It is also known that disruption of the endocrine system by certain chemicals adversely affects the development of the reproductive system and can cause vaginal cancer. Many other reproductive diseases have also been link to exposure to synthetic and environmental chemicals. Common chemicals with known links to reproductive disorders include: lead, dioxins and dioxin-like compounds, styrene, toluene, BPA (Bisphenol A) and pesticides.

Examples of congenital abnormalities of the reproductive system include:

- Kallmann syndrome - Genetic disorder causing decreased functioning of the sex hormone-producing glands caused by a deficiency or both testes from the scrotum.

- Androgen insensitivity syndrome - A genetic disorder causing people who are genetically male (i.e. XY chromosome pair) to develop sexually as a female due to an inability to utilize androgen.

- Intersexuality - A person who has genitalia and/or other sexual traits which are not clearly male or female.

The following are some of the possible medical causes of galactorrhea hyperprolactinemia that are listed by the Diseases Database: pregnancy, breastfeeding, sexual intercourse, shingles, prolactin secreting pituitary tumor, along with many others.

Hyperplasia may be due to any number of causes, including increased demand (for example, proliferation of basal layer of epidermis to compensate skin loss), chronic inflammatory response, hormonal dysfunctions, or compensation for damage or disease elsewhere. Hyperplasia may be harmless and occur on a particular tissue. An example of a normal hyperplastic response would be the growth and multiplication of milk-secreting glandular cells in the breast as a response to pregnancy, thus preparing for future breast feeding.

Perhaps the most interesting and potent effect IGF has on the human body is its ability to cause hyperplasia, which is an actual splitting of cells. By contrast, hypertrophy is what occurs, for example, to skeletal muscle cells during weight training and steroid use and is simply an increase in the size of the cells. With IGF use, one is able to cause hyperplasia which actually increases the number of muscle cells present in the tissue. Weight training with or without anabolic steroid use enables these new cells to mature in size and strength. It is theorized that hyperplasia may also be induced through specific power output training for athletic performance, thus increasing the number of muscle fibers instead of increasing the size of a single fiber.

Symptoms of galactorrhea hyperprolactinemia include a high blood prolactin level, abnormal milk production in the breast, galactorrhea, menstrual abnormalities, reduced libido, reduced fertility, puberty problems, and headaches.

Approximately 10–25 percent of cases are estimated to result from the use of medications. This is known as non-physiologic gynecomastia. Medications known to cause gynecomastia include ketoconazole, cimetidine, gonadotropin-releasing hormone analogues, human growth hormone, human chorionic gonadotropin, 5α-Reductase inhibitors such as finasteride and dutasteride, estrogens such as those used in transgender women and men with prostate cancer, and antiandrogens such as bicalutamide, flutamide, and spironolactone. Medications that are probably associated with gynecomastia include calcium channel blockers such as verapamil, amlodipine, and nifedipine; risperidone, olanzapine, anabolic steroids, alcohol, opioids, efavirenz, alkylating agents, and omeprazole. Certain components of personal care products such as lavender or tea tree oil and certain supplements such as dong quai and "Tribulus terrestris" have been associated with gynecomastia.

Gynecomastia is thought to be caused by an altered ratio of estrogens to androgens mediated by an increase in estrogen production, a decrease in androgen production, or a combination of these two factors. Estrogen acts as a growth hormone to increase the size of male breast tissue. The cause of gynecomastia is unknown in around 25% of cases. Drugs are estimated to cause 10–25% of cases of gynecomastia.

Certain health problems in men such as liver disease, kidney failure or low testosterone can cause breast growth in men. Drugs and liver disease are the most common cause in adults. Other medications such as methadone, aldosterone antagonists (spironolactone and epelerenone), HIV medication, cancer chemotherapy, hormone treatment for prostate cancer, heartburn and ulcer medications, calcium channel blockers, antifungal medications such as ketoconazole, antibiotics such as metronidazole, tricyclic antidepressants such as amitriptyline, herbals such as lavender, tea tree oil, and dong quai are also known to cause gynecomastia. Phenothrin, an insecticide, possesses antiandrogen activity, and has been associated with gynecomastia.

Secondary sexual development induced by sex steroids from other abnormal sources is referred to as "peripheral precocious puberty" or "precocious pseudopuberty." It typically presents as a severe form of disease with children. Symptoms are usually as a sequelae from adrenal insufficiency (because of 21-hydroxylase deficiency or 11-beta hydroxylase deficiency, the former being more common), which includes but is not limited to hypertension, hypotension, electrolyte abnormalities, ambiguous genitalia in females, signs of virilization in females. Blood tests will typically reveal high level of androgens with low levels of cortisol.

Causes can include:

- Endogenous sources

- gonadal tumors (such as arrhenoblastoma),

- adrenal tumors,

- germ cell tumor,

- congenital adrenal hyperplasia,

- McCune–Albright syndrome,

- Exogenous hormones

- Environmental exogenous hormones,

- As treatment for another condition.

Hyperplasia is considered to be a physiological (normal) response to a specific stimulus, and the cells of a hyperplastic growth remain subject to normal regulatory control mechanisms. However, hyperplasia can also occur as a pathological response, if an excess of hormone or growth factor is responsible for the stimuli. Similarly to physiological hyperplasia, cells that undergo pathologic hyperplasia are controlled by growth hormones, and cease to proliferate if such stimuli are removed. This differs from neoplasia (the process underlying cancer and benign tumors), in which genetically abnormal cells manage to proliferate in a non-physiological manner which is unresponsive to normal stimuli. That being said, the effects caused by pathologic hyperplasia can provide a suitable foundation from which neoplastic cells may develop.

Several studies have shown that hypopituitarism is associated with an increased risk of cardiovascular disease and some also an increased risk of death of about 50% to 150% the normal population. It has been difficult to establish which hormone deficiency is responsible for this risk, as almost all patients studied had growth hormone deficiency. The studies also do not answer the question as to whether the hypopituitarism itself causes the increased mortality, or whether some of the risk is to be attributed to the treatments, some of which (such as sex hormone supplementation) have a recognized adverse effect on cardiovascular risk.

The largest study to date followed over a thousand people for eight years; it showed an 87% increased risk of death compared to the normal population. Predictors of higher risk were: female sex, absence of treatment for sex hormone deficiency, younger age at the time of diagnosis, and a diagnosis of craniopharyngioma. Apart from cardiovascular disease, this study also showed an increased risk of death from lung disease.

Quality of life may be significantly reduced, even in those people on optimum medical therapy. Many report both physical and psychological problems. It is likely that the commonly used replacement therapies do not completely mimic the natural hormone levels in the body. Health costs remain about double those of the normal population.

Hypopituitarism is usually permanent. It requires lifelong treatment with one or more medicines.

Multiple Endocrine Neoplasia type 1 (MEN1) is a rare hereditary endocrine cancer syndrome characterized primarily by tumors of the parathyroid glands (95% of cases), endocrine gastroenteropancreatic (GEP) tract (30-80% of cases), and anterior pituitary (15-90% of cases). Other endocrine and non-endocrine neoplasms including adrenocortical and thyroid tumors, visceral and cutaneous lipomas, meningiomas, facial angiofibromas and collagenomas, and thymic, gastric, and bronchial carcinoids also occur. The phenotype of MEN1 is broad, and over 20 different combinations of endocrine and non-endocrine manifestations have been described. MEN1 should be suspected in patients with an endocrinopathy of two of the three characteristic affected organs, or with an endocrinopathy of one of these organs plus a first-degree relative affected by MEN1 syndrome.

MEN1 patients usually have a family history of MEN1. Inheritance is autosomal dominant; any affected parent has a 50% chance to transmit the disease to his or her progeny. MEN1 gene mutations can be identified in 70-95% of MEN1 patients.

Many endocrine tumors in MEN1 are benign and cause symptoms by overproduction of hormones or local mass effects, while other MEN1 tumors are associated with an elevated risk for malignancy. About one third of patients affected with MEN1 will die early from an MEN1-related cancer or associated malignancy. Entero-pancreatic gastrinomas and thymic and bronchial carcinoids are the leading cause of morbidity and mortality. Consequently, the average age of death in untreated individuals with MEN1 is significantly lower (55.4 years for men and 46.8 years for women) than that of the general population.

Many causes of early puberty are somewhat unclear, though girls who have a high-fat diet and are not physically active or are obese are more likely to physically mature earlier. "Obese girls, defined as at least 10 kilograms (22 pounds) overweight, had an 80 percent chance of developing breasts before their ninth birthday and starting menstruation before age 12 – the western average for menstruation is about 12.7 years." Exposure to chemicals that mimic estrogen (known as xenoestrogens) is a possible cause of early puberty in girls. Bisphenol A, a xenoestrogen found in hard plastics, has been shown to affect sexual development. "Factors other than obesity, however, perhaps genetic and/or environmental ones, are needed to explain the higher prevalence of early puberty in black versus white girls." While more girls are increasingly entering puberty at younger ages, new research indicates that some boys are actually starting later (delayed puberty). "Increasing rates of obese and overweight children in the United States may be contributing to a later onset of puberty in boys, say researchers at the University of Michigan Health System."

High levels of beta-hCG in serum and cerebrospinal fluid observed in a 9-year-old boy suggest a pineal gland tumor. The tumor is called a "chorionic gonadotropin secreting pineal tumor". Radiotherapy and chemotherapy reduced tumor and beta-hCG levels normalized.

In a study using neonatal melatonin on rats, results suggest that elevated melatonin could be responsible for some cases of early puberty.

Familial cases of idiopathic central precocious puberty (ICPP) have been reported, leading researchers to believe there are specific genetic modulators of ICPP. Mutations in genes such as LIN28, and LEP and LEPR, which encode leptin and the leptin receptor, have been associated with precocious puberty. The association between LIN28 and puberty timing was validated experimentally in vivo, when it was found that mice with ectopic overexpression of LIN28 show an extended period of pre-pubertal growth and a significant delay in puberty onset.

Mutations in the kisspeptin (KISS1) and its receptor, KISS1R (also known as GPR54), involved in GnRH secretion and puberty onset, are also thought to be the cause for ICPP However, this is still a controversial area of research, and some investigators found no association of mutations in the LIN28 and KISS1/KISS1R genes to be the common cause underlying ICPP.

The gene MKRN3, which is a maternally imprinted gene, was first cloned by Jong et al in 1999. MKRN3 was originally named Zinc finger protein 127. It is located on human chromosome 15 on the long arm in the Prader-Willi syndrome critical region2, and has since been identified as a cause of premature sexual development or CPP. The identification of mutations in MKRN3 leading to sporadic cases of CPP has been a significant contribution to better understanding the mechanism of puberty. MKRN3 appears to act as a "brake" on the central hypothalamic-pituitary access. Thus, loss of function mutations of the protein allow early activation of the GnRH pathway and cause phenotypic CPP. Patients with a MKRN3 mutation all display the classic signs of CCP including early breast and testes development, increased bone aging and elevated hormone levels of GnRH and LH.

When inherited, multiple endocrine neoplasia type 2 is transmitted in an autosomal dominant pattern, which means affected people have one affected parent, and possibly affected siblings and children. Some cases, however, result from spontaneous new mutations in the "RET gene". These cases occur in people with no family history of the disorder. In MEN2B, for example, about half of all cases arise as spontaneous new mutations.

A recommend surveillance program for Multiple Endocrine Neoplasia Type 1 has been suggested by the International Guidelines for Diagnosis and Therapy of MEN syndromes group.

IHH is divided into two syndromes: IHH with olfactory alterations or anosmia, Kallmann syndrome and IHH with normal smell (normosmic IHH).

Kallmann syndrome is responsible for approximately 50% of all cases of the condition. It is associated with mutations in "KAL1", "FGFR1/FGF8", "FGF17", "IL17RD", "PROKR2", "NELF", "CHD7"(which positively regulates GnRH secretion), HS6ST1, "FLRT3", "SPRY4", DUSP6, "SEMA3A", and "WDR11 (gene)", genes which are related to defects in neuronal migration.

Gene defects associated with IHH and normal smell include "PROKR2, FGFR1, FGF8, CHD7, DUSP6," and "WDR11", as in KS, but in addition

also mutations in "KISS1R", "TACR3", GNRH1/GNRHR, LEP/LEPR, HESX1, FSHB, and LHB.

GnRH insensitivity is the second most common cause of IHH, responsible for up to 20% of cases.

A minority of less than 5-10% is due to inactivating mutations in genes which positively regulate GnRH secretion such as ,"CHD7", "KISS1R", and "TACR3".

The causes of about 25% of all IHH cases are still unknown.

Isolated hypogonadotropic hypogonadism (IHH), also called idiopathic or congenital hypogonadotropic hypogonadism (CHH), as well as isolated or congenital gonadotropin-releasing hormone deficiency (IGD) constitutes a small subset of cases of hypogonadotropic hypogonadism (HH).

IHH is due to deficiency in or insensitivity to gonadotropin-releasing hormone (GnRH), where the function and anatomy of the anterior pituitary is otherwise normal, and secondary causes of HH are not present.

The table in the multiple endocrine neoplasia article lists the genes involved in the various MEN syndromes. Most cases of MEN2 derive from a variation in the "RET proto-oncogene", and are specific for cells of neural crest origin. A database of MEN" implicated RET mutations is maintained by the University of Utah Department of Physiology.

The protein produced by the "RET gene" plays an important role in the TGF-beta (transforming growth factor beta) signaling system. Because the TGF-beta system operates in nervous tissues throughout the body, variations in the RET gene can have effects in nervous tissues throughout the body.

MEN2 generally results from a gain-of-function variant of a "RET gene". Other diseases, such as Hirschsprung disease, result from loss-of-function variants. OMIM # lists the syndromes associated with the RET gene.

Prolactin secretion in the pituitary is normally suppressed by the brain chemical dopamine. Drugs that block the effects of dopamine at the pituitary or deplete dopamine stores in the brain may cause the pituitary to secrete prolactin. These drugs include the major tranquillizers (phenothiazines), trifluoperazine (Stelazine), and haloperidol (Haldol); antipsychotic medications, such as risperidone and quetiapine; metoclopramide (Reglan), domperidone, cisapride used to treat gastro-oesophageal reflux; medication-induced nausea (such as cancer drugs); and, less often, alpha-methyldopa and reserpine, used to control hypertension; and estrogens and TRH. The sleep drug ramelteon (Rozerem) also increases the risk of hyperprolactinaemia. A benzodiazepine analog, etizolam, can also increase the risk of hyperprolactinaemia. In particular, the dopamine antagonists metoclopramide and domperidone are both powerful prolactin stimulators and have been used to stimulate breast milk secretion for decades. However, since prolactin is antagonized by dopamine and the body depends on the two being in balance, the risk of prolactin stimulation is generally present with all drugs that deplete dopamine, either directly or as a rebound effect.

Evidence indicates that the mechanism of hyperpituitarism can originate from genetic disruption causing pituitary tumorigenesis, most pituitary adenomas are monoclonal, which in turn indicates their origin from an event in a single cell. There are three hormones that are oversecreted resulting in the pituitary adenoma: prolactin, adrenocorticotropic hormone (ACTH), and growth hormone (GH). Excess prolactin may result in a prolactinoma Excess GH results in gigantism, the severity of gigantism depends on whether the epiphyseal plate is open. The four most common types of hyperpituitarism are prolactinoma, corticotropinoma (Cushing's disease), somatotropinoma (gigantism), and thyrotropinoma .

The cause of hyperpituitarism in most cases is due to pituitary adenomas. They usually come from the anterior lobe, are functional and secrete the hormone, GH and prolactin.

Carcinomas that metastasize into the pituitary gland are uncommon and typically seen in the elderly, with lung and breast cancers being the most prevalent, In breast cancer patients, metastases to the pituitary gland occur in approximately 6-8% of cases.

Symptomatic pituitary metastases account for only 7% of reported cases. In those who are symptomatic Diabetes insipidus often occurs with rates approximately 29-71%. Other commonly reported symptoms include anterior pituitary dysfunction, visual field defects, headache/pain, and ophthalmoplegia.

Thyroid hormone resistance syndrome is rare, incidence is variously quoted as 1 in 50,000 or 1 in 40,000 live births. More than 1000 individuals have been identified with thyroid hormone resistance, of which 85% had thyroid hormone beta receptor mutation.

Parathyroid cancer occurs in midlife at the same rate in men and women.

Conditions that appear to result in an increased risk of parathyroid cancer include multiple endocrine neoplasia type 1, autosomal dominant familial isolated hyperparathyroidism and hyperparathyroidism-jaw tumor syndrome (which also is hereditary). Parathyroid cancer has also been associated with external radiation exposure, but, most reports describe an association between radiation and the more common parathyroid adenoma.

Hypogonadotropic hypogonadism (HH), also known as secondary or central hypogonadism, as well as gonadotropin-releasing hormone deficiency or gonadotropin deficiency (GD), is a medical condition characterized by hypogonadism due to an impaired secretion of gonadotropins, including follicle-stimulating hormone (FSH) and luteinizing hormone (LH), by the pituitary gland in the brain, and in turn decreased gonadotropin levels and a resultant lack of sex steroid production.

There is only one study that has measured the prevalence (total number of cases in a population) and incidence (annual number of new cases) of hypopituitarism. This study was conducted in Northern Spain and used hospital records in a well-defined population. The study showed that 45.5 people out of 100,000 had been diagnosed with hypopituitarism, with 4.2 new cases per year. 61% were due to tumors of the pituitary gland, 9% due to other types of lesions, and 19% due to other causes; in 11% no cause could be identified.

Recent studies have shown that people with a previous traumatic brain injury, spontaneous subarachnoid hemorrhage (a type of stroke) or radiation therapy involving the head have a higher risk of hypopituitarism. After traumatic brain injury, as much as a quarter have persistent pituitary hormone deficiencies. Many of these people may have subtle or non-specific symptoms that are not linked to pituitary problems but attributed to their previous condition. It is therefore possible that many cases of hypopituitarism remain undiagnosed, and that the annual incidence would rise to 31 per 100,000 annually if people from these risk groups were to be tested.

The most common cause of primary hyperparathyroidism is a sporadic, single parathyroid adenoma resulting from a clonal mutation (~97%). Less common are parathyroid hyperplasia (~2.5%), parathyroid carcinoma (malignant tumor), and adenomas in more than one gland (together ~0.5%).

Primary hyperparathyroidism is also a feature of several familial endocrine disorders: Multiple endocrine neoplasia type 1 and type 2A (MEN type 1 and MEN type 2A), and familial hyperparathyroidism.

Genetic associations include:

In all cases, the disease is idiopathic, but is thought to involve inactivation of tumor suppressor genes (Menin gene in MEN1), or involve gain of function mutations (RET proto-oncogene MEN 2a).

Recently, it was demonstrated that liquidators of the Chernobyl power plant are faced with a substantial risk of primary hyperparathyroidism, possibly caused by radioactive strontium isotopes.

Primary hyperparathyroidism can also result from pregnancy. It is apparently very rare, with only about 110 cases have so far been reported in world literature, but this is probably a considerable underestimate of its actual prevalence in pregnant women.