Isolated hypogonadotropic hypogonadism (IHH), also called idiopathic or congenital hypogonadotropic hypogonadism (CHH) as well as isolated or congenital gonadotropin-releasing hormone deficiency (IGD) accounts for a small subset of cases of hypogonadotropic hypogonadism (HH) due to deficiency in or insensitivity to gonadotropin-releasing hormone (GnRH) where the function and anatomy of the anterior pituitary are otherwise normal and secondary causes of HH are not present. Primary or secondary
Primary - defect is inherent within the gonad: e.g. Noonan syndrome, Turner syndrome (45X,0), Klinefelter syndrome (47XXY), XY with SRY gene-immunity
Secondary - defect lies outside of the gonad: e.g. Polycystic ovary syndrome, and Kallmann syndrome, also called hypogonadotropic hypogonadism. Hemochromatosis and diabetes mellitus can be causes of this as well. Congenital vs. acquired
Examples of congenital causes of hypogonadism, that is, causes that are present at birth:Turner syndrome and Klinefelter syndrome. It is also one of the signs of CHARGE syndrome. Examples of acquired causes of hypogonadism:Opioid Induced Androgen Deficiency (resulting from the prolonged use of opioid class drugs, e.g. codeine, Dihydrocodeine, morphine, oxycodone, methadone, fentanyl, hydromorphone, etc.) Anabolic steroid-induced hypogonadism (ASIH)
Childhood mumps
Children born to mothers who had ingested the endocrine disruptor diethylstilbestrol for potential miscarriage
Traumatic brain injury, even in childhood
In males, normal aging causes a decrease in androgens, which is sometimes called "male menopause" (also known by the coinage "manopause"), late-onset hypogonadism (LOH), and "andropause" or androgen decline in the aging male (ADAM), among other names. It is a symptom of  hereditary hemochromatosis

Hormones vs. fertility
Hypogonadism can involve just hormone production or just fertility, but most commonly involves both.
It is particularly indicated in men with hypogonadism who wish to retain their fertility, as it does not suppress spermatogenesis (sperm production) as testosterone replacement therapy does.For both men and women, an alternative to testosterone replacement is low-dose clomifene treatment, which can stimulate the body to naturally increase hormone levels while avoiding infertility and other side effects that can result from direct hormone replacement therapy. Clomifene blocks estrogen from binding to some estrogen receptors in the hypothalamus, thereby causing an increased release of gonadotropin-releasing hormone and subsequently LH from the pituitary. Clomifene is a selective estrogen receptor modulator (SERM). Generally, clomifene does not have adverse effects at the doses used for this purpose. Clomifene at much higher doses is used to induce ovulation and has significant adverse effects in such a setting. See also
References
External links
Isolated Gonadotropin-Releasing Hormone (GnRH) Deficiency Overview at National Center for Biotechnology Information. MedlinePlus Encyclopedia: Hypogonadism
Hypogonadism at eMedicine