Children who suffer from a lack of HGH are often a normal size when born. Some children are unable to produce HGH when they are born and remain deficient throughout their life. In some children, a lack of HGH is part of a genetic condition. In many others, the cause of the deficiency is unknown. The naturally occurring growth hormone of humans or a genetically engineered form that is used in treatment of children with growth hormone deficiencies and has been used especially by athletes to increase muscle mass.