What is Trisomy 13?
Trisomy 13 is a condition resulting from an extra copy of chromosome 13, first identified by a researcher named Patau and his colleagues in 1960. It’s a rare condition that happens in 1 out of 10,000 to 20,000 live births, but unfortunately, over 95% of pregnancies with Trisomy 13 result in fetal death.
Trisomy 13 can show up in three ways: complete, partial, or mosaic. In complete trisomy 13, occurring in about 80% of cases, there are three copies of chromosome 13 in every cell. Partial trisomy 13 happens when a specific cell-transformation event occurs, causing parts of chromosome 13 to break off and attach to another chromosome. Mosaicism, which makes up only 5% of cases, is when some cells have an extra chromosome 13, while others have the normal amount.
This condition usually happens when parent cells don’t divide correctly during the process that forms eggs and sperm. This error is mostly linked to the mother’s cells and tends to happen more frequently as the mother’s age at conception increases. About 91% of trisomy 13 cases result from this maternal age-effect. As for the remaining cases, these can be inherited from parents who carry a balanced form of the condition. This happens when a piece of chromosome 13 is attached to another chromosome, but the person has the right amount of genetic material.
Babies born with trisomy 13 typically have several birth defects and intellectual disabilities that can make survival difficult. These children often have physical abnormalities that develop because certain cells important for body formation don’t merge correctly. These abnormalities may include problems related to genes known as SHH. Despite the high rate of early death for those with trisomy 13, this condition is still important from a medical perspective because the symptoms can vary, particularly in children with the mosaic form of the disorder.
What Causes Trisomy 13?
Trisomy 13 is a condition where a person has three copies of the 13th chromosome instead of the normal two. This usually happens because of a process called ‘nondisjunction’ which means the chromosomes don’t separate properly during the creation of reproductive cells. Most instances of this condition, about 91% of cases, happen because of a mistake during this process in the mother. This mistake tends to happen more often in mothers who are older than 35 years old.
Sometimes, a different version of trisomy 13 can occur, resulting in fewer physical and mental challenges. This is caused by a ‘translocation’, where parts of certain chromosomes (usually 13 and 14) break and reattach wrongly. The effects of this chromosome rearrangement depend on how balanced the changes are; a balanced translocation usually results in a milder form of the disorder, while an unbalanced translocation, which alters the amount of genetic material in the chromosomes, causes more severe symptoms.
Another form of trisomy 13 is ‘mosaicism’, where the person’s cells have different sets of chromosomes. Some cells have the normal pair of chromosome 13s, while others have an extra one. This leads to a wide range of symptoms, as different cells in the body are affected differently. Interestingly, those with this condition often show less intellectual disability.
Risk Factors and Frequency for Trisomy 13
Trisomy 13 is a condition that ranks third in terms of frequency, happening in about one in 10,000 to 20,000 live births. Most of the deaths linked to Trisomy 13 happen before birth, with around 6 to 12% of almost newborns surviving past their first year. In developed countries, about 90% of Trisomy 13 cases are diagnosed before birth. Heart and nervous system abnormalities are some of the most common issues associated with Trisomy 13.
- Trisomy 13 happens in 1 out of every 10,000 to 20,000 live births, making it the third most common trisomy.
- The majority of deaths from Trisomy 13 occur before birth.
- The survival rate past the first year of life is only 6 to 12%.
- In developed countries, about 90% cases are diagnosed before birth.
- Common health issues in individuals with Trisomy 13 include heart and nervous system abnormalities.
Signs and Symptoms of Trisomy 13
Trisomy 13 is a condition that typically presents with quite a few findings. These can include:
- Abnormal brain development, known as holoprosencephaly
- A brain malformation called Dandy-Walker
- Missing skin, referred to as aplasia cutis
- A combination of a cleft lip and palate
- Extra fingers or toes, known as postaxial polydactyly
- Born with a heart disease
- Polycystic kidney disease
- Issues with the urinary and reproductive system
- Abnormal development or function of the female reproductive system, called gynecological dysgenesis
- Persistent low blood sugar due to the overproduction of insulin, referred to as hyperinsulinism
Many of these symptoms can be detected while the baby is still in the womb, where the most common finding is related to delayed growth.
Testing for Trisomy 13
The initial check for a condition called trisomy 13 often starts with a special scan done between the 11th to the 14th week of pregnancy. This is known as fetal nuchal translucency (FNT), which measures the fluid area at the back of the baby’s neck. For babies with certain conditions like trisomy 13, this area is often larger, measuring 3.5mm or more.
During the first trimester of pregnancy, doctors also measure the levels of two specific substances in the mother’s blood: free beta subunit or total human chorionic gonadotropin (B-hCG) and pregnancy-associated plasma protein-A (PAPP-A). In cases of trisomy 13, both of these substances are typically found in lower amounts. However, this pattern is not unique to trisomy 13 and can be seen in another condition called trisomy 18 as well.
Another way to screen for trisomy 13 is through non-invasive prenatal testing (NIPT) which uses fragments of the baby’s DNA present in the mother’s blood. However, due to cost considerations, invasive testing methods are sometimes preferred. These include chorionic villus sampling (CVS), a test that collects a small sample of the placenta for testing and can be done between the 11th and 13th week of pregnancy. Another method is amniocentesis, a test that collects a sample of the amniotic fluid surrounding the baby for testing and is usually done between the 15th and 18th week of pregnancy.
It’s crucial to note that a high mortality rate is associated with trisomy 13 and 18 due to the termination of pregnancies with a confirmed diagnosis. The final confirmation of trisomy 13 can only be established after the baby is born, through techniques like karyotype testing (a snapshot of all the chromosomes inside the baby’s cells) and fluorescence in situ hybridization (FISH), a procedure used to visualize specific genes or regions of genes.
Treatment Options for Trisomy 13
In the past, it was commonly believed that having multiple organ dysfunctions as a result of trisomy 13 and 18, genetic disorders that cause an extra chromosome, meant that the individual would not be able to survive. However, some exceptions have been observed, making it a morally complex area.
Nowadays, the focus is on fostering open communication between doctors and parents. This allows the parents to be fully informed about their child’s quality of life and treatment options related to their specific genetic abnormalities. While surgical methods do exist to address many of the serious abnormalities associated with trisomy 13, the ten-year survival rate after such intervention isn’t promising, standing at only 12.9%.
What else can Trisomy 13 be?
When trying to diagnose trisomy 13, it’s important that doctors also consider conditions that might have similar early symptoms. These include:
- Edwards syndrome, due to similarities seen during early pregnancy screening
- Partial duplication of chromosome segment 13q
- Pseudotrisomy 13, another genetic disorder
The use of modern, non-invasive medical technologies makes it easier to differentiate these conditions, which can often appear similar to trisomy 13 during prenatal checks.
What to expect with Trisomy 13
Research indicates that about half of newborns pass away within the first month, and up to 90% within the first year. Recently, thanks to information provided by support organizations like the Support Organization for Trisomy 13, 18, and related disorders (SOFT), doctors have been able to directly treat patients, as opposed to giving palliative care, which aims to relieve pain without treating the underlying cause.
These treatments have improved the survival rate of patients, but there’s a lack of research data to support the effectiveness of these aggressive treatments on the overall survival rate.
Possible Complications When Diagnosed with Trisomy 13
Trisomy 13 presents certain risks for both the mother and her unborn child, leading to a higher risk of death for both. Research indicates that carrying a child with trisomy 13 may lead to a higher chance of the mother developing preeclampsia, a potentially dangerous pregnancy complication related to high blood pressure, and giving birth early.
However, the baby’s mortality risk is linked to other critical health conditions. These include:
- Central sleep apnea: a condition where breathing regularly stops and starts during sleep
- Critical heart structure issues
- Pulmonary hypertension: high blood pressure within the arteries of the lungs
- Aspiration: a condition where the baby breathes in food, stomach acid, or saliva into their lungs
- Obstructions in the upper respiratory tract: blockages in the airways that can make breathing difficult
Preventing Trisomy 13
It’s beneficial to have a team of diverse medical professionals involved during the prenatal period to enhance both the health of the expecting mother and the survival chances of the baby. This team could include an obstetrician (a doctor who specializes in pregnancy and childbirth), a fetal concerns center nurse (a nurse focused on monitoring unborn babies), a genetic counselor (a healthcare professional skilled in understanding genetic conditions), a neonatologist (a doctor who cares for critically ill newborns), and a social worker.
Part of the team’s job is to ensure the patient fully understands various aspects related to the pregnancy. This might involve explaining how certain diseases are passed from parents to child, discussing the potential risks if the mother decides to continue the pregnancy, and emphasizing the benefits of after-birth care for the baby’s well-being.
