough nutrients with this diet restriction, people with GAMT deficiency may need to take a formula that has all amino acids except arginine in it.[2]

Doctors will recommend that people affected by GAMT deficiency be monitored closely to see how treatment is working for them. Treatment for GAMT deficiency can keep the symptoms of the disease from progressing, but treatment has not been shown to improve intellectual disability or developmental delay. [4][5] Treatment has been shown to help improve the coordination of movements and behavioral problems associated with GAMT deficiency.[6]

Other forms of therapy that may help people with GAMT deficiency include speech, occupational, and physical therapy. Behavioral therapy may reduce the behavioral symptoms of the disease as well.[2] 
Last updated: 7/11/2017
There is limited information about the long-term outlook for people affected with guanidinoacetate methyltransferase (GAMT) deficiency. Individuals who are diagnosed early in life and begin treatment before the onset of symptoms will likely have the best outcome. For this reason, newborn siblings of children with GAMT deficiency should begin treatment right away until it can be determined whether or not they have GAMT deficiency as well.[2] Many researchers are also hoping that GAMT deficiency can be added to newborn screening programs. These programs would test all newborns for the disease so that treatment can be started right away.[7][8][9][10]

When people are diagnosed later in life, treatment cannot reverse symptoms of the disease such as developmental delay or intellectual disability, but it can prevent the symptoms from worsening. In some cases, treatment has been shown to improve issues with movement coordination and behavioral problems.[6] Although GAMT deficiency has not been shown to reduce a person’s lifespan, it is possible that some of the symptoms of the disorder such as having multiple disabilities or seizures can impact life expectancy.[6]

There have been some side effects to treatment with oral creatine monohydrate. This treatment can cause kidney malfunction, so doctors need to closely monitor the kidney health of anyone who is taking this medication. Because GAMT deficiency affects the muscles, doctors may also want to monitor the heart function of people with this disease to make sure that it is functioning properly.[2]
Last updated: 7/11/2017

If you need medical advice, you can look for doctors or other healthcare professionals who have experience with this disease. You may find these specialists through advocacy organizations, clinical trials, or articles published in medical journals. You may also want to contact a university or tertiary medical center in your area, because these centers tend to see more complex cases and have the latest technology and treatments.

If you can’t find a specialist in your local area, try contacting national or international specialists. They may be able to refer you to someone they know through conferences or research efforts. Some specialists may be willing to consult with you or your local doctors over the phone or by email if you can't travel to them for care.

You can find more tips in our guide, How to Find a Disease Specialist. We also encourage you to explore the rest of this page to find resources that can help you find specialists.

Healthcare Resources

Related diseases are conditions that have similar signs and symptoms. A health care provider may consider these conditions in the table below when making a diagnosis. Please note that the table may not include all the possible conditions related to this disease.

Conditions with similar signs and symptoms from Orphanet
The differential diagnosis in children with a cerebral creatine deficiency includes L-Arginine:glycine amidinotransferase (AGAT) deficiency and X-linked creatine transporter deficiency. In the case of a partial cerebral creatine deficiency, argininosuccinic aciduria, citrullinemia type I, and gyrate atrophy of the choroid and retina (see these terms) should be considered.
Visit the Orphanet disease page for more information.

Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

Where to Start

  • Genetics Home Reference (GHR) contains information on Guanidinoacetate methyltransferase deficiency. This website is maintained by the National Library of Medicine.

In-Depth Information

  • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
  • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
  • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Guanidinoacetate methyltransferase deficiency. Click on the link to view a sample search on this topic.

Questions sent to GARD may be posted here if the information could be helpful to others. We remove all identifying information when posting a question to protect your privacy. If you do not want your question posted, please let us know.

  1. Guanidinoacetate methyltransferase deficiency. Genetics Home Reference. June 2015; http://ghr.nlm.nih.gov/condition/guanidinoacetate-methyltransferase-deficiency.
  2. Mercimek-Mahmutoglu S and Salomons GS. Creatine Deficiency Syndromes. GeneReviews. December 10, 2015; https://www.ncbi.nlm.nih.gov/books/NBK3794/.
  3. Stockler-Ipsiroglu S, van Karnebeek C, Longo N, Korenke GC, Mercimek-Mahmutoglu S, Marquart I, Barshop B, Grolik C, Schlune A, Angle B, Araujo HC, Coskun T, Diogo L, Geraghty M, Haliloglu G, Konstantopoulou V, Leuzzi V, Levtova A, Mackenzie J, Maranda B, Mhanni AA, Mitchell G, Morris A, Newlove T, Renaud D, Scaglia F, Valayannopoulos V, van Spronsen FJ, Verbruggen KT, Yuskiv N, Nyhan W, and Schulze A. Guanidinoacetate methyltransferase (GAMT) deficiency: outcomes in 48 individuals and recommendations for diagnosis, treatment, and monitoring. Molecular Genetics and Metabolism.. January 2014; 111(1):16-25. https://www.ncbi.nlm.nih.gov/pubmed/24268530.
  4. Cerebral Creatine Deficiency Syndrome2; CCDS2. Online Mendelian Inheritance in Man. June 18, 2014; https://www.omim.org/entry/612736.
  5. Iqbal F. Review: Human guanidinoacetate n-methyl transferase (GAMT) deficiency: A treatable inborn error of metabolism. Pakistan Journal of Pharmaceutical Sciences. November 2015; 28(6):2207-2211. https://www.ncbi.nlm.nih.gov/pubmed/26639513.
  6. Stockler S. Guanidinoacetate methyltransferase deficiency. Orphanet. December 2014; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?Expert=382.
  7. Mercimek-Mahmutoglu S, Pop A, Kanhai W, Fernandez Ojeda M, Holwerda U, Smith D, Loeber JG, Schielen PC, and Salomons GC. A pilot study to estimate incidence of guanidinoacetate methyltransferase deficiency in newborns by direct sequencing of the GAMT gene. Gene. January 2016; 575(1):127-131. https://www.ncbi.nlm.nih.gov/pubmed/26319512.
  8. Ombrone D, Giocaliere E, Forni G, Malvagia S, and Ia Marca G. Expanded newborn screening by mass spectrometry: New tests, future perspectives. Mass Spectrometry Reviews. January-February 2016; 35(1):71-84. https://www.ncbi.nlm.nih.gov/pubmed/25952022.
  9. Pitt JJ, Tzanakos N, and Nguyen T. Newborn screening for guanidinoacetate methyl transferase deficiency. Molecular Genetics and Metabolism. March 2014; 111(3):303-304. https://www.ncbi.nlm.nih.gov/pubmed/24477282.
  10. Pasquali M, Schwarz E, Jensen M, Yuzyuk T, DeBiase I, Randall H, and Longo N. Feasibility of newborn screening for guanidinoacetate methyltransferase (GAMT) deficiency. Journal of Inherited Metabolic Disease. March 2014; 37(2):231-236. https://www.ncbi.nlm.nih.gov/pubmed/24276113.