“Trisomy 13 also known as Patau syndrome occurs due to the numerical chromosomal abnormality in which an extra copy of chromosome 13 presents with a pair.”
Or in other words, we can say,
“An extra copy of chromosome 13 present in a cell causes serious health problem is referred as trisomy 13 or Patau syndrome also known as trisomy D.”
Globally, 1 in 10,000 to 16,000 newborn babies suffer from trisomy 13, the risk of the Patau syndrome increases with the increment of maternal age. Women above 31 of age are at risk of the occurrence of trisomy 13.
The genetic basis or the chromosomal bases of the present disease was reported by Klaus Patau in 1960, though it was first reported in 1657 by Thomas Bartholin.
For his contribution to postulating the genetic basis of trisomy 13, it is named Patau syndrome as well. Besides Patau syndrome, the condition is also known as Bartholin- Patau syndrome or Pataus’s syndrome.
In the present article, we will talk about the common type of aneuploidy- trisomy 13 and related information.
Definition of trisomy 13:
“A rare form of chromosomal aberration in which an extra copy or some portion of chromosome 13 present in a genome with the pair of chromosome 13 caused by nondisjunction, is known as trisomy 13 or Patau syndrome.”
The event nondisjunction causes trisomies, so it is involved in Patau syndrome as well. This condition results in serious health and developmental issues. With a total of 47 chromosomes present in a cell in which three different chromosomes 13 are there, Patau syndrome is a congenital condition.
The fetal genetic makeup is made up of haploid sets, inherited from each parent, meaning one from the father and the other from the mother. Egg and sperm cells- germ cells are fuses to make a fetus, so 23 chromosomes from the egg and 23 from the sperm make diploid; 46 chromosomes for the offspring.
Meiosis is the process of germ cell division, when any abnormality occurs during the process of meiosis, either in meiosis 1 or meiosis 2, results in uneven distribution of chromosomes. The most common is the event of non-disjunction in which chromosomes can’t be evenly distributed. Consequently, when trisomy 13 results in the increment of genetic material.
So technically, the presence of three different chromosomes 13 causes copy number variation for that chromosome. Note that the whole event of nondisjunction occurs randomly. No clear reason for that is noted.
So the increment of genetic content or we can say copy number variation disrupts or interrupt normal development and results in severe intellectual and physical disabilities.
Types of Trisomy 13:
Much like the categorize of trisomy 18 or Edward’s syndrome, trisomy 13 can be divided into complete trisomy 13, partial trisomy, mosaic trisomy and translocation trisomy.
Translocation trisomy 13:
Usually, trisomies are non-inherited, however, approximately 20% of trisomy 13 cases originates by translocation and are inherited. Here, during the meiosis of germ cells (sperm or egg) some portion of chromosome 13 detached and translocated to some other chromosome randomly.
Hence in the fetus, along with the pair of chromosome 13, a portion of chromosome 13 also inherited into the fetus through translocation.
However, the sign and the symptom of the disease with the translocation trisomy 13 differ based on the amount of the portion of chromosome 13 translocated. But is less severe than the complete trisomy.
Mosaic trisomy 13:
In the mosaic type of trisomy 13 situation, the fetus possesses two different types of cell populations, one with the triple chromosome 13 and one with the pair of normal chromosome 13.
The sign and symptoms of disease with mosaic trisomy 13 are mild to moderate and also, it depends on how many cells contain trisomy. The mosaic trisomy 13 cases are very few.
Partial trisomy 13:
Yet, another rarest form of the Patau syndrome is the partial trisomy 13, here, only some portion of chromosome 13 inherited with the pair- not the entire chromosome. Very few cases of partial trisomy 13 are reported.
Complete trisomy 13:
Complete trisomy 13 is the most prevalent form of this condition, as we said, in this condition, three different chromosomes are present in the fetus. More than 80% of cases of Patau syndrome are complete trisomy.
Here the signs and symptoms of the condition are more severe and problematic than other forms. Much like the mosaic condition, though complete trisomy 13 is non-inherited, it occurs due to an imbalance in chromosome distribution. Thus the probability of the recurrence of trisomy 13 is very less or negligible unless one of the parents has translocation trisomy.
The severity of symptoms depends on how much amount of genetic material copied. A full penetrance of the disease shown in the complete trisomy, here I have listed some of the common symptoms. Note that mental, intellectual and developmental abnormalities are reported commonly.
- Close-set or closely located eyes
- Coloboma- a hole in the iris of the eye
- Low-set ears
- Inguinal and umbilical hernia
- Skeletal abnormalities
- Microcephaly- small head
- Small jaw (especially lower)
- Cryptorchidism- is the condition with an undescended testicle
- Absence of eyeballs
- Abnormal share of the pelvic girdle bone
- Abnormal cranial structure
- Congenital heart defects
- Cleft palate or lip
- Extra toes (polydactyly)
- Decrease muscle tone
- Breathing and feeding problem
- Congenital trigger digits
- Prominent heel
- Overlapping fingers over the thumb
- Kidney defect
- Defective head
- Low birth weight
- Underdeveloped nostrils
Trisomy 13 is one of the common types of trisomy, besides Down syndrome with serious and complicated health issues. Commonly, an infant with trisomy 13 dies immediately after birth or in a few hours. In some cases, a baby can live up to weeks, however, below 10% of babies with trisomy 13 can live up to the year.
The mortality rate of the fetus with trisomy 13- Patau syndrome is very high as like trisomy 18. However, babies with partial or mosaic trisomy 13 can live up to adulthood or above but those cases are very rare.
The majority of the cases with the complete trisomy 13 may die in a day or within a year after birth.
Pictures of trisomy 13:
Some other pictures of trisomy 13 with facial, feet or hand abnormalities are shown in the figure below,
As we explained in the previous article two common methods are most trustworthy for encountering the trisomy i.e ultrasound and genetic analysis.
The initial indication of the disease can be diagnosed using the ultrasound method in the early period of the pregnancy.
However, genetic testing or cytogenetic analysis must be required for validating the ultrasound indications.
Using the cytogenetic technique known as karyotyping, chromosomal aberrations can be encountered using GTG banding technique.
For cytogenetic analysis, amniotic fluid (the technique is called amniocentesis) or chorionic villi sample is taken and cultured for getting metaphase cells.
From the metaphase cells, chromosomes are separated using chromosome harvesting and stained using the GTG banding or G banding (Giemsa banding). Using computational software, numerical or major structural chromosomal aberrations are detected.
Another emerging genetic testing method nowadays scientists are using is known as cell-free DNA testing in which circulating fragments of fetal DNA are isolated from the mother’s blood and employed for encountering trisomy.
Though the mortality rate of Patau syndrome is high, individuals with less serious symptoms can survive in some cases if proper treatment is given in the early days. The treatment of Patau syndrome may vary on the basis of the type of symptoms shown in the individual.
For example, speech and mental treatment or therapies are given to improve patients’ psychological and mental health.
Individuals with mosaic or partial condition can live up to adulthood or more, however, the majority of patients die within a few weeks, proper treatment can help to improve patients’ health.
Surgeries can help to repair the heart defect or cleft lips.
Occupational therapy, physical treatment, psychological counseling, motor skills improvement therapy and other different approaches may help the patient.
The survival rate:
Overall, the mortality rate of trisomies is very high except, trisomy 21. Babies with trisomy 13 may die in early life, in a day or in a few weeks due to complex mental, physical and neurological problems.
Notwithstanding this, in a few cases with mild to moderate Patau syndrome can live up to a year or up to 10 years. However, extensive case, management and treatments are required.
Approximately 10 to 13% of babies with trisomy 13 may survive up to 10 years. In comparison with trisomy 21, the survival rate of Patau syndrome is very low.
Even if a patient may survive up to some extinct, he or she has to face so many mental, motor and physical problems, unlike the normal child, their life is not at all normal.
Suggestions for parents:
The burden of genetic abnormalities or congenital abnormalities increases globally, due to a lack of knowledge and proper guidance, patients, as well as parents, are misleading, one should have to contact a genetic counselor for proper guidance.
A genetic counselor can explain to you the situation and what to do next. Although I am not a professional genetic counselor, still as a geneticist I can give some suggestions to parents that will definitely help them to manage the situation.
First of all, don’t be panic if your pregnancy is diagnosed with Patau syndrome or trisomy 13.
Do not take any decision in a rush, immediately contact the genetic counselor near you.
The recurrent risk associated with trisomy 13 is very less, so the chance of your second pregnancy being affected by Patau syndrome is very less.
As I said in the previous article, the event occurs totally randomly, none of the parents is responsible for it so do not blame each other for that.
Instead of that, understand the situation and behave accordingly, try to support your partner.
Yes, it is an emotional trauma for the mother, think positive, this can happen to anyone.
If your doctor advises you for abortion, think about it, don’t be so emotional, ultimately your family has to face mental, social and economical problems.
If there is a 10% chance that your baby may live, you should go for it but remember, you have to face so many problems, in addition to this, your baby has to face problems too.
Also, living with the present condition can impact the daily lives of a parent, one of the parents should always take care of the baby. So keep these points in mind and make your decision accordingly.
Trisomies are commonly found, though trisomy 13 or Patau syndrome isn’t much common, it’s a problematic condition. The mortality rate is very high having serious developmental complications. The condition can be diagnosed early, but can’t be cured or managed. So it is advisable to discontinue the pregnancy.
Conclusively, trisomy 13 is a non-inherited genetic (more precisely) chromosomal aberration that causes serious health problems. Prenatal diagnosis is the only way to prevent Patau syndrome, to date, no medications or treatment for trisomy 13 are available.
Witters G, Van Robays J, Willekes C, et al. Trisomy 13, 18, 21, Triploidy and Turner syndrome: the 5T’s. Look at the hands. Facts Views Vis Obgyn. 2011;3(1):15–21.