National Center for Advancing and Translational Sciences Genetic and Rare Diseases Information Center, a program of the National Center for Advancing and Translational Sciences

Methylcobalamin deficiency cbl G type



Other Names:
Homocystinuria-megaloblastic anemia, cblG complementation type; cblG; Methionine synthase deficiency
Categories:

Methylcobalamin deficiency cbl G type is a rare condition that occurs when the body is unable to process certain amino acids (building blocks of protein) properly. In most cases, signs and symptoms develop during the first year of life; however, the age of onset can range from infancy to adulthood. Common features of the condition include feeding difficulties, lethargy, seizures, poor muscle tone (hypotonia), developmental delay, microcephaly (unusually small head size), and megaloblastic anemia. Methylcobalamin deficiency cbl G type is caused by changes (mutations) in the MTR gene and is inherited in an autosomal recessive manner. Treatment generally includes regular doses of hydroxocobalamin (vitamin B12). Some affected people may also require supplementation with folates and betaine.[1][2]
Last updated: 12/3/2015

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
Learn More:
HPO ID
5%-29% of people have these symptoms
Blindness 0000618
Nystagmus
Involuntary, rapid, rhythmic eye movements
0000639
Percent of people who have these symptoms is not available through HPO
Autosomal recessive inheritance 0000007
Cerebral atrophy
Degeneration of cerebrum
0002059
Decreased methionine synthase activity 0003524
Decreased methylcobalamin 0003223
Failure to thrive
Faltering weight
Weight faltering
[ more ]
0001508
Feeding difficulties in infancy 0008872
Gait disturbance
Abnormal gait
Abnormal walk
Impaired gait
[ more ]
0001288
Generalized hypotonia
Decreased muscle tone
Low muscle tone
[ more ]
0001290
Global developmental delay 0001263
Homocystinuria
High urine homocystine levels
0002156
Hyperhomocystinemia
Elevated blood homocystine
0002160
Hypomethioninemia
Decreased plasma methionine
Decreased serum methionine
[ more ]
0003658
Infantile onset
Onset in first year of life
Onset in infancy
[ more ]
0003593
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific
Mental-retardation
[ more ]
0001249
Megaloblastic anemia 0001889
Poor coordination 0002370
Seizure 0001250
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Last updated: 7/1/2020

Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

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.

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


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 Methylcobalamin deficiency cbl G type. 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 Methylcobalamin deficiency cbl G type. 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. Nuria Carrillo-Carrasco, MD, David Adams, MD, PhD, and Charles P Venditti, MD, PhD. Disorders of Intracellular Cobalamin Metabolism. GeneReviews. November 2013; http://www.ncbi.nlm.nih.gov/books/NBK1328/.
  2. Homocystinuria without methylmalonic aciduria. Orphanet. March 2012; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=622.