Most healthy children between the ages of four and 10 grow about five centimeters a year. Parents often notice this growth by how quickly their children grow out of their clothes and shoes.

However, when a child does not reach usual growth markers, it could be a sign of a health problem.

One American family knew something might be wrong when their son was able to fit into the same clothes, season after season.

Spencer Baehman is a boy who loves to play baseball. "My goal is to play college baseball."

But at age 11, he was much shorter than everyone on his team. Although his small size did not stop Spencer from playing the sport he loves, it did make him feel different. "I want to be as tall as these kids."

At first, Spencer's parents thought their son was just small. But over time, they began to worry that something was wrong.

When springtime came around and baseball season started, Spencer tried on his old cleats -- a type of sports shoe. They still easily fit on his feet.

That is when his mom called the doctor. "It really set in one year coming out of winter into spring when he got out his cleats for spring baseball and he put them on, and they fit. And they never should have fit. Those were from the spring prior."

Spencer's parents went to see Dr. Bert Bachrach. He is the chief of pediatric endocrinology at University of Missouri Health Care. After much measuring and testing, Dr. Bachrach found the cause of Spencer’s growth failure: a growth hormone deficiency. In other words, Spencer’s body was not making enough growth hormone.

Hormones are chemicals in the body. They send messages from one cell to another. Growth hormones are necessary for physical growth in children. The levels of growth hormone rise throughout childhood. The levels are highest during puberty.

This hormone helps to control many functions in the body. Dr. Bachrach explains.

"Growth hormone just doesn't affect your growth, it affects your muscle mass and fat distribution. So that affects your cholesterol. It also affects your overall sense of well-being."

Growth hormone deficiency is a disorder involving the pituitary gland. The pituitary gland is small -- about the size of a pea. It is located at the base of the brain. This small gland produces many hormones, not just the growth hormone.

Several things can affect the pituitary gland’s ability to produce growth hormones.

Growth hormone deficiency is mainly the result of damage to the pituitary gland, or hypothalamus, while the fetus is growing in the mother’s womb. It can also happen as a result of a genetic mutation.

And in some cases, children who severely lack emotional and social experiences do not produce enough growth hormone and stop growing. These children often start growing again when they begin receiving the care and human interaction they need.

In Spencer’s case, he needed daily hormone injections. His mother has been giving him the injection every day for the past two years. In that time, Spencer has grown about 15 centimeters.

But just in case he does not grow as tall as he would like, he has a reminder to himself written into each of his baseball hats.

"It says HDMH -- which means ‘height doesn't measure heart’." When used this way, “heart” means bravery, determination and emotional strength -- all things that Spencer is not in short supply of.