The chance of being born with an identical twin is pretty rare, but the chance of one of the twins being born with primordial dwarfism is practically unheard of.
You may be familiar with the most common types of twins - fraternal and identical - but have you ever heard of discordant twins?
Twenty-three-year-old sisters Sienna Bernal and Sierra Bernal of Tomball, Texas, USA, are identical twins who hold the record title for the rarest form of discordant twinning.
Twin growth discordance is a term used in obstetric imaging to describe a significant size or weight difference between the two foetuses of a twin pregnancy.
To be classified as a growth discordance, the estimated foetal weight of the smaller twin must fall under the 10th percentile.
Sierra weighs 98 Ibs (44.4 kg) and stands at 5 feet 7 inches (170 cm), while Sienna weighs 50 Ibs (22.6 kg) and measures 4 feet 4 inches (132 cm).
With a height discrepancy of over a foot and a weight difference of 48 pounds (21.7 kg), the discordance between the sisters is evident.
Sienna "Sinny" and Sierra are the only known identical twins with this difference, making Sienna the first twin with primordial dwarfism.
When Sienna was born, she was nearly six weeks behind her sister in development.
"Sierra weighed 4 Ibs 4.8 oz (1.95 kg) and Sienna weighed 1 Ib 7 oz (0.65 kg)," said their mother, Chrissy Bernal.
"Sienna stayed in the NICU for 108 days and then she went into the hospital a lot over the next several years of her life, off and on for three to six weeks at a time."
Chrissy recalls first receiving the surprising news she was carrying twins, just six weeks before they were born.
"They [the doctors] said ‘So, you’re having twins, but you need to quickly get over that because we need to talk about baby B’," said Chrissy.
"So, I had to absorb that information really quickly and then just move straight on to her [Sienna] being so small."
Chrissy said doctors knew Sienna had Dandy-Walker Syndrome before she was born because they could see that she was missing a portion of her brain and noticed she was much smaller than "twin A" but didn’t know why.
"Dwarfism wasn’t something they were thinking was a possibility, I guess because she was still proportionate," said Chrissy.
"Most forms of dwarfism are not proportionate like Sienna’s type is."
In fact, Chrissy says she had to put up quite the fight to find out what kind of dwarfism Sienna had.
"They kept saying it was failure to thrive, which is just a generic term they use when they’re not sure what’s going on," she said.
Doctors assumed a hole in Sienna’s heart or the fact that she kept getting pneumonia were potential reasons behind her small size.
At one point, Sienna was even intubated with a feeding tube because it was thought she wasn’t receiving adequate nutrition.
"It wasn’t until she was about six that we discovered she had dwarfism," said Chrissy.
"It was a visiting geneticist from Belgium who walked in and goes 'Oh, I know what she has. Here are the tests you need to run and that will confirm it'."
Sure enough, Sienna was found to have primordial dwarfism, which is a form of dwarfism that results in a smaller body size and other growth abnormalities.
"There are fewer than 200 people in the world diagnosed with primordial dwarfism and Sienna’s type is one that’s unknown," said Chrissy.
"Actually a few of our friends who have primordial dwarfism are in the Guinness [sic] book so it’s kind of cool that they’re [Sierra and Sienna] in there too."
Chrissy refers to her daughters as "monozygotic twins", adding that the word "identical" is misleading because identical twins don’t always look like one another.
Monozygotic twins result from the fertilisation of a single egg, which then splits into two.
"Because Sienna’s diagnoses are mutations, her genes mutated after the egg split," explained Chrissy.
"That’s how they’re so different even though they’re ‘identical’ twins."
But despite their differences, the Bernal sisters have more in common than meets the eye.
"They’re both really, ridiculously silly and they are both very funny in their own right," said their stepfather, Joey Bernal.
"While Sierra can say things to be funny, Sienna will say things not even trying to be funny and that’s when you about die from laughing."
In fact, most of the time, the twin sisters don’t feel very different at all.
"I can’t recall noticing differences. We were born in the situation that we’re in, so we didn’t know anything else until we got older," said Sierra.
"I don’t think differences became as apparent until we got older, and I started driving."
In many ways, Sienna’s primordial dwarfism has been the catalyst for strengthening the twins’ sisterly bond.
"I think I’ve definitely been put in more of a 'big sister' role rather than a 'twin' role," said Sierra.
"With Sienna being my twin and having Dandy-Walker and primordial dwarfism, it has affected our relationship in the sense that we have to be very communicative, and we can’t be jealous of anything because we do have very different lives."
Instead of viewing growing up alongside her otherwise healthy identical twin as a hardship, Sienna has formed an unbreakable connection with Sierra in a way that only twins can.
"It was probably a lot more difficult for Sierra to have to take on that role, but I think at the same time too, if she hadn't have been there, I don't think that Sienna would have progressed to the degree that she has," said Joey.
"She always wanted to be more like her sister and she always worked harder to get to that level."
Sienna says her sister has always been her biggest source of support, and that she doesn’t know where she would be without her.
"She [Sierra] has helped me with my emotions more and helping me control them," said Sienna.
"When I was younger, my emotions would explode because I didn’t know how to control them, but as I’ve gotten older, I’ve learned how to control my anger."
But it isn’t just Sienna that has had a positive impact on her sister’s life.
Sierra, who is an aspiring country singer, says her twin hasn’t just shaped her outlook on the world, but her music as well.
"Having Sienna as my sister has made me grow up faster than I think I would have naturally," said Sierra.
"I think in a way it influenced my music because it made me perceive things a bit differently than I probably would have. In turn, my music is a bit different than it would have been."
Although Sienna and Sierra see their discordance as unique and don’t let their differences get in the way of their relationship, the two realise there will always be some additional difficulties brought on by Sienna’s condition.
Primordial dwarfism will sometimes cause added challenges like scoliosis, which affects Sienna and often causes a great deal of pain.
Additionally, her short stature means she must sometimes be a bit innovative or look to her taller sister for help with accessing anything too far out of reach.
Other times, its curious onlookers who remind the Bernal twins that a difference even exists in the first place.
"Sometimes when we go out in public, people will think she’s my mom and not my twin because I’m so short," joked Sienna.
"When we go to bars, people think I’m eight even though I’m 23. It’s really funny."
@sierra_bernal Answer @im_siowei Late 2020 count? #twins#identicaltwins♬ Cheers - New Rules
Despite their incredible uniqueness, Sienna wants the world to know that there are some positive aspects to being diverse.
"It’s not always bad being short. As I'm getting older, I'm like 'my clothes are cheaper, and my shoes are cheaper—when you can find them'," joked Sienna.
"Other than that, I live a normal life. I just have to be more creative."
Chrissy is incredibly proud of both of her daughters, but is especially impressed by Sienna's mental and emotional transformation, which she says has been nothing short of amazing since starting her jewelry business.
Additionally, Sienna dedicates her time to improving the lives of others born with dwarfism.
"It has also been rewarding to witness and work together as advocates for the Equal Restroom Access for Little People Movement," said Chrissy.
"It gives her a positive outlet to make incredible social changes to live her life, and others like her, more fully and independently."
Ultimately, Sienna and Sierra share a magical innate bond, which neither primordial dwarfism nor Dandy-Walker Syndrome can ever come between.
In the past, the sisters have lost the same exact teeth at the same time and would even sleep in the same positions.
"One time, one of them (twin A) fell asleep on the sofa in a particular position. I went upstairs to look for her sister and she (twin B) was in her room asleep in the same exact position," said Joey.
“By the time I come back down, this one (twin A) has already changed positions again, so I thought ‘What are the odds?’ and I went back up and sure enough, she (twin B) had changed positions as well.”
Chrissy and Joey enjoy witnessing the love shared between their daughters and admit that it has been a beautiful reality to be a part of.
"At the end of the day, they’re still tight," said Joey.
"They’re still each other’s twin and they treat each other as such."
Related Articles
