(NewsNation) — At least four babies have been hospitalized in South Carolina since the nationwide baby formula shortage started. Companies abroad, such as Danone and Nestlé, are helping efforts to send 5 million bottles of formula to the U.S. for babies with allergies.

But parents of 4-year-old Greyson Endrizzi say their son has a metabolic disease and they have run out of his special formula.

Greyson’s parents, Kim Endrizzi and Mark Endrizzi, said their son drinks formula that gives him 80 percent of his nutrition.

“It impacts his brain if he doesn’t have his formula. We do blood tests, and there are neurotoxins building up in his brain,” Kim Endrizzi told NewsNation.

Greyson has a rare disease called phenylketonuria, or for PKU for short. PKU affects his metabolism and makes it so he cannot metabolize amino acids. He’s been forced to drink formula since he was 6 days old.

Kim Endrizzi explained that if their son doesn’t have formula long-term, PKU could become a permanent disability for him.

The Department of Health and Human Services recommends parents reach out to health care providers in the meantime for ways to find formula. The Endrizzis said they’ve called their pediatrician to see where they can scrounge for formula, but there is nothing available.

“You can’t buy it off the internet. You can’t get it at the stores. The stores themselves are bare shelves,” Mark Endrizzi told NewsNation.

And they’ve even rationed formula doses for weeks now, but there have been side effects: “It’s been obvious in observing him, we’ve noticed the differences physically and emotionally,” Mark Endrizzi continued.

Greyson’s parents said he’s been sad, angry and confused. His teachers have even commented on his changes.

“He’s only 4 and a half; he doesn’t understand that he’s been in a fight for the past few months. He doesn’t understand why he’s feeling the way he’s feeling. He’s just acting out because he doesn’t know what else to do,” Mark Endrizzi said.

It’s not clear when more formula will be available. Mark Endrizzi believes the dates aren’t accurate when it comes to expected shipments.

The FDA announced it is working to increase the supply of prescription formula and Americans should begin seeing adequate supplies in coming weeks.

“Actually three more weeks from now. We planned for two weeks with formula, now what are we going to do?” Mark Endrizzi questioned.

The only other option is pills.

“He would need hundreds of these pills that would be equivalent to his formula and a 4-year-old can’t swallow pills,” Kim Endrizzi said.

Greyson’s parents explained that PKU is a lifelong illness, and that adults need this formula, too.

Mark Endrizzi said, “This is a dire situation for more people than you would imagine, and it’s not an allergy. This, we are talking life or death.”

The Endrizzis said some parents are asking doctors if they can use expired formula. Kim mentioned if he gets bad enough, they may consider hospitalizing their son, and putting him on a feeding tube.

This is part of “Morning in America’s” Economic Brain Room.