Reversal of symptoms have been reported in between 15% to 22% of cases. The causes of this reversal are still under investigation but have been reported in both males and females.

Reversal appears to be associated with 14 of the known gene defects linked to KS/CHH. The study suggests no obvious gene defect showing a tendency to allow reversal. There is a suggestion that the TAC3 and TACR3 mutations might allow for a slightly higher chance of reversal, but the numbers involved are too low to confirm this. The ANOS1 mutations appear to be least likely to allow reversal with to date only one recorded instance in medical literature. Even male patients who previous had micro-phallus or cryptorchidism have been shown to undergo reversal of symptoms.

The reversal might not be permanent and remission can occur at any stage; the paper suggests that this could be linked to stress levels. The paper highlighted a reversal case that went into remission but subsequently achieved reversal again, strongly suggesting an environmental link.

Reversal cases have been seen in cases of both KS and normosmic CHH but appear to be less common in cases of KS (where the sense of smell is also affected). A paper published in 2016 agreed with the theory that there is a strong environmental or epigenetic link to the reversal cases. The precise mechanism of reversal is unclear and is an area of active research.

Reversal would be apparent if testicular development was seen in men while on testosterone therapy alone or in women who menstruate or achieved pregnancy while on no treatment. To date there have been no recorded cases of the reversal of anosmia found in Kallmann syndrome cases.

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 epidemiology of Kallmann's is not well understood. Individual studies include a 1986 report reviewing medical records in the Sardinian army found a prevalence of 1 in 86,000 men and a 2011 report from Finland found a prevalence of 1:30,000 for males and 1:125,000 for females.

There is 4 to 5:1 ratio of men to women among all people with Kallmann syndrome; in familial Kallmann the ratio is lower, at 2.5 to 1.

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 increasing evidence that the harmful products of tobacco smoking may damage the testicles and kill sperm, but their effect on male fertility is not clear. Some governments require manufacturers to put warnings on packets. Smoking tobacco increases intake of cadmium, because the tobacco plant absorbs the metal. Cadmium, being chemically similar to zinc, may replace zinc in the DNA polymerase, which plays a critical role in sperm production. Zinc replaced by cadmium in DNA polymerase can be particularly damaging to the testes.

Isolated hypogonadotropic hypogonadism (IHH), also called idiopathic or congenital hypogonadotropic hypogonadism (CHH), as well as isolated or congenital gonadotropin-releasing hormone deficiency (IGD), is a condition which results in 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 is otherwise normal and secondary causes of HH are not present.

Pre-testicular factors refer to conditions that impede adequate support of the testes and include situations of poor hormonal support and poor general health including:

- Hypogonadotropic hypogonadism due to various causes

- Obesity increases the risk of hypogonadotropic hypogonadism. Animal models indicate that obesity causes leptin insensitivity in the hypothalamus, leading to decreased Kiss1 expression, which, in turn, alters the release of gonadotropin-releasing hormone (GnRH).

- Undiagnosed and untreated coeliac disease (CD). Coeliac men may have reversible infertility. Nevertheless, CD can present with several non-gastrointestinal symptoms that can involve nearly any organ system, even in the absence of gastrointestinal symptoms. Thus, the diagnosis may be missed, leading to a risk of long-term complications. In men, CD can reduce semen quality and cause immature secondary sex characteristics, hypogonadism and hyperprolactinaemia, which causes impotence and loss of libido. The giving of gluten free diet and correction of deficient dietary elements can lead to a return of fertility. It is likely that an effective evaluation for infertility would best include assessment for underlying celiac disease, both in men and women.

- Drugs, alcohol

- Strenuous riding (bicycle riding, horseback riding)

- Medications, including those that affect spermatogenesis such as chemotherapy, anabolic steroids, cimetidine, spironolactone; those that decrease FSH levels such as phenytoin; those that decrease sperm motility such as sulfasalazine and nitrofurantoin

- Genetic abnormalities such as a Robertsonian translocation

Based on its cause, the type of hypogonadotropic hypogonadism (HH) may be classified as either "primary" or "secondary".

"Primary" HH, also called isolated hypogonadotropic hypogonadism, is responsible for only a small subset of cases of HH, and is characterized by an otherwise normal function and anatomy of the hypothalamus and anterior pituitary. It is caused by congenital disorders such as Kallmann syndrome, CHARGE syndrome, and gonadotropin-releasing hormone insensitivity.

"Secondary" HH, also known as acquired or syndromic HH, is far more common than primary HH, and responsible for most cases of the condition. It has a multitude of different causes, including brain or pituitary tumors, pituitary apoplexy, head trauma, ingestion of certain drugs, and certain systemic diseases and syndromes.

Primary and secondary HH can also be attributed to a genetic trait inherited from the biologic parents. For example, the male mutations of the GnRH coding gene could result in HH. Hormone replacement can be used to initiate puberty and continue if the gene mutation occurs in the gene coding for the hormone. Chromosomal mutations tend to affect the androgen production rather than the HPG axis.

Gonadotropin-releasing hormone (GnRH) insensitivity is a rare autosomal recessive genetic and endocrine syndrome which is characterized by inactivating mutations of the gonadotropin-releasing hormone receptor (GnRHR) and thus an insensitivity of the receptor to gonadotropin-releasing hormone (GnRH), resulting in a partial or complete loss of the ability of the gonads to synthesize the sex hormones. The condition manifests itself as isolated hypogonadotropic hypogonadism (IHH), presenting with symptoms such as delayed, reduced, or absent puberty, low or complete lack of libido, and infertility, and is the predominant cause of IHH when it does not present alongside anosmia.

XX gonadal dysgenesis is related to the Swyer syndrome inasmuch as both conditions have the same phenotype and clinical issues; however in Swyer syndrome the karyotype is 46,XY, and thus gonadectomy is recommended.

In Turner syndrome there is a demonstrable abnormality in or absence of one of the sex chromosomes that is the cause of the development of gonadal dysgenesis. In contrast XX gonadal dysgenesis has a normal female chromosome situation.

Another type of XX gonadal dysgenesis is known as 46,XX gonadal dysgenesis epibulbar dermoid, which follows the similar symptoms as the regular syndrome, though it also shows signs of epibulbar dermoid (eye disorder). It has been suggested to be a new type of syndrome.

One of the main characteristics of this disorder is adrenal insufficiency, which is a reduction in adrenal gland function resulting from incomplete development of the gland's outer layer (the adrenal cortex). Adrenal insufficiency typically begins in infancy or in childhood and can cause vomiting, difficulty with feeding, dehydration, extremely low blood sugar (hypoglycemia), low sodium levels, and shock. However, adult-onset cases have also been described. See also Addison's Disease.

Affected males may also lack male sex hormones, which leads to underdeveloped reproductive tissues, undescended testicles (cryptorchidism), delayed puberty, and an inability to father children (infertility). These characteristics are known as hypogonadotropic hypogonadism. Females are rarely affected by this disorder, but a few cases have been reported of adrenal insufficiency or a lack of female sex hormones, resulting in underdeveloped reproductive tissues, delayed puberty, and an absence of menstruation.

The fertile eunuch syndrome is a cause of hypogonadotropic hypogonadism caused by a luteinizing hormone deficiency. It is characterized by hypogonadism with spermatogenesis. Pasqualini and Bur published the first case of eunuchoidism with preserved spermatogenesis in 1950 in la Revista de la Asociación Médica Argentina.

The hypoandrogenism with spermatogenesis syndrome included: (a) eunuchoidism, (b) testis with normal spermatogenesis and full volume, with mature spermatozoids in a high proportion of seminiferous tubes and undifferentiated and immature Leydig cells (c) full functional compensation through the administration of chorionic gonadotropin hormone, while hCG is administered (d) total urinary gonadotrophins within normal limits (e) this definition implies the normal activity of the pituitary and the absence of congenital malformations in general. In describing five other similar cases in 1953, Mc Cullagh & al coined the term fertile eunuch introducing it in the English literature. Unfortunately, this term is incorrect and should not be employed. Indeed, these patients are not really eunuchs. Moreover, as it will be explained later, they are not usually fertile if not treated.

A first step in the understanding of the physiopathology of Pasqualini syndrome was the absence of Lutheinizing Hormone (LH) in plasma and urine of patients. The second breakthrough was the functional and genetic studies that validated the hypothesis of a functional deficit of LH in these men. Inactivating LH mutations will then also be described in some women. Different groups demonstrated in these cases a LH with varying degrees of immunological activity but biologically inactive in most of the patients, due to one or more inactivating mutations in the LHB gene. Finally, the full comprehension of Pasqualini syndrome allowed to reverse the hypoandrogenic phenotype and to restore fertility in these patients through the use of chorionic gonadotropin and the modern in-vitro fertility techniques

Mutations in the "NR0B1" gene located on the X chromosome (Xp21.3-p21.2) cause X-linked adrenal hypoplasia congenita. The "NR0B1" gene provides instructions to make a transcription factor protein called DAX1 that helps control the activity of certain genes. When the "NR0B1" gene is deleted or mutated, the activity of certain genes is not properly controlled. This leads to problems with the development of the adrenal glands, two structures in the brain (the hypothalamus and pituitary gland), and reproductive tissues (the ovaries or testes). These tissues are important for the production of many hormones that control various functions in the body. When these hormones are not present in the correct amounts, the signs and symptoms of adrenal insufficiency and hypogonadotropic hypogonadism can result. This condition is inherited in an X-linked recessive pattern.

In 1951, Perrault reported the association of gonadal dysgenesis and deafness, now called Perrault syndrome.

Treatment may consist of hormone replacement therapy with androgens in either sex. Alternatively, gonadotropin-releasing hormone (GnRH)/GnRH agonists or gonadotropins may be given (in the case of "hypogonadotropic" hypoandrogenism). The Food and Drug Administration (FDA) stated in 2015 that neither the benefits nor the safety of testosterone have been established for low testosterone levels due to aging. The FDA has required that testosterone pharmaceutical labels include warning information about the possibility of an increased risk of heart attacks and stroke.

Androgen deficiency is not usually checked for diagnosis in healthy women.

Hypogonadism can involve just hormone production or just fertility, but most commonly involves both.

- Examples of hypogonadism that affect hormone production more than fertility are hypopituitarism and Kallmann syndrome; in both cases, fertility is reduced until hormones are replaced but can be achieved solely with hormone replacement.

- Examples of hypogonadism that affect fertility more than hormone production are Klinefelter syndrome and Kartagener syndrome.

Deficiency of sex hormones can result in defective primary or secondary sexual development, or withdrawal effects (e.g., premature menopause) in adults. Defective egg or sperm development results in infertility. The term hypogonadism usually means permanent rather than transient or reversible defects, and usually implies deficiency of reproductive hormones, with or without fertility defects. The term is less commonly used for infertility without hormone deficiency. There are many possible types of hypogonadism and several ways to categorize them. Hypogonadism is also categorized by endocrinologists by the level of the reproductive system that is defective. Physicians measure gonadotropins (LH and FSH) to distinguish primary from secondary hypogonadism. In primary hypogonadism the LH and/or FSH are usually elevated, meaning the problem is in the testicles, whereas in secondary hypogonadism, both are normal or low, suggesting the problem is in the brain.

As the syndrome is due to a chromosomal non-disjunction event, the recurrence risk is not high compared to the general population. There has been no evidence found that indicates non-disjunction occurs more often in a particular family.

In 2012, a 5-generation Dutch family consisting of 7 males and 7 females with Wilson-Turner Syndrome. These individuals had some characteristics that differed from the stated phenotype mentioned by Wilson. These individuals have a larger stature, head, and chin, in addition to coarse facial features. Unlike the females in Wilson's study, these females shown signs of being affected, although less severe than their male counterparts. None of the men could live on their own. Studies verified that the phenotype of the disorder range on a large scale and can affect everyone differently. This research group also used next-generation sequencing of the X chromosome exome to identify the HDAC8 gene mutation

There is also ongoing research to determine the cause of the decreased or low androgen levels. It is studying the possible disturbance of the hypothalamic-pituitary-gonadal axis because of the low levels of androgen are combined with normal levels of FSH and LH.

Pendred syndrome is a genetic disorder leading to congenital bilateral (both sides) sensorineural hearing loss and goitre with euthyroid or mild hypothyroidism (decreased thyroid gland function). There is no specific treatment, other than supportive measures for the hearing loss and thyroid hormone supplementation in case of hypothyroidism. It is named after Dr Vaughan Pendred (1869–1946), the English doctor who first described the condition in an Irish family living in Durham in 1896. It accounts for 7.5% to 15% of all cases of congenital deafness.

Crandall syndrome is a very rare congenital disorder characterised by progressive sensorineural hearing loss, hair loss associated with pili torti, and hypogonadism demonstrated through low levels of luteinising hormone and growth hormone. It is thought to be an autosomal recessive disorder closely related to Björnstad syndrome which presents similarly but without hypogonadism.

The condition was first reported by B. F. Crandall in 1973.

Unlike Borjeson-Forssman-Lehmann syndrome, a disorder that was determined to be very similar to WTS, the individuals with Wilson–Turner syndrome do not develop cataracts or hypermetropia later in life. By far, the most debilitating part of this disorder is intellectual disability. Many of the other symptoms are more easily managed through hormone treatment, proper diet and exercise, and speech therapy.

Pendred syndrome is inherited in an autosomal recessive manner, meaning that one would need to inherit an abnormal gene from each parent to develop the condition. This also means that a sibling of a patient with Pendred syndrome has a 25% chance of also having the condition if the parents are unaffected carriers.

It has been linked to mutations in the "PDS" gene, which codes for the "pendrin" protein (solute carrier family 26, member 4, SLC26A4). The gene is located on the long arm of chromosome 7 (7q31). Mutations in the same gene also cause enlarged vestibular aqueduct syndrome (EVA or EVAS), another congenital cause of deafness; specific mutations are more likely to cause EVAS, while others are more linked with Pendred syndrome.

Thyroid dyshormonogenesis (or dyshormogenetic goiter) is a rare condition due to genetic defects in the synthesis of thyroid hormones.

Patients develop hypothyroidism with a goitre.either deficiency of thyroid enzymes or inability to concentrate or ineffective binding