Turner syndrome, or congenital ovarian hypoplasia syndrome. Humans have 23 pairs of 46 chromosomes, one of which is the sex chromosome. Boys have one X chromosome and one Y chromosome each, and girls have both sex chromosomes as X chromosomes. If a girl has only one X chromosome, or if part of the X chromosome is missing, Turner syndrome can occur. Because the X chromosome contains many genes (1000), the loss can cause many problems or even serious problems, with gonadal insufficiency being one of the main problems. In fact, a Turner syndrome fetus can have millions of germ cells in the middle of the mother’s gestation, but then they are rapidly reduced, leaving only a few follicles in the fibrous cords at birth, resulting in gonadal insufficiency. As a result of hypogonadism, the ovaries produce low levels of estrogen, and about one-third of girls with Turner syndrome have spontaneous puberty, but only half of them have their first menstrual period. The effects of hypogonadism are not limited to the reproductive system, but can also affect many systems, organs or tissues such as the cardiovascular system, lipid metabolism, glucose metabolism, liver function and the nervous system due to low estrogen levels. Hypogonadism leads to overproduction of gonadotropins by the pituitary gland and can have two periods of peak production during childhood. The first peak occurs in infancy, then gradually declines, dropping to a minimum at 7-8 years of age, followed by an upward trend and a second peak at 9-11 years of age, and reaching menopausal levels. Therefore, gonadotropin levels can be monitored to predict future gonadal function as well as to determine the appropriate timing and dosage of estrogen replacement therapy. The goal of estrogen replacement therapy in girls with Turner syndrome is to normalize the development of secondary sexual characteristics, which include breast size and shape, size and shape of the potentially reproductive uterus, bone growth and mineral gains, cardiovascular function, brain development, liver function, and other estrogen-dependent developmental processes. If growth hormone therapy is initiated early and the type of estrogen, dose and mode of administration of estrogen therapy is carefully selected so that normal secondary sexual characteristics appear at the age of normal childhood puberty, it is possible to achieve normal adult height. Hormone replacement therapy is generally available by oral and transdermal routes of administration. In general, transdermal administration in the form of estrogen patches or gels is the only form of treatment to bring estrogen to natural levels in the blood. If oral estrogens, such as ethinyl estradiol, are administered orally, most of them undergo first-pass metabolism in the liver, where most of them are in turn converted to estrone sulfate. Mixed estrogens of equine origin are mixtures of hormones containing estrogen, progestin and androgens, some of which have not been identified in humans, and there is no evidence-based basis for the use of such drugs in children. Although both oral therapy and transdermal routes of estrogen administration may prevent atherosclerosis, oral estrogen therapy increases resistance to activated protein C and decreases antithrombin III activity, thereby increasing the risk of thrombosis. A case-control study of 155 consecutive hospitalized women showed that oral administration of estradiol increased the risk of pulmonary vein thrombosis fourfold compared with transdermal administration in women with a first episode of idiopathic venous embolism. Oral estradiol also increases C-reactive protein; causes growth hormone resistance; decreases insulin-like growth factor 1 and insulin-like growth factor binding protein 3 levels; increases sex hormone-binding globulin, leading to decreased testosterone utilization; and increases triglycerides in LDL and HDL particles, making them more likely to cause atherosclerosis. Transdermal estradiol administration barely affects these parameters. These studies have not been confirmed by large randomized trials with mostly postmenopausal women; therefore, the utility in young and adolescent patients with Turner syndrome remains to be confirmed. If transdermal estradiol is not available, oral estradiol or ethinyl estradiol should be considered. The following various doses are considered equivalent (although equivalence is based on which assay is used and clinical assessment endpoints): 100ug transdermal estradiol = 2mg oral estradiol = 20ug ethinyl estradiol = 1.25mg equine urinary mixed estrogen. Because of the high estrogen/progestin ratio of oral contraceptives, avoid oral contraceptives whenever possible. Androgen replacement therapy is not a standard treatment option. However, a recent randomized, double-blind, placebo-controlled, cross-matched preliminary study showed significant benefits of androgen replacement therapy (1.5 mg methyltestosterone) for Turner syndrome on bone health, lipid metabolism, body composition and quality of life, while cognitive function was affected to varying degrees.