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A mom of 3 learned she had mosaic Down syndrome through genetic testing. Here's why she's 'happy' with the diagnosis.

A mom with mosaic Down syndrome chronicles her journey. (Photo: Getty Images)
A mom with mosaic Down syndrome chronicles her journey. (Photo: Getty Images)

For Ashley Zambelli, a surprise diagnosis allowed her to have an even more special bond with her children.

The Michigan-based mom, 23, recently found out she has Mosaic Down syndrome, a condition in which a person has some cells with extra chromosomes and some cells with the typical number. Yet Zambelli tells Yahoo Life that she would not have discovered her own condition if not for that of her children’s.

Testing for Down syndrome

In May of 2019, Zambelli miscarried at nine weeks gestation, needing an emergency dilation and curettage (D&C). She and Doyle had genetic testing done, and were told that the fetus had tested positive for trisomy 21, a type of Down syndrome, a condition in which individuals have an extra copy of a chromosome. Trisomy 21, one of the three types of Down syndrome, indicates that an individual has a duplicate of chromosome 21. The extra chromosome changes how one’s brain and body develop, and can lead to certain physical and mental challenges.

When Zambelli became pregnant again with the pair’s daughter Lillian, now 2, she chose to do genetic testing in utero; Lillian was diagnosed with trisomy 21 at 10 weeks gestation. One year later, their daughter Evelyn, now 15 months, was born, and though Evelyn also went through genetic testing, hers came back negative for trisomy 21.

When Zambelli, who is now seven months pregnant, learned she was expecting a third daughter, she and Doyle decided to have genetic testing done again — revealing that this child, like Lillian, has trisomy 21. Due to Zambelli’s history, her ob-gyn was “a little concerned.”

“She said, ‘This does not seem normal, this is now your third child with trisomy 21,’” Zambelli recalls. While the mom's karyotype test (used to determine the amount of chromosomes in one’s cell) and fluorescence in situ hybridization test (to check for genetic abnormalities) were “completely normal,” Zambelli’s geneticist was “really convinced” that she might have Mosaic Down syndrome.

“We did one more test, which was a buccal swab,” Zambelli explains. “That came back saying that 3% of my buccal cells were positive for the extra 21st chromosome. That’s how they diagnosed me, but it was still confusing, because they said ‘Well, this is only your buccal cells — there could be more distributed throughout the rest of your body.’ They estimate that 20% of my body has the extra chromosome, but they won’t know that until we do more genetic testing.”

Feeling empowered post-diagnosis

Zambelli’s diagnosis, while a surprise, ultimately made sense for the mom, who says she noticed certain things growing up that suggested she may have the condition, such as her more almond-shaped eyes and indicators of low muscle tone.

Also, she says, “For me as a child, I really lacked comprehension skills when it came to reading it — I had to reread a sentence three to five times."

Zambelli, who has shared her journey on TikTok, knows that she would have never been tested for mosaic Down syndrome had she not had kids with trisomy 21. In fact, even though she had a heart condition called Inappropriate Sinus Tachycardia (IST) — in which her heart has more than 100 beats per minute while at rest — genetic testing was never recommended.

“They always thought it was [connected to] Lupus, because my father has Lupus, and he’s been in remission for 20 years,” she explains. “They tested for Lupus, and nothing was matching up, and they just kind of stopped. It was like, ‘We’re not going to look any further. Your child is normal.’”

Now that she has been diagnosed, Zambelli feels more empowered about her health.

“I can go back to all of my doctors and tell them, 'Hey, I was just diagnosed with this, can we do further testing on my heart, get me into physical therapy for my muscle issues?' It opens a whole new door of taking care of myself now,” she explains.

Zambelli also feels a deeper connection between herself and her children. She says she notices some of the potential symptoms of her own mosaic Down syndrome in her daughter Evelyn, as well. Though Evelyn does not have trisomy 21, there is a possibility that, like her mom, she will also have mosaic Down syndrome, and is currently awaiting results from her own buccal swab.

“My kids have Down syndrome, so for me as a mom,” she explains, it's helpful, “because I know I can relate to them on a certain level.”

What to know about mosaic Down syndrome

Sonja Rasmussen, M.D., professor of genetic medicine at the Johns Hopkins University School of Medicine, explains how Down syndrome and mosaic Down syndrome differ.

“Typically, we all have 46 chromosomes,” she shares. “Chromosomes contain our genetic material, and we get 23 chromosomes in the egg from our mom and 23 chromosomes in the sperm from our dad. Chromosomes are numbered from 1 to 22, with the 23rd pair being the sex chromosomes.

“In the most common type of Down syndrome, there are 47 chromosomes, with the extra one being chromosome 21 — so the patient has three No. 21 chromosomes in all the cells of their body. In about 1 to 2% of persons of Down syndrome, mosaicism is seen — that is when some of the cells have 46 chromosomes (two No. 21 chromosomes) and some cells have 47 chromosomes (three No. 21 chromosomes).”

She says that while people with mosaic Down syndrome can have some of the typical features of Down syndrome, they can also me more mildly affected, sometimes to the point where, as with Zambelli, the diagnosis can be missed.

“The effects seen depend on the percentage of cells with the extra chromosome in the body and where those are — whether they are in the brain, muscle, heart or other tissues,” she says.

She adds that trisomy 21 is the most common type, and it occurs when one of the parents passes down two No. 21 chromosomes, rather than just one, giving the baby three No. 21s in all cells of the body.

“Mosaic Down syndrome is different — it occurs when there is error in cell division in development,” she notes. “After the egg and sperm come together, the cells make copies of chromosomes and make many copies of cells. In a person with mosaic Down syndrome, the error is something that can happen as those cells are multiplying. Then the person has some cells with extra chromosomes and some cells with the normal number.”

Dr. Rasmussen notes that it’s very possible that someone with mosaic Down syndrome will have no health issues at all, though they can also share many of the issues that one has with Down syndrome.

“The person could have some physical features of Down syndrome, such as the single crease often seen in the palm of a child with Down syndrome, or even health issues such as heart defects, hypothyroidism, low muscle tone and so on,” she adds. “It really depends on where the cells with the extra chromosome are located and the percentage of cells with the extra chromosome.”

As for Zambelli, the diagnosis meant a shift in perspective.

“Knowing that I have these certain characteristics, and knowing that my children will have these characteristics as well, it gives me a whole new perspective on bonding with them as they grow up," she says. "I know what to expect and how not to treat them, based on how I was treated, such as with school and socializing and … certain developmental delays. It helps me to be more patient with them.”

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