A genetic cause of gigantism, a rare condition that leads to excessive growth in children, may have been identified, researchers say.

Children with gigantism grow rapidly, become abnormally tall, have large hands and feet, and sometimes experience a delay in puberty.

The condition results from an excess of growth hormone produced by the pituitary gland.

Gigantism is sometimes treated by removing part or all of the pituitary, but it can in some cases be treated using medication alone.

Now, researchers with the National Institutes of Health say they've observed a duplication of a small stretch of the X chromosome in a number of people with the disorder, which is also sometimes seen in adults, where it is known as acromegaly.

One single gene within the identified region of the chromosome has a major effect on how much children will grow and the rate at which they do so, the researchers report in the New England Journal of Medicine.

A study headed by Dr. Constantine Stratakis at the U.S. National Institute of Child Health and Human Development began with a family that came to the NIH for treatment of gigantism in the mid-1990s, with the mother was well as two of her sons displaying the condition.

"Giants are very rare," Stratakis says. "If you have three cases in the same family, that is very rare."

The researchers turned to whole-genome studies to look for significant changes in DNA that might be linked to the condition.

Subsequent studies of 43 people with gigantism in their childhood found they all possessed a duplication of the same region of their X chromosome.

The researchers focused on a gene known as GPR101, found to a thousand times more active in the pituitary glands of children with gigantism than in normal children, even within the same family.

"We believe GPR101 is a major regulator of growth," Stratakis says. "Understanding how children grow is extraordinarily important, as an indicator of their general health and their future well-being."

The findings could yield effective treatments for gigantism, the researchers say, and might even lead to better understanding of the opposite condition in children -- undergrowth -- which is normally treated by giving them additional growth hormone.

"Finding the gene responsible for childhood overgrowth would be very helpful, but the much wider question is what regulates growth," Stratakis said.

Both excessive and inadequate growth as seen in children are likely controlled by the identical physiological mechanisms, he says.