Dec. 28, 2010 -- Friendly and playful, Carter Hearn from Lufkin, Texas, may act like a regular, happy-go-lucky little boy, but he suffers from a rare condition that sets him apart from other children. At just four years old, Carter stands at nearly four feet tall and weighs 90 pounds, just a couple inches shorter, but nearly twice as heavy, as his six-year-old sister, Kaylie.
His mother, Deena Hearn, said she first noticed her son's abnormal growth when he weighed almost 30 pounds as an infant.
"I had Kaylie's [baby] book to compare by, and I was like, I just know something is not right. He is not eating that much to be gaining that much weight," Hearn said.
Concerned about their son's health, Hearn took Carter to doctor after doctor, but she said physicians often accused her of simply over-feeding the boy and told her to "get him on a diet."
"They would just look at me, you know, asking me questions about what he ate and what he did," she said. "I actually had one endocrinologist in Houston ask me if I was sleep-walking [and] feeding him."
Hearn added that not just doctors, but other parents and even strangers remarked on Carter's large size.
"When he was in daycare, parents would comment to the workers that they needed to call the child protection services on us for what we were doing to our child, because they assumed we were over-feeding him because he was so big," Hearn said, explaining that her daughter, Kaylie, had the complete opposite body type to Carter's.
"She can eat 24/7 and not gain anything," Hearn said. "That's what I told them...if I was feeding one this way, you think the other would be this way also."
Aside from his unusual girth, Carter suffered from other health problems, including a heart murmur, difficulty breathing and bone deposits under his skin that his mother said felt like pebbles. Hearn became frustrated when none of the doctors in their hometown could figure out what was wrong with her son.
"I felt like they thought I was crazy. I felt like they were the ones supposed to be helping me and they [were] not listening. They [were] blaming me -- it was horrible," she said. "Doctors would sit there and tell me something's wrong with him but, you know, we might not ever find out what it is. I'm like, no that's not a good enough answer."
Carter Finally Gets a Diagnosis
It wasn't until Hearn said she watched a Discovery Health special three years ago on an Australian child, who had a chubby round face and looked just like Carter, that the concerned mother thought they might have solved the mystery of Carter's strange condition. A visit to a physician in Dallas confirmed her suspicions.
"Carter has a syndrome called Albright's Hereditary Osteodystrophy," Hearn explained. "There are two types of it or two subtypes as they call it. He has what's called pseudohypoparathyroidism, Type Ia."
According to the National Institute of Health, pseudohypoparathyroidism, or Albright's for short, is a very rare genetic disorder -- affecting only one in 20,000 people -- in which the body has trouble responding to the parathyroid hormone. People with this disorder produce the right amount of the hormone, but the body is "resistant" to its effect. The mutated genes are passed down through one parent, or occur through a spontaneous mutation of the egg or sperm.
In Carter's case, a Type Ia condition causes short stature, round face and short hand bones. Those common traits are often why many Albright's children can look uncannily similar.
After receiving the diagnosis, Hearn was referred to the Kennedy Krieger Children's Institute in Baltimore to be evaluated by Dr. Emily Germain-Lee, the leading authority on Albright's.
"Parathyroid hormone is important to maintain normal calcium and phosphorus balance in the blood," Germain-Lee said. "If it's not working appropriately, the calcium falls, the phosphorus rises, and eventually the calcium levels get so low the patient can have a seizure."
According to Dr. Germain-Lee, one of the most promising treatments for Albright's currently is growth hormone therapy, which another of her patients, 16-year-old Steven Fraguglia, has been undergoing for the past seven years. The doctor was overjoyed when she saw the progress her patient was making.
"When I see you, I'm just blown away," she said to Fraguglia during an appointment. "Ten years ago when I started this, you are what my hope was. You are the dream of what I wanted to see happen and it happened."
A Possible Treatment for Carter's Condition?
Under the growth hormone treatment, Fraguglia said he grew about 7 inches and now stands about 5 feet, 7 inches tall. Without it, his mother, Linda Fraguglia, said he probably would have been only 5 feet, 1 inch tall.
"I just feel like a normal person now, a normal kid in high school. No one would even realize I have anything different or be any different," Fraguglia said.
Germain-Lee cautioned that the growth hormone therapy isn't a cure-all for this condition.
"Right now, I am looking at methods that I can use at the present in order to improve their quality of life, so not so much a cure, as a taking each problem step by step and improving what's known," she explained. "There is so much to be done in this condition and so little is known."
As for Carter and his family, Hearn said she is hoping to get her son started on growth hormone treatments in the next couple of years, but in the meantime, she also hoped doctors will become more aware of Carter's condition and properly diagnosis other kids dealing with the same thing.
"A lot more kids are being diagnosed and parents have the same story: we were ignored, we were told we were crazy, we were blamed for it," she said. "I'm hoping the word's getting out more."
ABC News' Lauren Effron contributed to this report.