Patients with GHD should be diagnosed and treated early in order to achieve maximum height gain in prepubertal period. For the initiation of treatment in Turner syndrome, GH therapy should be started when height is below the 5th percentile of the normal female growth curve, which can be as early as 2 years of age [9]. However, there is a lack of sufficient evidence-based medical evidence regarding the long-term efficacy and safety of growth hormone therapy for children who start growth hormone therapy at a younger age.The height index for ISS therapy is 2-3 standard deviations below the mean height, and the recommended age for starting therapy is 5 years to early adolescence [6]. The majority of children with SGA are born with catch-up growth and reach the normal range, but 10%-15% still fail to catch up, and about half of them will be 2 standard deviations below the normal mean height by the time they reach adulthood, and growth hormone can be applied to these children to improve their final height. Domestic and international opinions are not unanimous regarding the age of initiation of treatment for children younger than fetal age. The US FDA recommends starting growth hormone therapy for children younger than 2 years of age who have not achieved catch-up growth. The European EMEA recommends growth hormone therapy for children over 4 years of age who are 2.5 standard deviations below the mean height; whose growth rate is lower than the mean for the same age; and whose height is 1 standard deviation below the genetic target height. The International Society for Pediatric Endocrinology and the GH Research Society recommend starting rhGH therapy for younger children aged 2-4 years without catch-up growth and with a height below 2.5 standard deviations from the mean height; for younger children aged 4 years or older without catch-up growth and with a height below 2-2.5 standard deviations, there is no consensus on whether to apply growth hormone therapy, but most experts believe that a height below 2 standard deviations can be considered for growth hormone therapy. However, most experts believe that growth hormone therapy can be considered for children with a height below 2 standard deviations. There is no consensus on the age of onset of treatment for Prader-Willi syndrome, but it is generally accepted that it is beneficial to start growth hormone therapy before the onset of obesity, i.e., around 2 years of age.