Actions for this page Listen Print. Summary Read the full fact sheet. On this page. Risk factors for trisomy conditions Trisomy 21 — Down syndrome Trisomy 18 — Edward syndrome Trisomy 13 — Patau syndrome Signs of trisomy conditions during pregnancy Diagnosis of trisomy conditions Genetic counselling and trisomy conditions Where to get help.
Risk factors for trisomy conditions The addition of an extra chromosome usually occurs spontaneously during conception. Trisomy 21 — Down syndrome In Victoria, Down syndrome affects about one in pregnancies. Some of the physical characteristics of Down syndrome may include: slight upward slant of the eyes — nearly all people with Down syndrome have a slight upward slant of the eyes. Children with Down syndrome tend to grow more slowly and are commonly smaller than other children their age.
Adults with Down syndrome are commonly smaller than adults who do not have Down syndrome. Trisomy 18 — Edward syndrome In Victoria, Edward syndrome affects about one in 1, pregnancies. Some of the characteristics of Edward syndrome may include: physical irregularity of the kidneys, ureters, heart, lungs and diaphragm cleft lip or cleft palate small skull microcephaly malformations of the hands and feet — including missing thumbs, club feet and webbing between the fingers and toes syndactyly neural tube defect, where the spinal cord, meninges and blood vessels protrude through a gap in the vertebrae myelomeningocele malformations of the sex organs.
Survival beyond the neonatal period is uncommon for babies with Edward syndrome. Trisomy 13 — Patau syndrome In Victoria, Patau syndrome affects around one in 3, pregnancies.
Some of the characteristics of Patau syndrome may include: small skull microcephaly an abnormal opening in the skull malformations of part of the brain structural defects of the eyes cleft lip or cleft palate additional toes or fingers polydactyly congenital heart disorders, such as ventricular septal defect neural tube defect, where the spinal cord, meninges and blood vessels protrude through a gap in the vertebrae myelomeningocele malformations of the sex organs. Survival beyond the neonatal period is uncommon for babies with Patau syndrome.
Signs of trisomy conditions during pregnancy Sometimes, signs of trisomy conditions may be evident during the pregnancy. Some of these signs may include: too much amniotic fluid surrounding the baby polyhydramnios only one umbilical cord artery a smaller than expected placenta the baby is small for its gestational date the baby is less active than expected congenital defects, including cleft palate or heart irregularities, are picked up during ultrasound scans.
Genetic counselling and trisomy conditions If your child has been diagnosed with a trisomy condition, it may be helpful to speak to a genetic counsellor. Figure 4. Table 1. Figure 5. Figure 6. References and Recommended Reading Antonarakis, S. Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable. Flag Content Cancel. Email your Friend. Submit Cancel. This content is currently under construction.
Explore This Subject. Chromosome Analysis. Chromosome Structure. Mutations and Alterations in Chromosomes. Chromosome Number. Chromosome Theory and Cell Division. Sex Chromosomes. Topic rooms within Chromosomes and Cytogenetics Close. No topic rooms are there.
Or Browse Visually. Other Topic Rooms Genetics. Student Voices. Creature Cast. Simply Science. Green Screen. Green Science. Bio 2. The Success Code. Why Science Matters. The Beyond. Plant ChemCast. Half are from the father and half are from the mother. But sometimes an error occurs when the 46 chromosomes are being divided in half.
An egg or sperm cell may keep both copies of chromosome number 21, instead of just 1 copy. If this egg or sperm is fertilized, then the baby will have 3 copies of chromosome number This is called trisomy Sometimes the extra number 21 chromosome or part of it is attached to another chromosome in the egg or sperm. This may cause translocation Down syndrome. This is the only form of Down syndrome that may be inherited from a parent.
A rare form is called mosaic trisomy This is when an error in cell division happens after the egg is fertilized. People with this syndrome have both normal cells and some cells with an extra chromosome number This risk increases with each year of age, especially after age But younger women are more likely to have babies than older women. So most babies with Down syndrome are born to women younger than Chromosome problems such as Down syndrome can often be diagnosed before birth.
This is done by looking at cells in the amniotic fluid or from the placenta. This is a noninvasive prenatal screening. These tests are very accurate. Fetal ultrasound during pregnancy can also show the possibility of Down syndrome. Problems from Down syndrome may not be seen with ultrasound. After birth, your baby may be diagnosed with a physical exam. The healthcare provider may also take a blood sample. This is checked in a lab to find the extra chromosome. There is no cure for Down syndrome.
But a child with Down syndrome may need treatment for problems such as:. Heart defects. About half of babies with Down syndrome have heart defects. While most fetuses with this abnormality are spontaneously aborted by the 12th week of gestation, a few have survived into the second trimester. By contrast, the chances of survival of children with mosaic trisomy 16 used to be considered bleak with most deaths occurring in early infancy.
Advances in genetic research have since shown that some children previously unidentified with mosaic trisomy 16 have no abnormalities of any sort and that the risk of miscarriage and birth defects is directly related to the number of cells carrying the chromosomal mutation.
With that being said, more than half of babies with mosaic trisomy 16 will have fetal abnormalities, including musculoskeletal defects, distinctive facial features, undersized lungs, and an atrial septal defect a hole between the upper chambers of the heart. Males will often have hypospadias in which the opening of the urethra develops on the shaft of the penis rather than at the end.
Development delays may occur but are less common than other trisomies. Trisomy 22 is the second most common chromosomal cause of miscarriages. Survival beyond the first trimester is rare in babies with full trisomy The severity of physical and organ defects is such that babies carried to term are unable to survive for more a few hours or days.
Some babies with mosaic trisomy 22 do survive. The severity of birth defects is determined by the number of cells with the mutated chromosomal copy.
Characteristic detects include heart abnormalities, kidney problems, intellectual disability, muscle weakness, and cognitive and developmental delays. Trisomy 9 is a rare disorder in which a full trisomy is usually fatal within the first 21 days of life. Newborns with trisomy 9 will have a smaller head, distinctive facial features including a bulbous nose and sloping forehead , a deformed heart, kidney problems, and often severe muscle and skeletal malformations.
Babies born with partial or mosaic trisomy 9 have a far greater chance of survival. This is especially true with mosaic trisomy 9 in which organ defects tend to be less severe and intellectual disabilities don't necessarily impede basic language, communication, or social-emotional development. Since the disorder was first identified in , few cases of mosaic trisomy 9 have been positively identified in medical literature. Klinefelter syndrome , also known as XXY syndrome, is a condition affecting males caused by an additional X chromosome.
Individuals with Klinefelter syndrome typically produce little testosterone, resulting in reduced muscle mass, facial hair, and body hair. Characteristic symptoms include small testicles, delayed development, breast enlargement gynecomastia , and reduced fertility.
Some people with Klinefelter syndrome may also have learning disabilities, which are typically language-oriented, although intelligence will usually be normal. Testosterone replacement therapy is often used to treat the disorder alongside assisted fertility treatments for those wanting to father children.
Some females are born with triple X syndrome, involving an extra X chromosome. Triple X syndrome, also known as XXX syndrome, is not associated with physical features and often causes no medical symptoms at all. A small proportion of those affected may have menstrual irregularities as well as learning disabilities, delayed speech, and compromised language skills. However, most will develop normally and without impediment. Most males born with an extra Y chromosome have no distinctive physical features or medical issues.
If anything, individuals with XYY syndrome can sometimes be taller than average and may have an increased risk of learning disabilities, as well as delayed speech and language skills. The impairment, if any, tends to be mild. Most adults with XYY syndrome have normal sexual development and are able to conceive children.
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