Little clumps of cells turn into tiny bodies than those infants grow into chunky toddlers, and those toddlers eventually hit puberty and become adults.

Start at the end of the 20th century, doctors were mystified by one American girl who essentially remained a toddler until her death at age 20.

She would become famous in medical circles as the first documented case of a condition we now call nio te Nick complex syndrome, or NCs, for short, a rare disease where infants just don't grow up.

And while scientists still don't really know how this mysterious condition happens, further research into it can help us better understand human development.

When the girl was born in 1993 she had multiple physical anomalies.

Both of her hips were dislocated, for example, and she had some breathing and gut issues, her doctor presumed.

These body person form is expected in utero because of large scale Genetic mutations like chunks of her chromosomes had been rearranged, but according to tests, her chromosomes were typical.

That was the first sign that something was strange about her case and things only got more puzzling from there as the years went by.

This young girl just I didn't grow up.

At her death at age 20 she still had the height, weight and facial features of a toddler.

Also, her brain hadn't developed past the toddler stage, and she never hit puberty.

Certain aspects of her had aged, though.

When she was 16 for example, she had some adult teeth, but not all of them.

More like what you'd expect of an eight year old and her bones had begun developing into adult bones but hadn't finished this.

Research, published in 2009 also looked at her telomeres, little caps on the tips of chromosomes that shorten as you get older.

They were the link normally seen in someone older, but that could have been a side effect of her body.

Staying infant like so.

There was nothing about them that indicated developmental delays.

In the end, doctors were unable to figure out what was causing her knee Ott me or child like appearance.

But her seemingly unique condition led to a lot of media attention, and as her story spread, more parents came forward with stories of kids seemingly stuck in toddlerhood.

Thanks to this, doctors were able to find five similar cases for a 2015 study.

Just like with the first girl, none of the participants showed anything out of the ordinary and genetic tests for known conditions.

Theo only big thing, they found was that the age of their blood cells lined up with their actual age.

So these patients seem to be aging but not developing.

Unfortunately, the results didn't really shed light on why so scientists were still stumped.

Determined to get to the bottom of this mystery, researchers individually sequenced each and every participants entire genome, thinking that there had to be some clues hidden somewhere.

And finally, they did find something as detailed in a study published in 2018 5 of the six participants had never before seen mutations in five potentially relevant genes.

They weren't exactly a smoking gun, but they provided some intriguing clues about the ultimate cause of the syndrome, like some of these mutations were in jeans that seemed to be pretty important in development because they're associated with other developmental disorders.

But what was truly revealing was that most of these mutated genes were involved in one way or another with regulating transcription.

That's the process.

Where DNA is red to make are in a an important step in turning genetic blueprints into protein, this point of the team back to something they suspected years ago epigenetic See at any given moment on Lee, some genes are actively being transcribed and turned into proteins what geneticists refer to as being expressed.

The gene expression can differ from person to person or even in the same parts of the same person at different times in their life, because modifications to all sorts of cellular machinery can influence how a DNA sequence is red.

So even if a gene sequence is unchanged, mutations toe other parts of the genome can affect the amount of protein that's produced from that gene, or even the protein's shape or function.

Since many genes contain information for more than one form of a particular protein, and that's what all the genes with mutations in the N.

C s patients have in common, they're all involved in some way and the processes that govern gene expression specifically, many of the genes play a part in modifying, hissed owns proteins which help our long strands of DNA bundle up into compact package is, and how a particular section of DNA is packaged can influence whether or not the jeans and get transcribed.

Even still, the researchers don't think these expression influencing mutations are enough to explain NCs all by themselves.

There seems to be something scientists are missing, whether it's other mutations, environmental factors or something they haven't thought of yet.

And figuring it all out will ultimately depend on finding more people to study as spotting things like epigenetic changes generally requires a fairly large sample size, with the condition this rare that will take time.

So that's where things are at right now.

Scientists have put over a decade of research into neon nick complex syndrome and still don't know exactly what causes it.

But they're pretty sure it comes down to how different genes end up being expressed.

Now the challenge is to figure out precisely which genes are being turned on and off.

How and why.

These changes prevent these infants from growing up.

Figuring all that out will reveal a lot about development that we don't currently understand.

And it might even point toward treatments for N.

C S and other developmental disorders.

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