Patau Syndrome (Trisomy 13 )

 What Is Trisomy 13 or Patau Syndrome?

A baby’s genetic makeup is determined when the sperm meets the egg during fertilization. Typically, a full set of DNA is formed, which contains 23 pairs of chromosomes. Sometimes, extra chromosomes are shared, resulting in what is called a trisomy.

Patau syndrome is also known as trisomy 13. It means that a person has an extra copy of chromosome number 13.

What is trisomy 13?

Trisomy 13 is a rare genetic disorder that affects around 1 in every 7,409 births in the United States. It is present when there are three copies of chromosome 13 instead of the usual two in each cell in the body.

While rare, trisomy 13 is a very serious condition that can cause developmental issues that may lead to miscarriage, stillbirth, or infant death soon after birth.

A child who does survive may have a low birth weight and other serious medical issues.

Variations

If there is a complete extra copy of chromosome number 13 in each cell, the condition is called trisomy 13.

Sometimes this extra genetic information gets split between chromosome 13 and another chromosome — a translocation. This happens about 10 percent of the time.

In about 5 percent of individuals with trisomy 13, the extra copy of chromosome 13 only affects some cells and not all. When this happens, it’s called trisomy 13 mosaicism or partial trisomy 13. For individuals with mosaic trisomy 13, the signs and symptoms are generally less severe, and children may live longer.

What are the symptoms of trisomy 13?

You may have no symptoms during your pregnancy that indicate your child has Patau syndrome. Your doctor may uncover the first signs after cell-free DNA screening, other prenatal screening tests, or during a routine ultrasound exam.

Once your baby is born, you may observe the following features:

· low birth weight, problems with feeding, and low muscle tone

· microcephaly (small head) and face/head issues, like skin missing on the scalp, ear malformation, or capillary hemangiomas (raised birthmarks)

· microphthalmia (small eyes), anophthalmia (missing one or both eyes), or hypotelorism (eyes spaced closely together)

· cleft lip and palate

· polydactyly (extra fingers or toes)

· small penis or enlarged clitoris

· seizures

· apnea

· deafness

Around 80 percent of babies born with trisomy 13 also have congenital heart abnormalities. Some may also have conditions that affect brain development and the kidneys.

What causes trisomy 13?

In most cases, trisomy 13 happens spontaneously soon after the sperm and egg meet. The issue may arise as the reproductive material of either parent divides, or it may happen as cells divide after fertilization itself. In either of these cases, the extra chromosome happens at random.

That said, in rare cases, some people may pass a trisomy onto their child if they themselves have what is called a “balanced” translocation. This means that the parent carrier has a set of chromosomes that aren’t the norm but that they are balanced, so they don’t cause medical issues. However, when the parent with the balanced translocation has a child, the genetic information may be passed on and cause a trisomy 13 in the child.

How is trisomy 13 diagnosed?

Trisomy 13 can be diagnosed while you are pregnant or after your baby is born.

· A cell-free DNA screening is a noninvasive blood test that can be done as early as 10 weeks into pregnancy. If your screen shows a positive result, it means that your child may have trisomy 13, but that more concrete testing is needed.

· An ultrasound scan may reveal certain features that match up with Patau syndrome, like extra fingers or toes, small head size, or eye abnormalities.

· Amniocentesis is a diagnostic test that can be done after week 15 of pregnancy. Your doctor will obtain a sample of amniotic fluid to look for additional chromosomes.

· Chorionic villus sampling is a test that can be done earlier than amniocentesis, at 10 to 13 weeks. Your doctor will obtain a sample of placental tissue to look for additional chromosomes.

After birth, your child’s doctor may make a diagnosis based on a physical exam, certain characteristics, and blood tests to analyze chromosomes.

What is the treatment for trisomy 13?

Treatment for Patau syndrome is often targeted at whatever symptoms a child is experiencing. Instead of curative treatments, medical help tends to be focused on making the child comfortable, since many babies do not live long after birth.

Your doctor may assemble a healthcare team to provide care for various health conditions while working together. Treatments may eventually involve surgery — for heart issues, cleft palate or lip, or other conditions — physical therapy, and other medical or social services.

Children who live longer may also benefit from early intervention and special education programs as they grow.

What are the risk factors for trisomy 13?

Since most cases of Patau syndrome happen at random, it’s possible to have a child with this condition even if you have no known risk factors.

The primary risk factor mentioned in the medical literature is paternal age. So, as a parent’s age goes up, so does the potential for trisomy 13.

Again, the other risk factor is if either parent has a “balanced” translocation. This can be uncovered through genetic testing.

Your doctor may also suggest genetic testing if you already have a child with trisomy 13 (or another genetic condition) to determine if there’s an inherited factor at play that may impact future pregnancies.

What is the outlook for people with trisomy 13?

Trisomy 13 is a very serious but very rare condition. About half  of all pregnancies involving trisomy 13 will result in pregnancy loss before the 12th week. According to a 2017 study, 84 percent of pregnancies involving trisomy 13 that reach 39 weeks result in a live birth.

However, more than 90 percent of infants with trisomy 13 will not survive their first year. Most babies with this rare condition live only 7 to 10 days.

Around 5 percent of children with trisomy 13 will live beyond the first year, though they will likely have growth and developmental delays.

Some children with trisomy 13 may live longer, but this is extremely rare.