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Scientists find gene that may cause shortness

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Why are really short people so short? It's largely a mystery. But now scientists have discovered a gene that might cause some cases.

Follow-up work might help scientists understand the biology of what determines a person's height and lead to new drugs that could make short children taller.The recent study defined "short" as belonging to the shortest 2.5 percent of the population. That's a standard cutoff. For American men, that translates to about 5-foot-4 and under; for American women it's just under 5 feet.

Nobody knows exactly why most people in this group are so short. Genes clearly play a role, but few genes that stunt growth have been identified. Other factors like nutrition and environment also clearly enter in.

Most of these people are healthy, so medical conditions can explain only a small percentage.

The newly found gene is called SHOX. Researchers found it was damaged in one person out of a group of 91 healthy short people, or about 1 percent.

The mutation didn't show up in 300 DNA samples from people of normal height.

The short person who showed the mutation was a girl who stood 35 inches tall at age 4. On average, girls in the United States are about 40 inches tall on their fourth birthdays.

The researchers looked at DNA from several generations of the girl's family, which lived in Germany. They found the SHOX gene flaw in all five family members who met the criteria for shortness but not in three family members who didn't.

The SHOX gene is a "strong candidate" for causing some cases of shortness, researchers from Germany, the Netherlands and Japan wrote in the journal Nature Genetics.

Dr. Judith Ross, a pediatric endocrinologist at Thomas Jefferson University in Philadelphia, called the results provocative. But it would take more work to prove that a mutated SHOX gene really makes people short, she said.

In the analysis of the German girl's family, the result depended heavily on the definition of "short," she said. Two family members who were classified as normal height would have been called short if they were less than an inch shorter, she said.