These brothers from Georgia have seen a lot of highs and lows together.

Nick and Levi Smith, from Commerce, Georgia, may only be three years apart in age, but younger brother Levi, 25, towers 4 feet over Nick, 28.

That’s because Nick, at just 2-foot-6, has microcephalic osteodysplastic primordial dwarfism (MOPD) type 2, a rare genetic disorder that also makes him susceptible to illnesses usually associated with old age.

Meanwhile, Levi, along with other brother Travis, clock in at 6-foot-5.

When the family, including mom, Shelly, who is 5-foot-8 got together to celebrate Nick’s recent birthday, it was no small occasion.

“We didn’t even know that we would have him for 28 years and we don’t know if we’ll have him for 29,” Shelly tells Born Different.

“I worry about Nick’s future every day,” she continues. “I worry about a small cold that might end up with something worse.”

MOPD is a severe form of dwarfism which becomes evident even before birth, and is associated with premature death, often before age 30. According to the National Institutes of Health, the disorder affects fewer than 200,000 people in the US.

Aside from a truncated stature, the condition is also characterized by an unusually small head size (microcephaly), hip dysplasia, scoliosis and distinctive facial features, including a prominent nose, high cheekbones and small jaw.

“Nick has done everything more than the doctors imagined,” says Shelly, who reports on Nick’s life for their nearly 17,000 subscribers on YouTube. A video produced by Born Different and posted to Nick’s Facebook fan page has garnered nearly 920,000 views.

She jokes, “To be born into my family where my ex-husband is 6’8″ and my boys are 6’5″ and I’m 5’8″, and then you got Nick — I said, ‘God had a sense of humor when he made my family.’ ”

Adds brother Travis, “Celebrating Nick’s birthday is always a great thing, celebrating his life and being here with us.”

“Nick will always be in my nest . . . I will always have that mama role,” says Shelly. “It’s like having that boy that never grew up. It’s a beautiful child to have.”

One famous example of an individual with MOPD was 19th-century Mexican sideshow performer Lucía Zárate, who lived from 1864 to 1890. Zárate was immortalized by Guinness World Records for “lightest recorded adult,” weighing a mere 4.7 pounds at 17 years old. She died of hypothermia at age 26 when her circus train was stranded in California’s snowy Sierra Nevada.