Below is some information about the chromosome conditions that are screened for by _percept_ NIPT.

Chromosome conditions

Our genetic counselling team can provide further information about testing for these conditions. 

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### Down syndrome (trisomy 21)
Down syndrome is caused by an extra copy of chromosome 21 (three copies instead of the usual two). It occurs at the time of conception and is usually a random event. People with Down syndrome have some degree of intellectual disability and may have other health and developmental concerns.  
More information: [Down syndrome Australia](https://www.downsyndrome.org.au/about-down-syndrome/what-is-down-syndrome/)


### Edwards syndrome (trisomy 18)
Edwards syndrome is caused by an extra copy of chromosome 18 (three copies instead of the usual two). Babies born with Edwards syndrome can have severe intellectual and physical problems. Many only survive a few weeks, while others may live beyond one year.  
More information: [Raising children network](https://raisingchildren.net.au/guides/a-z-health-reference/trisomy-18)


### Patau syndrome (trisomy 13)
Patau syndrome is caused by an extra copy of chromosome 13 (three copies instead of the usual two). Pregnancies with Patau syndrome often miscarry. If babies are born with Patau syndrome, survival varies from a few weeks, to beyond one year.  
More information: [Raising children network](https://raisingchildren.net.au/guides/a-z-health-reference/trisomy-13)

The most commonly seen chromosome conditions in pregnancy are those involving chromosome 21, 18 or 13. However, other chromosomes can also show changes in number (e.g. three copies of chromosome number 16 instead of the usual two). These conditions are rare, but can be associated with an increased chance of miscarriage and other pregnancy complications.

##### Pertile, M. D., Halks-Miller, M., Flowers, N., Barbacioru, C., Kinnings, S. L., Vavrek, D., ... & Bianchi, D. W. (2017). Rare autosomal trisomies, revealed by maternal plasma DNA sequencing, suggest increased risk of feto-placental disease. Science translational medicine, 9(405).  
##### Scott, F., Bonifacio, M., Sandow, R., Ellis, K., Smet, M. E., & McLennan, A. (2018). Rare autosomal trisomies: Important and not so rare. Prenatal diagnosis, 38(10), 765-771.)

There are some rare conditions that are caused by a change in the structure of a chromosome This is where a piece of the chromosome may be missing or extra (deleted or duplicated).

One example are chromosome translocations.

A translocation is where a piece of one chromosome is exchanged with another chromosome. In many cases, the exchange of genetic material is balanced – meaning no loss or gain of DNA (a balanced translocation). People who carry a balanced translocation usually have no health problems caused by the change. However, complications can arise if a pregnancy carries an unbalanced form of translocation (where some DNA is extra or lost).

Discussion with our laboratory is required before using _percept_ NIPT to screen pregnancies for an unbalanced translocation.

##### Flowers, N. J., Burgess, T., Giouzeppos, O., Shi, G., Love, C. J., Hunt, C. E., ... & Pertile, M. D. (2020). Genome-wide noninvasive prenatal screening for carriers of balanced reciprocal translocations. Genetics in Medicine, 22(12), 1944-1955)

People have 23 pairs of chromosomes. The 23rd pair are known as the sex chromosomes, X and Y. The X and Y chromosomes determine if a baby will be male or female. A male has one X chromosome and one Y chromosome (XY) and a female has two X chromosomes (XX).

A sex chromosome condition is caused by a change in the number of the X and/or Y chromosomes. For example, babies with Turner syndrome are females who only have one X chromosome (X instead of XX). Another example is Klinefelter syndrome. These babies are male, but carry an extra X chromosome (XXY instead of XY).

Sex chromosome conditions are quite common in the population and may be associated with physical and/or developmental problems. These conditions are usually milder than other chromosome conditions and they are often not recognized at birth.  
More information: [Australian X and Y spectrum support](https://axys.org.au/)

Chromosome conditions

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