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Disease Profile

49,XXXXX syndrome

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.


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)

Pentasomy X; Chromosome XXXXX syndrome; Penta-X syndrome;


Chromosome Disorders; Congenital and Genetic Diseases


The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.

Orpha Number: 11

Pentasomy X is a sex chromosome anomaly caused by the presence of three extra X chromosomes in females (49,XXXXX instead of 46,XX).

The prevalence is unknown but less than 40 cases have been described in the literature so far.

Clinical description
Pentasomy X is associated with developmental delays, short stature, craniofacial anomalies and musculoskeletal abnormalities. The craniofacial anomalies may include microcephaly, micrognathia, plagiocephaly, hypertelorism, upslanting palpebral fissures, a flat nasal bridge and ear malformations. The hands and feet are generally small and camptodactyly, clinodactyly, and radioulnar synostosis are common findings. Immunoglobulin anomalies and an increased susceptibility to infection have also been reported. Cardiovascular malformations may also be present. External genitalia are generally normal but gonadal dysfunction has been reported. Developmental profiles usually show global developmental delay and intellectual disability; however, receptive language skills are usually less severely affected than expressive language abilities.

Pentasomy X is generally thought to arise as a result of successive maternal nondisjunction during meiosis.

Visit the Orphanet disease page for more resources.


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
Low-set, posteriorly rotated ears
Muscular hypotonia
Low or weak muscle tone
30%-79% of people have these symptoms
Camptodactyly of finger
Permanent flexion of the finger
Clinodactyly of the 5th finger
Permanent curving of the pinkie finger
Global developmental delay
Wide-set eyes
Widely spaced eyes

[ more ]

Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific

[ more ]

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

[ more ]

Little lower jaw
Small jaw
Small lower jaw

[ more ]

Flat head syndrome
Flattening of skull
Rhomboid shaped skull

[ more ]

Radioulnar synostosis
Fused forearm bones
Short foot
Short feet
Small feet

[ more ]

Short stature
Decreased body height
Small stature

[ more ]

Small hand
Disproportionately small hands
Squint eyes

[ more ]

Upslanted palpebral fissure
Upward slanting of the opening between the eyelids
Wide nasal bridge
Broad nasal bridge
Broad nasal root
Broadened nasal bridge
Increased breadth of bridge of nose
Increased breadth of nasal bridge
Increased width of bridge of nose
Increased width of nasal bridge
Nasal bridge broad
Wide bridge of nose
Widened nasal bridge

[ more ]

5%-29% of people have these symptoms
Abnormal cardiac septum morphology
Abnormality of immune system physiology
Delayed puberty
Delayed pubertal development
Delayed pubertal growth
Pubertal delay

[ more ]

Hip dysplasia
Patent ductus arteriosus


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

    • Genetics Home Reference (GHR) contains information on 49,XXXXX syndrome. 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 pentasomy X.

      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 49,XXXXX syndrome. Click on the link to view a sample search on this topic.