Their son's first birthday was a welcome cause for celebration for the family of a Florida baby born without a large part of his head and skull. Little Jaxon Buell wasn't expected to survive more than a few days after he was born last year.

On Facebook, more than 100,000 people now follow the boy's remarkable survival story and the hashtag #JaxonStrong.

Doctors discovered something wrong in the baby's head shape during a routine ultrasound when mom-to-be Brittany was pregnant, but they didn't know the exact cause. After Jaxon was born, Brittany and Brandon Buell were told he had a birth defect called anencephaly that occurs when the beginnings of the nervous system form incorrectly early on in the pregnancy. Most babies with the rare condition cannot survive long past birth.

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"Every doctor we've talked to is fascinated that Jaxon is here today, and they can no longer predict a prognosis," Brandon Buell wrote in a Facebook post. "We know the reality behind this better than anyone else, what Jaxon is up against, and that his life is already miraculous at this point."

Amazingly, Jaxon is marking many infant milestones: "He is talking up a storm these days, truly teaching himself how to communicate with us in his own way ... He is so normal in so many ways. He is a baby who is dealing with teething, he cries when he's hungry, he hurts from gas pains, he throws ups, he cries, he poops, he sleeps, he repeats."

But over the past few months, seizures, feeding complications and close calls prompted the couple to seek a second opinion, hoping they might find more treatments options to help Jaxon, the couple told The Boston Globe. They flew to Boston and went to the emergency room at Boston Children's Hospital where they were given a more specific diagnosis of microhydranencephaly.

"It's really helpful to finally have a diagnosis that makes sense," Brandon told The Boston Globe. "We came to Boston hoping to find a way to add something to the quality and comfort of his life."

Brandon Buell via Facebook

About 1 in 4,859 babies are born with anencephaly each year in the U.S., according to the CDC, and most live very short lives. Microhydranencephaly -- the combination of a small head and malformed brain along with an absence of brain hemispheres that are replaced by fluid-filled sacks -- is even more rare and untracked.

Brandon Buell added that he believes many people will be positively influenced by learning more about his son's condition and expressed hope that he would be one of the children that makes it to adulthood after he gets through the challenging first year. The family's GoFundMe page exceeded the goal of raising $70,000 for the next year to fund Jaxon's treatment and care.

The disorder has no known cure because the basic structures of the largest part of the brain responsible for complex thought and communication, the cerebral cortex, are not present.

The couple have posted pictures and videos of Jaxon learning new skills like sitting up and reaching, and they say he can call his parents by name: "Mama" and "Ah Ah" (Dadda), and "Addy" (Daddy).

"Jaxon's tiny footprints will have a lasting impression on this world, and that he has already touched and inspired more lives in one year than most of us ever will in our lifetime," Brandon Buell wrote on Facebook. "For his life, I am better, I am blessed, I am grateful, and I am quite simply, one proud 'Addy.'"