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Disease Profile

Mosaic trisomy 9

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 / 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)

Mosaic trisomy chromosome 9; Trisomy 9 mosaicism


Chromosome Disorders; Congenital and Genetic Diseases


Mosaic trisomy 9 is a chromosomal abnormality that can affect may parts of the body. In people affected by this condition, some of the body's cells have three copies of chromosome 9 (trisomy), while other cells have the usual two copies of this chromosome. The signs and symptoms vary but may include mild to severe intellectual disability, developmental delay, growth problems (both before and after birth), congenital heart defects, and/or abnormalities of the craniofacial (skull and face) region. Most cases are not inherited; it often occurs sporadically as a random event during the formation of the reproductive cells (egg and sperm) or as the fertilized egg divides. Treatment is based on the signs and symptoms present in each person.[1][2][3]


The signs and symptoms of mosaic trisomy 9 vary but may include:[1][2][3]

  • Different degrees of developmental delay and intellectual disability
  • Abnormal growth including low birth weight, failure to thrive, hypotonia (low muscle tone), and short stature
  • Characteristic craniofacial features such as microcephaly (unusually small head); a sloping forehead with narrow temples; a broad nose with a bulbous tip and "slitlike" nostrils; a small jaw; abnormally wide fontanelles at birth; cleft lip and/or palate; low-set, misshapen ears; microphthalmia (unusually small eyes) and/or short, upwardly slanting eyelid folds (palpebral fissures)
  • Vision problems
  • Congenital heart defects
  • Abnormalities of the muscles and/or bones such as congenital dislocation of the hips; abnormal position and/or limited function of the joints; underdevelopment of certain bones; and/or abnormal curvature of the spine
  • Unusually formed feet, such as club foot or "rocker bottom" feet
  • Abnormalities of the male reproductive system, including undescended testes, a small penis, and/or abnormal placement of the urinary opening
  • Kidney problems
  • Brain malformations such as hydrocephalus and/or Dandy-Walker malformation

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
Undescended testes
Undescended testis

[ more ]

Global developmental delay
Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific

[ more ]

Low-set ears
Low set ears
Lowset ears

[ more ]

Abnormally small eyeball
30%-79% of people have these symptoms
Bulbous nose
Facial cleft
Cleft of the face
Finger clinodactyly
High palate
Elevated palate
Increased palatal height

[ more ]

Hip dislocation
Dislocated hips
Dislocation of hip

[ more ]

Hypoplasia of penis
Underdeveloped penis
Hypoplastic female external genitalia
Underdeveloped female external genitalia
Intrauterine growth retardation
Prenatal growth deficiency
Prenatal growth retardation

[ more ]

Large fontanelles
Wide fontanelles
Limitation of joint mobility
Decreased joint mobility
Decreased mobility of joints
Limited joint mobility
Limited joint motion

[ more ]

Little lower jaw
Small jaw
Small lower jaw

[ more ]

Low levels of amniotic fluid
Rocker bottom foot
Rocker bottom feet
Rocker-bottom feet
Rockerbottom feet

[ more ]

Short neck
Decreased length of neck
Talipes equinovarus
Club feet
Club foot

[ more ]

Ventricular septal defect
Hole in heart wall separating two lower heart chambers
5%-29% of people have these symptoms
Abnormal fallopian tube morphology
Abnormal heart valve morphology
Abnormal liver lobulation
Abnormal lung lobation
Abnormality of the uterus
Uterine abnormalities
Uterine malformations

[ more ]

Absent spleen
Atrial septal defect
An opening in the wall separating the top two chambers of the heart
Hole in heart wall separating two upper heart chambers

[ more ]

Biparietal narrowing
Camptodactyly of finger
Permanent flexion of the finger
Cleft palate
Cleft roof of mouth
Corneal opacity
Cystic hygroma
Dandy-Walker malformation
Deep palmar crease
Deep palm line
Deep plantar creases
Deep wrinkles in soles of feet
Heart tip and four chambers point towards right side of body
Elbow dislocation
Dislocations of the elbows
Elbow dislocations

[ more ]

Endocardial fibroelastosis
Missing part of vertebrae
Horseshoe kidney
Horseshoe kidneys
Hydrops fetalis
Wide-set eyes
Widely spaced eyes

[ more ]

Abnormally close eyes
Closely spaced eyes

[ more ]

Intestinal malrotation
Abnormally small skull
Decreased circumference of cranium
Decreased size of skull
Reduced head circumference
Small head circumference

[ more ]

Smaller or shorter than typical limbs
Multiple renal cysts
Multiple kidney cysts
Patent ductus arteriosus
High levels of amniotic fluid
Prominent occiput
Prominent back of the skull
Prominent posterior skull

[ more ]

Renal dysplasia
Single umbilical artery
Only one artery in umbilical cord instead of two


Most cases of mosaic trisomy 9 occur due to a random event during the formation of the reproductive cells (egg and sperm) or after fertilization has taken place. An error in cell division (called nondisjunction) may cause some eggs or sperm to have an abnormal number of chromosomes. If an egg or sperm with an extra chromosome 9 contributes to the genetic makeup of an embryo, the embryo will have an extra copy of chromosome 9 in each cell. As the embryo grows and divides, an attempt may be made to correct the mistake by eliminating one extra chromosome 9. In people with mosaic trisomy 9, this attempt may be partly successful, leaving some cells with an extra chromosome 9 and some cells with the extra chromosome deleted (the usual chromosome number). This correction process is called trisomy rescue.[1][2]

In other cases, the egg and sperm may have a normal number of chromosomes, but an error of cell division (nondisjunction) occurs when the fertilized egg is growing and dividing. If an error occurs during one of the divisions, it can cause some cells to have an abnormal number of chromosomes. In people affected by mosaic trisomy 9, some of the body's cells have the usual two copies of chromosome 9, and other cells have three copies of this chromosome (trisomy). The percentage of cells with trisomy 9 and which parts of the body are affected vary from person to person. This leads to variability in the range and severity of symptoms.[1][2]

In rare cases, mosaic trisomy 9 is inherited from a parent with a chromosomal rearrangement called a "pericentric inversion." This occurs when a segment of chromosome 9 has broken off in two places, swiveled round 180 degrees and reinserted itself into the chromosome. If this rearrangement is considered "balanced," meaning the piece of chromosome is in a different order but no genetic material is gained or lost, it usually does not cause any symptoms or health problems. However, it can be associated with an increased risk of having children with an abnormal number or chromosomes.[1][2]


In some cases, mosaic trisomy 9 is diagnosed before birth. A pregnancy ultrasound may reveal signs and symptoms that are suggestive of a chromosomal or developmental disorder. Additional tests, such as chorionic villus sampling (CVS) or an amniocentesis, may be offered to further investigate these features. During a CVS, a tissue sample from a portion of the placenta is removed and analyzed, while amniocentesis involves the removal of a sample of fluid that surrounds the developing baby. In both tests, the fluid or tissue sample is used to obtain a picture of the baby's chromosomes, which is called a karyotype. This may reveal mosaic trisomy 9.[1][2]

In other cases, the child is not diagnosed until after birth. Mosaic trisomy 9 may be suspected after characteristic signs and symptoms are identified on physical exam. A diagnosis can be confirmed by examining the child's chromosomes from a sample of blood.[2]


Because mosaic trisomy 9 affects many different systems of the body, medical management is often provided by a team of doctors and other healthcare professionals. Treatment for this condition varies based on the signs and symptoms present in each person. For example, children with bone or muscle abnormalities and/or delayed motor milestones (i.e. walking) may be referred for physical or occupational therapy. Depending on the degree of intellectual disability, a child may require special education classes. Heart defects and cleft lip and/or palate may need to be surgically repaired. Children with hydrocephalus may be treated with certain medications and/or shunting (placement of a specialized device that drains excess fluid away from the brain). Other surgeries may be recommended depending on the nature and severity of the other features (i.e. craniofacial, muscular, skeletal, kidney, and/or reproductive system problems) and their associated symptoms.[1][2]


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 Mosaic trisomy 9. 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.
    • Unique is a source of information and support to families and individuals affected by rare chromosome disorders. Click on the link to view information about trisomy 9 mosaicism.

      In-Depth Information

      • 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 Mosaic trisomy 9. Click on the link to view a sample search on this topic.


        1. Trisomy 9 Mosaicism. Unique. 2001; https://www.rarechromo.org/information/Chromosome%20%209/Trisomy%209%20mosaicism%20FTNW.pdf.
        2. CHROMOSOME 9, TRISOMY MOSAIC. NORD. May 2008; https://www.rarediseases.org/rare-disease-information/rare-diseases/byID/1035/viewAbstract.
        3. Zen PR, Rosa RF, Rosa RC, Graziadio C, Paskulin GA.. New report of two patients with mosaic trisomy 9 presenting unusual features and longer survival. Sao Paulo Med J. December 2011; 129(6):428-432.

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