What is trisomy 22?

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Last updated: September 21, 2026 • View editorial policy

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What is Trisomy 22?

Trisomy 22 is a rare chromosomal disorder characterized by the presence of an extra copy of chromosome 22, occurring in two forms: complete (non-mosaic) trisomy 22, which is typically lethal in early pregnancy or infancy, and mosaic trisomy 22, which has variable clinical severity depending on the percentage of trisomic cells and is compatible with survival beyond infancy.

Epidemiology and Survival

Trisomy 22 is the third most common autosomal trisomy in spontaneous abortions, occurring in approximately 0.4% of all clinically recognized pregnancies 1. Complete non-mosaic trisomy 22 is extremely rare in live births, with only 29 liveborn cases reported as of 2014, and most affected children die before one year of age 1. The mosaic form is even rarer, with only about 25 postnatal cases described in the literature 2.

Genetic Origin

The extra chromosome 22 originates predominantly during maternal meiosis, with over 96% of errors arising during oogenesis 3. Approximately 90% of these errors occur during the first meiotic division 3. Failure to recombine during meiosis contributes significantly to the nondisjunction event 3.

Clinical Features

Complete (Non-Mosaic) Trisomy 22

The phenotype includes 4, 1:

  • Intrauterine growth retardation (IUGR)
  • Microcephaly and cranial abnormalities
  • Facial dysmorphisms: broad flat nasal bridge, epicanthal folds, ocular hypertelorism
  • Ear anomalies: microtia, dysmorphic ears
  • Cleft lip and/or palate (variable)
  • Webbed neck
  • Congenital heart defects: involving anomalous great vessels
  • Anorectal and renal anomalies: dysplastic kidneys
  • Digital malformations: hypoplastic distal digits with thumb anomalies
  • Single umbilical artery
  • Genital anomalies

Mosaic Trisomy 22

The mosaic form presents with milder and more variable features 5, 2, 6:

  • Facial and body asymmetry (characteristic finding)
  • Cardiac defects: including atrial septal defects
  • Growth failure and short stature
  • Developmental delay and cognitive disability (variable degrees)
  • Delayed puberty
  • Hearing loss
  • Cryptorchidism
  • Hypotonic muscle

The severity of the phenotype in mosaic cases directly correlates with the percentage of trisomic cells present 6.

Diagnostic Considerations

Important Pitfall: Negative Selection in Blood

A critical caveat in diagnosing trisomy 22 is that trisomic cells may be negatively selected in peripheral blood lymphocytes, leading to false-negative results or underestimation of mosaicism 7. When clinical suspicion remains high despite normal blood karyotype, skin fibroblast culture should be performed to detect the aberration 7.

Diagnostic Algorithm

For suspected trisomy 22:

  1. Initial karyotype analysis from peripheral blood (minimum 550-band resolution) 7
  2. If blood karyotype is normal but clinical features suggest chromosomal abnormality: obtain skin fibroblast culture, particularly from areas of asymmetry or hypo/hyperpigmented regions 7
  3. Prenatal diagnosis: array CGH and FISH on uncultured amniocytes provide more accurate assessment of mosaicism levels than cultured cells alone 8
  4. Tissue-specific analysis: analyze multiple tissue types when mosaicism is suspected, as the percentage varies among tissues 2

Prenatal Findings

Fetuses with high-level mosaicism for trisomy 22 may present with 8:

  • IUGR
  • Facial cleft
  • Oligohydramnios
  • Median facial cleft on ultrasound

Prognosis and Outcomes

Complete trisomy 22 manifests early embryonic or fetal lethality, with most cases resulting in spontaneous abortion 4. The rare liveborn cases with complete trisomy 22 typically die within the first year of life, often from complex heart disease and renal failure 1.

Mosaic trisomy 22 has a better prognosis with longer lifespan compared to complete trisomy 22 5. Developmental outcomes vary significantly based on the degree of mosaicism, with cases documented surviving to at least 7 years of age 5.

References

8
Research

Mosaic trisomy 22 at amniocentesis: Prenatal diagnosis and literature review.

Taiwanese journal of obstetrics & gynecology, 2019

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.