25-Year-Old with Dwarfism Holds 2 Twin World Records with Identical Sister Who Is Over a Foot Taller

Growing up, Sierra Bernal was captivated by Guinness World Records.

“I would always read records and be like, ‘Oh, these are so cool,’ ” the 25-year-old aspiring singer and songwriter tells PEOPLE. “But I never really thought that I would actually ever have one.”

Well, as it turns out, she doesn't have just one, she was two.

Sierra and her identical twin sister Sienna set the record for rarest type of discordant twinning and sharing the greatest height differential between living identical twins — and they're both featured in this year's special edition to celebrate the 70th anniversary of Guinness World Records.

Sienna, or “Sinny,” was born with a form of primordial dwarfism that is so uncommon it has yet to be formally classified, according to the record keeping organization. Sinny stands at 4 feet, 4 inches, while her sister is 5 feet, 7 inches, giving them a height differential of over a foot.