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Disease Profile

Chromosome 18p tetrasomy

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

1-9 / 1 000 000

US Estimated

Europe Estimated

Age of onset





Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Tetrasomy 18p; Tetrasomy chromosome 18p; Isochromosome 18p


Chromosome Disorders; Congenital and Genetic Diseases


Chromosome 18p tetrasomy is a chromosomal disorder that affects many parts of the body. It occurs when the short arm of chromosome 18 (18p) appears four times (tetrasomy) rather than the normal two times in cells of the body.[1][2] The symptoms of chromosomy 18p tetrasomy vary from case to case but may include abnormalities of the head and face (craniofacial) area, malformations of the spine, hands, and/or feet, neuromuscular abnormalities, kidney malformations, intellectual disability, speech delays, and behavioral abnormalities. In most cases, chromosome 18p tetrasomy is the result of a spontaneous (de novo) genetic change (mutation) early in fetal development during pregnancy. Although there is no specific treatment or cure for chromosome 18p tetrasomy, there are ways to manage the symptoms. A team of doctors or specialists is often needed to figure out the treatment options for each person.[1][3]


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.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Abnormality of neuronal migration
Long philtrum
Abnormally small skull
Decreased circumference of cranium
Decreased size of skull
Reduced head circumference
Small head circumference

[ more ]

30%-79% of people have these symptoms
Eye folds
Prominent eye folds

[ more ]

Low-set, posteriorly rotated ears
5%-29% of people have these symptoms
Downslanted palpebral fissures
Downward slanting of the opening between the eyelids
Facial asymmetry
Asymmetry of face
Crooked face
Unsymmetrical face

[ more ]

Gait disturbance
Abnormal gait
Abnormal walk
Impaired gait

[ more ]

Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific

[ more ]

Large hands
large hand
Narrow mouth
Small mouth
Short nose
Decreased length of nose
Shortened nose

[ more ]

Fainting spell
Thin vermilion border
Decreased volume of lip
Thin lips

[ more ]



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

    Learn more

    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

    • MedlinePlus Genetics contains information on Chromosome 18p tetrasomy. This website is maintained by the National Library of Medicine.
    • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

      In-Depth Information

      • The Chromosome 18 Clinical Research Center provides clinical management guidelines for people with different disorders involving chromosome 18, including Chromosome 18p tetrasomy.
      • 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.
      • 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 Chromosome 18p tetrasomy. Click on the link to view a sample search on this topic.


        1. Chromosome 18, Tetrasomy 18p. National Organization for Rare Disorders (NORD). 2009; https://rarediseases.org/rare-diseases/chromosome-18-tetrasomy-18p/.
        2. Tetrasomy 18p. Chromosome 18 Registry and Research Society. 12/9/2015; https://www.chromosome18.org/tetrasomy-18p/.
        3. Courtney Sebold, Elizabeth Roeder, Marsha Zimmerman, Bridgette Soileau, Patricia Heard,1 Erika Carter, Martha Schatz, W. Abraham White, Brian Perry, Kent Reinker, Louise O’Donnell, Jack Lancaster, John Li, Minire Hasi, Annice Hill, Lauren Pankratz, Daniel E. Hale, Jannine D. Cody. Tetrasomy 18p: Report of the Molecular and Clinical Findings of 43 Individuals. American Journal of Medical Genetics. June 2010; 152A:2164-2172. https://www.ncbi.nlm.nih.gov/pubmed/20803640.