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。
據英國《每日郵報》11月24日報道，研究人員發現，基因數量不足可能是人身高較低的原因。
在美國進行的兩項涉及1.2萬人的調查研究發現了缺失基因的數量與身高降低之間的關系。
身高主要通過家族遺傳，但是科學家說，在比較人與人之間的不同之處時，這個原因并不能解釋所有問題。
喬爾·何塞豪恩主持了這項研究，研究成果發表在美國的《人類遺傳學》雜志上，他說：“盡管一般的遺傳變異與身高方面關聯的研究近期取得了重大的進展，但迄今為止，這種遺傳變異僅僅能解釋10%的成年人身高變化的原因。”
研究人員現在認為，成人在身高方面受基因影響的背后原因，有一半可能是因為缺失基因副本或是DNA組成部分。
被稱為拷貝數變異(CNV)的基因異常是染色體內部的改變。這意味著，一個細胞可能會多出或缺少一片DNA。
有些拷貝數變異是很常見的，但還有一些則在人類中極少發生或是發生的頻率較低。
研究人員發現，在個子比較矮的人身上，會出現低發生率拷貝數變異過剩——部分基因組缺失。
人類基因組拷貝數變異缺失在數量上也有很大的不同，有些人的缺失數甚至能達到幾百萬。
波士頓兒童醫院的研究人員發現，每一百萬個基因缺失就會使身高下降八分之一英寸。
