Trisomy 13, also known as Patau Syndrome, is a chromosomal abnormality where an individual has an extra chromosome 13. Trisomy 13 was first recognized by Patau and his colleagues in 1960 (Matthews, 1999). It affects approximately 1 in 12,000 births and is the least common of the trisomy syndromes, after trisomy 18 and trisomy 21 (Down syndrome). An abnormality of the chromosome occurs when mitosis or meiosis does not happen correctly. During mitosis, when the cells are dividing, chromosomes are either lost or gained. The chromosomes do not separate evenly. When the distribution of chromosomes during cell division occurs after the egg is fertilized by the sperm, mosaicism occurs. The fetus will have 47 chromosomes in some cells and 46 chromosomes on other cells.
There are three variations of trisomy 13; full trisomy 13, which is the presence of an extra chromosome 13 in all cells, trisomy 13 mosaicism, which is the presence of an extra chromosome 13 in some of the cells, and partial trisomy 13, which is the presence of a part of an extra chromosome 13. The chromosomal abnormality usually begins with the egg cell, therefore there are more female fetuses affected with trisomy 13 than males. Women over the age of thirty-five are at greater risk of having a child with trisomy 13 (Genetics.edu, 2007). Roughly one out of 3-4 eggs fertilized are considered to have a chromosomal abnormality, but our bodies usually react with a miscarriage.
There are several ways that trisomy 13 can be detected during pregnancy such as: ultrasound, amniocentesis, or maternal serum screening. While these tests can pick up on the genetic likelihood that the fetus will have a trisomy defect, many parents chose not to get this testing done. The severity of the symptoms associated with trisomy 13 depends on the portion of the chromosome that is affected, as well as the percentage of cells that have an abnormality. If an infant presents with mosaic trisomy 13, the symptoms will be less severe than if the infant has trisomy 13 in all the cells of their body.
The timing of division, the cell lines, or the tissues that are affected, determines which type of trisomy the infant will have. Some of the manifestations of trisomy 13 can often be mistaken for other congenital birth defects. Some of the general defects associated with trisomy 13 are: brain, facial, hear, renal, and limb abnormalities. One of the major defects that occur is Holoprosencephaly, which occurs in more than 60% of fetuses (Matthews, 1999). Holoprosencephaly is a cephalic disorder where the brain does not divide into two hemispheres. Infants born with trisomy 13 often have severe mental retardation, cleft lip and palate, small eyes, low set ears, craniofacial abnormalities, renal abnormalities, and extra digits.
Survival rates for children born with trisomy 13 are very low. The majority of infants born with trisomy 13 will die within the first few days of life, 50% will die within the first month, and a small percentage will survive to one year (Genetics.edu, 2007). Children with mosaic trisomy 13 may live longer, but will have marked developmental delays and growth. The small percentage of children that do live with partial trisomy 13 will function in the severe-to-profound developmentally handicapped range (IQ/DQ<40), but may achieve many normal childhood skills and age appropriate learning (Matthews, 1999).
At birth, complications begin almost immediately. Infants usually have low birth weight, difficulty feeding, decreased muscle tone, and heart failure. Comfort care usually begins at this time. Counseling and preparations are made for the families to help cope with the decisions that come with having a child with trisomy 13. There is no cure for trisomy 13 and in most cases, is not inherited. If the infant is born with partial trisomy 13, then surgical intervention, therapies, and life-saving measures need to be decided at that time. Since the prognosis is generally not good, the decision to prolong life must be taken into consideration. It is important after the birth to confirm the suspected chromosomal abnormality. If the results show that there has been a translocation of the chromosome, then genetic counseling and recurrence rates need to be discussed with the family. Prenatally, a genetic test can be done on an embryo that has been created via in vitro, to prevent this defect from occurring again.
A.D.A.M. Medical Encyclopedia (2011). Retrieved from http://www.ncbi.nlm.nih.gov
The Australian Genetics Resource Book(2007). Retrieved from http://www.genetics.edu.au
Matthews, AL. (1999). Chromosomal abnormalities: Trisomy 18, Trisomy 13, Deletions, and Microdeletions. The Journal of Perinatal Neonatal Nursing, September 1999.
MLO: Medical Laboratory Observer (2012). Vol. 44 (3): 6 ISSN: 0580-7247. Retrieved from http://www.mlo-online.com
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