Trisomy is a chromosomal disorder when the affected individual has an additional chromosome, i.e, 47 chromosomes instead of 46. This abnormality is caused by the improper egg maturation and occurs spontaneously during conception. The random errors during cell division seriously impact the future development of the unborn baby with health problems ranging from mild intellectual and developmental disabilities to severe physical and cognitive problems. One of the major risk factors of trisomy is the maternal age as women in their late 30s and 40s are more likely to have infants with trisomy. One of the well-known types is trisomy 21, also known as Down syndrome. The less frequent types are Edward syndrome (trisomy 18), and Patau syndrome (trisomy 13). However, a trisomy can be detected during prenatal diagnostic testing but could also be identified after the birth of the baby with a blood test. The prenatal tests used to detect trisomy disorders can include ultrasound scans, maternal serum screening, amniocentesis, non-invasive prenatal testing (NIPT) and chorionic villi sampling. Some of the indications of trisomy disorders during pregnancy include;
- Excess amniotic fluid enveloping the infant
- The baby appears to be small for its gestational age
- The baby is not as active as expected
- Only one umbilical cord artery is detected
- Congenital defects such as heart abnormalities can be identified during ultrasound scans
The Trisomy Awareness Month in March now involves many organizations who try to raise awareness about the cause, treatment of these genetic disorders and the challenges they pose to the families. For those interested in more information about National Trisomy Awareness month, please visit nichd.nih.gov. Alternative ways an individual could get involved in the awareness month is by reaching out to families having a child living with Trisomy Disorder and learning more about their life or by teaching others about the disorder.
Trisomy 21 – Down Syndrome
It is also known as Trisomy 21, as affected individuals have three copies of chromosome 21 instead of two. One of the most common trisomy is Down syndrome and according to the Centers for Disease Control and Prevention (CDC), Down syndrome occurs about 1 in 700 live births in the United States annually. There are three types of this disorder and the most common one is Standard Trisomy 21 when either the father’s sperm or the mother’s egg contains the extra chromosome. In the case of Mosaic Down Syndrome, the extra chromosome spontaneously occurs as the embryo develops. The Translocation Down Syndrome is inheritable and accounts for around 5% of the cases.
‘Because Down Syndrome is associated with mild to moderate intellectual disability, early intervention is essential to maximizing the potential of each child’, says Karen Leydiker, a board-certified genetic counselor in CHOC’s Metabolic Clinic.
Some of the features of Down syndrome include;
- Relatively short limbs
- Flattened face
- Small teeth
- Physical growth delays
- Language and Hearing deficits
- Mild to severe intellectual disability
- Outwardly slanted eyes
- Flat ears set low on the head
The NIH had launched DS-Connect, a Down Syndrome Registry which is a powerful resource to facilitate information sharing among people with Down Syndrome, their family members, researchers and support groups. It also helps support recruitment for clinical studies on Down syndrome and interested individuals can contact the researchers about participating. For more details about DS-Connect, click here.
Trisomy 18 (Edwards Syndrome)
This is caused by the error in cell division, known as meiotic disjunction, which can disrupt the normal development of the infant in significant ways. The prevalence is estimated to be about 1 out of every 2,500 pregnancies in the United States and 1 in 6,000 live births. Unlike Down syndrome, Trisomy 18 presents more medical complications that can be life-threatening in the early years of their life. It is estimated that around 50% of the infants carried to full term will be born alive although baby boys will experience higher mortality rates.
Some of the common problems associated with Trisomy 18 include;
- Heart defects
- Kidney problems
- Severe developmental delays
- Esophagus not connected to the stomach
- Pocket of fluid on the brain
- Small head (microcephaly)
- Delayed growth
For those interested in getting the latest news and updates about Trisomy 18, to get involved or to connect with other families, visit Trisomy18 Foundation.
Trisomy 13 (Patau syndrome)
This is a rare genetic disorder that is estimated to affect around 1 in every 5,000 births and occurs because of an additional copy of chromosome 13 in some or all of the cells in the body. It severely disrupts the normal development of the baby who continues to grow slowly in the womb, have a low birth weight and about 80% of them will be born with severe heart defects. Often, the brain does not divide into two halves in a condition known as holoprosencephaly which can result in features such as cleft lip and palate, absence of one or both the eyes, problems with the development of the nasal passages and abnormally small eyes. Additional problems can include;
- Severe Intellectual disability
- Skin missing from the scalp
- Ear malformations
- Small head (microcephaly)
- Abnormal cysts in the kidneys
- Abdominal wall defect
- Abnormally small penis in boys and enlarged clitoris in girls
Because of various life-threatening medical problems, these infants tend to die within their initial days or weeks of life and only around 10% of them continue to live past their first year. However, around 5 to 10% of babies with the less severe forms of the syndrome could continue to live for more than a year.
Couples expecting a baby with a genetic problem could benefit from meeting genetic counselors which is not only limited to parents but also open to family and friends who may have questions or need to learn more about the condition. Genetic counseling could also involve a discussion about genetic tests, information about relevant patient support groups and advice if your child is affected by an inherited condition or if the couple wants to have another child.