Thanks to Linode for supporting this  SciShow video!

For all things Linode,   you can go to linode.com/scishow. That  link gives you a $100 60-day credit on   a new Linode account. [♪ INTRO]  For those of you who are fans of diet soda, or  fans of reading ingredients labels, like me,   you may have noticed a warning that says “contains  phenylalanine” on every can, bottle, or jug of   diet soda you’ve ever had.

Maybe you spent two  seconds wondering about the dangers of this   mysterious five-syllable menace before shrugging  and getting on with your refreshing beverage.   And for 99.99% of you, that’s fine. But if you  happen to be one of the one in ten to fifteen   thousand people living with one rare genetic  disease, that information was so important   it’s worth baffling the rest of us over.  Phenylalanine is an amino acid. That is,   a basic, building-block compound the body strings  together to make proteins for a variety of uses.   Phenylalanine is also a precursor in creating  helpful substances like adrenaline and dopamine,   which play a variety of information-carrying  roles in our body.

In short, phenylalanine is   an essential ingredient in our body’s kitchen.  Though as vital as phenylalanine is to the body,   it can’t be produced by the body. Instead, we  get our phenylalanine fix from external sources,   mainly foods such as meat, poultry, fish, cottage  cheese, lentils, peanuts, and sesame seeds. That   makes it one of the so-called essential amino  acids, meaning essential to ingest in our diets.   The amino acid is also found in aspartame,  an artificial sweetener used in many of the   low-calorie, super-sweet foods and beverages  on the market today.

That includes many diet   soda brands, sugar-free chewing gum, and so  on. So, if it’s such a necessary and common   component of our diets, it seems strange why we  would need to be warned of its presence. Well,   back to that point zero one percent of folks  we discussed earlier.

Hi, by the way. Certain   individuals simply can’t digest phenylalanine,  or process it into all those helpful substances   we discussed earlier. These people suffer from  a genetic disorder known as phenylketonuria,   or PKU.

There are a few other similar conditions  as well. People with PKU don’t correctly produce   an enzyme called phenylalanine hydroxylase, or  PAH. That enzyme normally converts phenylalanine   to another amino acid, tyrosine, for  further use.

Without functional PAH,   high concentrations of phenylalanine can build up  in the body. And phenylalanine, while necessary,   is actually neurotoxic in high concentrations. Ask  any toxicologist and they’ll tell you: The dose   makes the poison.

It’s the very definition  of too much of a good thing. With too much   phenylalanine swimming around, PKU can result  in numerous negative health effects including   intellectual disability, seizures, tremors, and  ataxia if left untreated. And unfortunately,   treatment isn’t as easy as just passing on the  lentils.

Individuals with PKU normally have to   adhere to a low-phenylalanine diet. This is as  opposite to a high-protein fad diet as you can   possibly get. It means cutting out or reducing  common foods like meat, fish, eggs, cheese,   potatoes, corn, peas, and beans, and diet soda.  Further, because completely eliminating protein   from the diet would cause its own set of problems  for the body, individuals with PKU often have   to take poor-tasting and smelling formulas that  contain other essential nutrients several times   a day.

And if you’ve had this experience,  you may be screaming at the screen, “Yeah,   it’s really hard!” If you are, say hi in the  comments. With so many restrictions, it’s not   uncommon for individuals with PKU to struggle  with maintaining such a rigid diet. Which is   why there’s a lot of motivation to develop other  treatment options.

Over the past few decades,   a breakthrough in PKU treatment has arisen from  a surprising source: plants. In the mid 1950s,   researchers were busy working to discover the  origin of lignin, a chemical that gives plants   rigidity. During their investigations, however,  they found that the plants they were examining   were using an enzyme called PAL, not PAH, to break  down phenylalanine into smaller compounds.

So   throughout the next six decades, a hodgepodge of  international researchers from various entities,   private and public, gradually built upon that  fortuitous finding. They were working to see   whether PAL could do for humans what it does  for plants. And it seems, for the most part,   PAL is really good at breaking down phenylalanine  into harmless byproducts the body can simply flush   out.

In 2018, PAL became available for daily use  by injection to help manage phenylalanine levels.  Plus, it potentially allows people with PKU to  transition to a more typical diet. Which means   finally enjoying a delicious, hot bowl of lentils.  Every kid’s dream. But PAL can have serious side   effects for certain users.

So, researchers have  also been looking into other solutions. By 2019,   multiple teams of scientists had launched various  types of gene-therapy experiments to treat this   disease, using mouse models of PKU. That’s right.  A mouse who also can’t drink diet soda.

In one   experiment, these brave, furry participants  received injections of genetically edited,   PAH-producing viruses into their livers to help  produce the enzyme. Instead of making the mice   sick, these so-called viral vectors would read out  the gene for PAH. And, the results were promising:   the mice were able to sustain suitable  phenylalanine blood levels for a period of   17 weeks.

But, if you’ve ever read Steinbeck,  you’ll know there’s a big difference between   Mice and Men. So, more research is underway  to determine the safety and efficacy of these   kinds of therapies in humans. Lastly, if you’re  wondering if you could have PKU, and need to mind   those soda warnings, you probably already know if  you have it.

PKU tests have been routinely given   to newborns in many countries since around the  mid-1970s. And, for individuals living with PKU,   maintaining vigilance over how much phenylalanine  is ingested is still a daily challenge. Hence,   the explicit advertisement on diet soda  cans.

So, now you know, the next time you   see an unfamiliar warning on a product, even  if it doesn’t affect you, there is a reason,   because it could potentially be life-saving  to someone else. So carry on with your soda.  Disclaimers for things like phenylalanine are the  soda brand’s version of open and honest discourse   with you, the consumer. If you’re looking for a  product that goes beyond disclosure requirements   and offers behind the scenes intel, you’ll  find it in Linode.

Linode is a cloud computing   company from Akamai that powers the internet  worldwide through storage space, databases,   analytics and more. But they don’t keep all  of that power to themselves. Their platform’s   cloud manager source code is available online,  so anyone can access it.

They even take it one   step further by explaining how the code works  and how you can use it in video tutorials,   written guides, and real live customer support  representatives available 365 days of the year.   You can see all of Linode’s tools and services  by clicking the link in the description down   below or heading to linode.com/scishow. That  link gives you a $100 60-day credit on a new   Linode account. Thanks to Linode for supporting  this SciShow video and thank you for watching!  [♪ OUTRO]