研究：个子矮小皆因基因数量不足

　　A shortage of genes could be to blame for the lack of height in short people, researchers have found.

　　Two studies involving 12,000 people has been carried out in America and found a link between the amount of missing genetic material and a decrease in height.

　　Height is mostly passed down through families but scientists say this does not explain everything when comparing the variations between people.

　　Dr Joel Hirschhorn, who led a study published in the American Journal of Human Genetics, said: "Despite tremendous recent progress in finding common genetic variants associated with height, thus far these variants only explain about 10 percent of the variation in adult height."

　　Researchers now believe that missing copies of genes or other sections of DNA could be the reason behind up to half of the genetic impact on people's height.

　　Known as copy number variants (CNV)， the genetic abnormalities are alterations within the chromosome which means a cell has an excess or an absence of a slice of DNA.

　　Some CNVs are common, but others are rare or occur with low frequency among humans.

　　And the researchers found an excess of low frequency CNV deletions - where part of the genome is missing - in shorter people.

　　There is a wide variation in the amount of these CNV deletions which people have in their genome, with some people having several million.

　　The researchers from the Children's Hospital Boston found that for every million individual deletions, one eighth of an inch in height was lost in people.