Science in the News Trisomy 16

Jiwoo Kim

Mr.Youell

6/10/2014

Science Ext.

Trisomy 16

I have been researching on a chromosomal disorder called trisomy 16 and found this very interesting story of an individual with trisomy 16.

Shayna Marissa

Figure 1 Shayna Marissa at age 8

18 weeks into pregnancy, a baby girl was diagnosed mosaic trisomy 16. The mother was recommended termination and was informed by doctors that even if the baby survived the utero term, she could die shortly after birth or be terribly handicapped. The mother decided to give birth to the baby and Shayna Marissa was born on Valentine’s Day 1996 after 29 weeks of pregnancy, weighing only 700 grams.

Shayna did extremely well in elementary school for a girl who was discarded by doctors before she was even born. She was above average in every subject except for math in which she scored average. She was just like a typical elementary school girl who enjoyed gymnastics and hip hop like in Figure 1.

Figure 2 Shayna Marissa at age 18

In her teenage years, Shayna’s grades improved and she caught up with peers in height after puberty, reaching 164cm. She continued to be  positive and bright like in Figure 2. At the age of 18, Shayna proved the doctors completely wrong by graduating High School with 3.2 GPA, being accepted by an extremely selective college, and also receiving a $20000 for leadership scholarship!

So what is trisomy 16? According to two reliable sources I found,

                                 Source 1                                                                   Source 2 

a trisomy is a chromosomal disorder caused by nondisjunction during Meiosis (cell division for producing gametes) allowing an individual to have one extra copy of a specific chromosome, in this case (trisomy 16), the 16^th chromosome. Of all trisomies, trisomy 16 appears to be the most common in humans, appearing in 1% of all pregnancies.

Types of trisomy 16 include full trisomy 16, and mosaic trisomy 16. Full trisomy 16 is incompatible with life and nearly all affected fetus is miscarried in the first trimester. Another possibility is mosaic trisomy 16 meaning an extra 16^th chromosome is present in only some cells, which is an extremely rare condition. The mosaic trisomy 16 can be confined to the placenta so the baby can be completely normal while the placental cells are affected.

Figure 3 Amniocentesis & CVS diagram

The disorder can be diagnosed through CVS (Chorionic Villus Sampling) or  amniocentesis during pregnancy (refer to Figure 3) or by chromosomal testing after the loss.

CVS (Chorionic Villus Sampling) – A prenatal test which involves taking a sample from Chorionic villus which is a part of the placenta during the first trimester of pregnancy.

Amniocentesis – An accurate prenatal testing that involves taking a sample of the amniotic fluid during the second trimester of pregnancy. 

There isn’t sufficient data on the symptoms of either condition but it seems that affected survivors usually don’t suffer serious complications, like Shayna Marissa. Available research suggests that there is higher risk of preterm birth and intrauterine growth restriction meaning poor growth of the fetus during pregnancy. However, beyond pregnancy, some babies appear normal while others can have a set of health issues depending on the degree of mosaicism.