Chromosomal Abnormalities Test (Rapid Trisomies Test)

Why is rapid test for trisomies (and other aneuploidies) important?

A chromosome anomaly, abnormality or aberration reflects an atypical number of chromosomes or a structural abnormality in one or more chromosomes. There are many types of chromosome anomalies and they can be organized into two basic groups: numerical and structural anomalies, where more frequent ones are numerical anomalies or aneuploidies. A special type of aneuploidy is uniparental disomy, a disorder which occurs when a person receives two copies of a chromosome, or a part of a chromosome, from one parent and no copies from the other parent and therefore it might not be evident in overall number of chromosomes.

In only 48 hours, rapid test for trisomies allows reliable determination of most common chromosomal abnormalities: trisomies of chromosomes 13, 18, 21, X, Y, as well as uniparental disomy of chromosome 15 (UPD-15), thus significantly reducing stress that waiting for the results may cause.

What are the risk factors for trisomies?

Every woman has a risk of having a child with Down syndrome or some other chromosome aberration, but the probability of such pregnancies is even higher in the following cases:

  • If a pregnant woman is over 35 year of age (the most common risk factor)
  • If a risk higher than 1:250 has been established in the combined screening programme
  • If there is a family history of chromosomal abnormalities

In case of the above mentioned factors and increased risk, obstetrician will strongly recommend amniocentesis in the 15th week of pregnancy.

Prenatal diagnosis of chromosomal disorders

Congenital anomalies occur in 3-5% of all newborns as a result of unknown chromosomal abnormalities, complications during the pregnancy, or for some other reasons.

Amniocentesis, an invasive prenatal procedure, still remains the only certain analysis of chromosome abnormalities, including diagnosis of syndromes Down, Patau, Edwards, Klinefelter, Turner, XYY and XXX (triple X). Karyotyping methods imply waiting for the results for a rather long period of time (3-5 weeks), which makes otherwise blissful time in a woman's life, exceptionally tense, stressful, and unpleasant.

How to get tested?

Rapid test for trisomies is based on DNA extraction from amniotic fluid obtained in the procedure of amniocentesis. The isolated DNA is subjected to QF-PCR molecular analysis. Within merely 48 hours it is clear, from the (preliminary) results of the analysis, whether the most frequent chromosomal disorders (trisomies of chromosomes 13, 18 and 21) occurred.

Genos Ltd. is the first and only laboratory in Croatia which, in collaboration with maternity hospitals and reputable gynaecological clinics, carries out identification of trisomies and other abnormalities of autosomal chromosomes 13, 18 and 21, but also sex chromosomes X and Y, as well as uniparental disomy of chromosome 15 (UPD-15) by means of QF-PCR method.

Tests we offer are the following:

  • Determination of aneuploidy - analysis of 21 loci in total (5 STR loci on each of chromosomes 13, 18 and 21 and 6 STR loci on sex chromosomes X and Y)
  • Determination of uniparental disomy of the chromosome 15 (UPD-15) - analysis of 5 STR loci on the chromosome 15.

Reduce the amount of stress and uncertainty that weeks of waiting for the results cause.

Understanding of genetic risk

Aneuploidy is a disorder caused by an abnormal number of chromosomes and, in most cases, it results in termination of the developing foetus. However, there can be cases of live birth where the most common extra chromosomes among live births are 21, 18 and 13. It can occur in anaphase I of mitosis or anaphase I or II of meiosis during cell division when chromosomes do not separate properly between the two cells. Also, exchanging genetic material between two non-homologous chromosomes (crossing-over) can lead to aneuploidy. The result of the above mentioned events is imbalance of genetic material which can cause an abnormal foetal phenotype. Most common human trisomies are: Patau syndrome (trisomy of the 13th chromosome), Edwards syndrome (trisomy of the 18th chromosome), and Down syndrome (trisomy of the 21st chromosome) and they represent approximately 75% of all significant chromosome aneuploidies. Most frequent trisomies of sex chromosomes are Turner's syndrome (monosomy of X chromosome), Klinefelter's syndrome (XXY), XYY syndrome and Triple X syndrome (XXX).

Uniparental disomy of chromosome 15 (UPD-15) is a condition which occurs when a person receives two copies of a chromosome from a single parent. It can be result of heterodisomy, in which a pair of non-identical chromosomes are inherited from one parent or isodisomy, in which a single chromosome from one parent is duplicated. Considering the parent whose chromosome is inherited, there are two types of uniparental disomy: maternal and paternal uniparental disomy. In case of chromosome 15, maternal uniparental disomy causes occurrence of Prader Willi syndrome (where both allelic variants are inherited solely from the mother), and paternal uniparental disomy results in appearance of Angelman syndrome (where both allelic variants come from the father).

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