Some Important Facts about Trisomy 13 or Patau’s Syndrome

Chromosomes form the genetic makeup of a human body. All the information related to a person’s color, structure, behavior and so on are stored in these chromosomes. Therefore, it is obvious that any defect in this genetic makeup can lead to a deformity or disability in the developing child. One such chromosomal abnormality which leads to a large number of miscarriages and multiple congenital abnormalities is trisomy 13 or Patau’s syndrome.

Trisomy 13:

In general, there are 2 chromosomes in each of the 23 pairs of chromosomes in human body. However, in trisomy 13, the 13^th chromosome appears in triplet, which means there are three copies of chromosome 13.

This occurs when a part of the 13^th chromosome attaches to another chromosome at the time of formation of reproductive cells. It can happen in either the female egg or male sperm. It can also occur during very early fetal development stage. Most of the time, there is one extra full 13^th chromosome (full trisomy 13) while in some rare cases, only a part of 13th chromosome in present in third copy (partial trisomy 13). In the later case, the physical signs and symptoms can vary from the full trisomy condition.

The full trisomy 13 causes severe intellectual disability and physical abnormalities in different parts of the developing fetus. Some of the common problems that occur to such children are heart defects, brain and spinal cord defects, extra toes and fingers, cleft lip, cleft palate, weak muscle tone or poorly developed eyes.

It has been noted that children born with this syndrome die in the first days or weeks of their life. Only a few survive past their first year.

Some cases have also been found where the trisomy 13 is found only in few body cells rather than in all of them. This condition is known as Mosaic trisomy. The severity of this mosaic trisomy depends on the type and number of body cells having this defect. However, the condition is milder than the full trisomy.

Is this an inherited condition?

In most cases, this is not an inherited condition. Trisomy 13 occurs due to random events that occurred during formation of reproductive cells (eggs and sperms) in healthy parents. Due to some kind of error in cell division, reproductive cells may carry an extra number of the 13^th chromosome. If any of these eggs or sperms contributes in the formation of zygote of the baby, the developing baby will have an extra 13^th chromosome in each cell of his/her body.

However, the cases of translocation trisomy are inherited. In this condition, parents have a balanced translocation in which there is a genetic rearrangement between chromosome 13 and another chromosome. As this is balanced, the person will not carry any defect, however, they can pass this extra material from chromosome 13 to their children.

What are the risk factors of trisomy 13?

• Birth of affected child in personal or close family relations.
• Risk also increases with the age of mother, however it is not as pronounced as in Down’s (trisomy 21) or Edwards syndrome (trisomy 18).

Diagnosis of trisomy 13:

Trisomy 13 or any other chromosomal or genetic defects are detected in developing fetuses via prenatal genetic test. Most parents fear from undergoing these tests as they consider them unsafe for the mother and the child. However, a good option to consider is NIPT (Non-invasive Prenatal Test). NIPTs are safe and non-invasive test, which helps in early detection of such chromosomal abnormalities.

One such test is NACE (Non-invasive Analysis for Chromosomal Abnormalities) which has been newly launched in India. This test helps in determining the possibility of Patau’s syndrome starting from 10^th week of pregnancy onwards. Apart from Patau’s syndrome, it can also detect other trisomies such as trisomy 18 (Edward’s syndrome) and trisomy 21 (Down’s syndrome).

The important features of NACE are:

• Safe
• Risk-free
• Highly accurate
• Short turnaround time of 7-10 days
• Non-invasive

The test requires a small sample of mother’s blood to detect any cell free fetal-DNA circulating in the plasma. This examination is done via advanced bioinformatics analysis under professional guidance.

If the screening results come out to be positive, one has to go for diagnostic tests such as Amniocentesis or CVS for a definite prenatal diagnosis. Earlier, high risk women had to undergo diagnostic tests directly. They are confirmatory tests but they are invasive too and put a woman at risk of miscarriage.

Treatment:

There is no particular treatment for Patau’s syndrome. However, the medical management of the affected children depends upon the individual circumstances. Surgery is conducted for treating physical defects such as cleft lip and cleft palate. Occupational and speech therapy helps in full developmental potential. Overall, the children with Patau’s syndrome can be happy and can enrich their lives.