HACKENSACK, N.J. — Imagine tucking your two boys in bed every night knowing that neither of them is likely to live long enough to graduate from high school. It’s a daily reality for Jeff and Deena Leider of Garfield, N.J.

Their sons, Jason, 6, and Justin, 3, were born with a rare genetic disease, Hunter syndrome, in which their bodies fail to produce a key enzyme needed to maintain healthy cells. Despite costly enzyme replacement therapy, their cells don’t dispose of toxins, and as they grow, their organs swell and their bodies steadily shut down. Most kids with Hunter syndrome don’t make it past 15.

The boys were busy coloring with crayons while their father explained their disease to students at the Fortis Institute in Wayne, N.J., last week.

“Every day, when I kiss them goodnight, I leave their room and get choked up knowing that we’re one day closer to the final chapter,” Leider told the students. “But I don’t have time to cry right now. As their daddy and their provider, I can only fight for them.”

Leider, a landscaper by trade, spends as much time as he can spreading the word about Hunter syndrome, which was first diagnosed in 1906 but is exceedingly rare. There are only about 300 cases nationwide, and his two boys are among four cases reported in New Jersey, he said.

He’s working with state Sen. Nellie Pou, D-Hawthorne, on a bill that would require that all newborns be tested for Hunter syndrome. Only one state — Texas — requires testing, he said.

Leider, with his wife, has created a foundation — Let Them Be Little X2 — with its own website to raise money and awareness. Two years ago he testified before Congress and helped persuade the Obama administration to cut red tape involving clinical trials so that experimental drugs to combat genetic illnesses could be put on the market more quickly. He’s written a soon-to-be-published book, “Our Journey Home,” which he hopes will raise money.

The students at Fortis donated $500 to Leider’s foundation, the proceeds from a recent fundraiser.

Leider said his first-born son, Jason, seemed like a healthy kid at first — except that he had chronic ear infections and his nose kept running. At age 3, Jason’s preschool teacher noticed that the boy kept rolling his tongue.

A blood test revealed Hunter syndrome; the Leiders then had Justin tested, and he proved to have the disease, too.

Hunter syndrome strikes only boys, and Jason and Justin have all the telltale signs of the disease: their hair is coarse and their noses are flat.

The boys look like twins — all Hunter syndrome children look alike — and Jason is already developing a paunch due to swelling of the abdomen.