It is normally difficult to distinguish a case of KS / HH from a straightforward constitutional delay of puberty. However, if puberty has not started by either age 14 (girls) or 15 (boys) and one or more of the non-reproductie features mentioned belowe is present then a referral to reproductive endocrinologist might be advisable.

The features of Kallmann syndrome (KS) and other forms of hypogonadotropic hypogonadism (HH) can be split into two different categories; "reproductive" and "non reproductive".

The exact genetic nature of each particular case of KS / HH will determine which, if any, of the non-reproductive features will occur. The severity of the symptoms will also vary from case to case. Even family members will not show the same range or severity of symptoms.

KS / HH is most often present from birth but adult onset versions are found in both males and females. The hypothalamic-pituitary-gonadal axis (HPG axis) functions normally at birth and well into adult life giving normal puberty and normal reproductive function. The HPG axis then either fails totally or is reduced to a very low level of GnRH release, in adult life with no obvious cause such as a pituitary tumour. This will lead to a fall in testosterone or oestrogen levels and infertility.

Functional hypothalamic amenorrhoea is seen in females where the HPG axis is suppressed in response to physical or psychological stress or malnutrition. It is reversible with the removal of the stressor.

Some cases of KS / HH appear to reverse during adult life where the HPG axis resumes its normal function and GnRH, LH, and FSH levels return to normal levels. This occurs in an estimated 10 to 20% of cases, primarily normosmic CHH cases rather than KS cases and only found in patients who have undergone some form of testosterone replacement therapy.

It is only normally discovered when testicular volume increases while on testosterone treatment alone and testosterone levels return to normal when treatment is stopped. This type of KS / HH rarely occurs in cases where males have had a history of un-descended testes.

Affected individuals with KS and other forms of HH are almost invariably born with normal sexual differentiation; i.e., they are physically male or female. This is due to the human chorionic gonadotrophin (hCG) produced by placenta at approximately 12 to 20 weeks gestation (pregnancy) which is normally unaffected by having KS or CHH.

People with KS / HH lack the surge of GnRH, LH, and FSH that normally occurs between birth and six months of age. This surge is particularly important in infant boys as it helps with testicular descent into the scrotum. The surge of GnRH/LH/FSH in non KS/HH children gives detectable levels of testosterone in boys and oestrogen & progesterone in girls. The lack of this surge can sometimes be used as a diagnostic tool if KS / HH is suspected in a newborn boy, but is not normally distinct enough for diagnosis in girls.

The symptoms of Leydig cell hypoplasia include pseudohermaphroditism (i.e., feminized, ambiguous, or relatively mildly underdeveloped (e.g., micropenis, severe hypospadias, and/or cryptorchidism (undescended testes)) external genitalia), a female gender identity or gender variance, hypergonadotropic hypogonadism (hypogonadism despite high levels of gonadotropins), delayed, impaired, or fully absent puberty with an associated reduction in or complete lack of development of secondary sexual characteristics (sexual infantilism), impaired fertility or complete sterility, tall stature (due to delayed epiphyseal closure), eunuchoid skeletal proportions, delayed or absent bone maturation, and osteoporosis.

Congenital hypogonadotropic hypogonadism presents as hypogonadism, e.g., reduced or absent puberty, low libido, infertility, etc. due to an impaired release of the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and a resultant lack of sex steroid and peptides production by the gonads.

In Kallmann syndrome, a variable non-reproductive phenotype occurs with anosmia (loss of the sense of smell) including sensorineural deafness, coloboma, bimanual synkinesis, craniofacial abnormalities, and/or renal agenesis.

Leydig cell hypoplasia (or aplasia) (LCH), also known as Leydig cell agenesis, is a rare autosomal recessive genetic and endocrine syndrome affecting an estimated 1 in 1,000,000 genetic males. It is characterized by an inability of the body to respond to luteinizing hormone (LH), a gonadotropin which is normally responsible for signaling Leydig cells of the testicles to produce testosterone and other androgen sex hormones. The condition manifests itself as pseudohermaphroditism (partially or fully underdeveloped genitalia), hypergonadotropic hypogonadism (decreased or lack of production of sex steroids by the gonads despite high circulating levels of gonadotropins), reduced or absent puberty (lack of development of secondary sexual characteristics, resulting in sexual infantilism if left untreated), and infertility.

Leydig cell hypoplasia does not occur in biological females as they do not have either Leydig cells or testicles. However, the cause of the condition in males, luteinizing hormone insensitivity, does affect females, and because LH plays a role in the female reproductive system, it can result in primary amenorrhea or oligomenorrhea (absent or reduced menstruation), infertility due to anovulation, and ovarian cysts.

A related condition is follicle-stimulating hormone (FSH) insensitivity, which presents with similar symptoms to those of Leydig cell hypoplasia but with the symptoms in the respective sexes reversed (i.e., hypogonadism and sexual infantilism in females and merely problems with fertility in males). Despite their similar causes, FSH insensitivity is considerably less common in comparison to LH insensitivity.

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.

As babies and children, XXY males may have weaker muscles and reduced strength. As they grow older, they tend to become taller than average. They may have less muscle control and coordination than other boys of their age.

During puberty, the physical traits of the syndrome become more evident; because these boys do not produce as much testosterone as other boys, they have a less muscular body, less facial and body hair, and broader hips. As teens, XXY males may develop breast tissue and also have weaker bones, and a lower energy level than other males.

By adulthood, XXY males look similar to males without the condition, although they are often taller. In adults, possible characteristics vary widely and include little to no sign of affectedness, a , youthful build and facial appearance, or a rounded body type with some degree of gynecomastia (increased breast tissue). Gynecomastia is present to some extent in about a third of affected individuals, a slightly higher percentage than in the XY population. About 10% of XXY males have gynecomastia noticeable enough that they may choose to have cosmetic surgery.

Affected males are often infertile, or may have reduced fertility. Advanced reproductive assistance is sometimes possible.

The term "hypogonadism" in XXY symptoms is often misinterpreted to mean "small testicles" when it means decreased testicular hormone/endocrine function. Because of this (primary) hypogonadism, individuals will often have a low serum testosterone level but high serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels. Despite this misunderstanding of the term, however, it is true that XXY men may also have microorchidism (i.e., small testicles).

The testicle size of affected males are usually less than 2 cm in length (and always shorter than 3.5 cm), 1 cm in width and 4 ml in volume.

XXY males are also more likely than other men to have certain health problems that typically affect females, such as autoimmune disorders, breast cancer, venous thromboembolic disease, and osteoporosis. In contrast to these potentially increased risks, it is currently thought that rare X-linked recessive conditions occur less frequently in XXY males than in normal XY males, since these conditions are transmitted by genes on the X chromosome, and people with two X chromosomes are typically only carriers rather than affected by these X-linked recessive conditions.

This syndrome is inherited as an autosomal disease. It affects both males and females but the phenotype differs. In both sexes sensorineural deafness occurs but in females ovarian dysgenesis also occurs.

XX gonadal dysgenesis is a type of female hypogonadism in which no functional ovaries are present to induce puberty in an otherwise normal girl whose karyotype is found to be 46,XX. With nonfunctional "streak" ovaries she is low in estrogen levels (hypoestrogenic) and has high levels of FSH and LH. Estrogen and progesterone therapy is usually then commenced.

The term “pure gonadal dysgenesis” (PGD) has been used to distinguish a group of patients from gonadal dysgenesis related to Turner syndrome. In the latter a distinct chromosomal aberration is present, while in PGD the chromosomal constellation is either 46,XX or 46,XY. Thus XX gonadal dysgenesis is also referred to as "PGD, 46 XX", and XY gonadal dysgenesis as "PGD, 46,XY" or Swyer syndrome. Patients with PGD have a normal chromosomal constellation but may have localized genetic alterations.

Some degree of language learning or reading impairment may be present, and neuropsychological testing often reveals deficits in executive functions, although these deficits can often be overcome through early intervention. There may also be delays in motor development which can be addressed through occupational therapy and physical therapy. XXY males may sit up, crawl, and walk later than other infants; they may also struggle in school, both academically and with sports.

Of the abnormal conditions associated with micropenis, most are conditions of reduced prenatal androgen production or effect, such as abnormal testicular development (testicular dysgenesis), Klinefelter syndrome, Leydig cell hypoplasia), specific defects of testosterone or dihydrotestosterone synthesis (17,20-lyase deficiency, 5α-reductase deficiency), androgen insensitivity syndromes, inadequate pituitary stimulation (gonadotropin deficiency), and other forms of congenital hypogonadism. Micropenis can also occur as part of many genetic malformation syndromes that do not involve the sex chromosomes. It is sometimes a sign of congenital growth-hormone deficiency or congenital hypopituitarism. Several homeobox genes affect penis and digit size without detectable hormone abnormalities.

In addition, in utero exposure to some estrogen based fertility drugs like diethylstilbestrol (DES) has been linked to genital abnormalities and/or a smaller than normal penis.

After evaluation to detect any of the conditions described above, micropenis can often be treated in infancy with injections of various hormones, such as human chorionic gonadotropin and testosterone.

Most eight- to fourteen-year-old boys referred for micropenis do not have the micropenis condition. Such concerns are usually explained by one of the following:

- a penis concealed in suprapubic fat (extra fat around the mons pubis)

- a large body and frame for which a prepubertal penis simply appears too small

- delayed puberty with every reason to expect good future growth

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.

The most notable features of Wilson-Turner Syndrome are intellectual disability, obesity, hypogonadism, gynecomastia, and distinct facial features. All of the symptoms are chronic. Affected females are known to have less severe signs and symptoms than males. Female carriers of the disorder may have none or mild symptoms.

- Intellectual Disability is the limitation in an individual's mental functioning and skills. Patients of Wilson-Turner Syndrome have mental disability generally ranging from mild to severe, more frequently on the former. This symptom often coincides with delay in speech development and the occurrence of mood swings. Most males were noted to have a quiet and a cheerful disposition. However, individuals who displayed aggression and became easily upset were also seen. Children will display a delay in speech development often combined with excessive drooling and low voice tone. Some of the studied male patients had speech impairment ranging from little or no speech to minor stuttering.

- Obesity is the accumulation of excess fat on the body. Individuals with Wilson-Turner Syndrome are characterized to have truncal obesity, meaning the fat has accumulated in one's middle. Truncal obesity is often related to heart disease, kidney disease, and lowered blood immune system. Truncal obesity in this disorder becomes more apparent around the age of puberty.

- Tapered fingers is when one end of the finger is diminished in thickness, causing the ends of the fingers to appear pointed. This deformity is not debilitating in any particular manner. In addition to tapered fingers, both hands and feet tend to be small. Some males were observed to have pes planus, also known as flat feet.

- Hypogonadism is a condition in which the gonads have a decrease in function. This condition may result from the lack of sex hormone synthesis, such as androgen and estrogen. Hormones produced by the gonads may also decrease. Hypogonadism also influences the onset of other conditions of the Wilson-Turner Syndrome, such as gynecomastia and decreased testes size in males. It can also cause short stature in men and women. In addition to little genital development, pubic and body hair are scant.

- Some of the facial features that are associated with Wilson-Turner Syndrome include small head circumference, high forehead, prominent ears, and nose with a flattened bridge. There have been cases of a moderately high palate. Low muscle tone and subcutaneous swelling in facial tissue has also been noted. Thick eyebrows are also common. However, there has been reported cases where individuals had none of the mentioned facial features, which shows phenotypic abnormalities have possible environmental influences.

- Gynecomastia is a non-cancerous increase in male breast tissue. It is believed that disturbances in the endocrine system leads to an increase in estrogen and androgen hormones lead to the development of gynecomastia. A key feature of gynecomastia is a rubbery or firm glandular subcutaneous chest tissue that is palpated under the areola of the nipple, instead of the soft fatty tissue. There can also be in increase in diameter of the areola asymmetry in the chest tissue. The breast enlargement can occur in one or both side. Similar to truncal obesity, gynecomastia becomes apparent around the age of puberty.

In medicine, Infantilism is an obsolete term for various, often unrelated disorders of human development, up to developmental disability, which consist of retention of the physical and/or psychological characteristics of early developmental stages (infant, child) into a relatively advanced age.

Various types of infantilism were recognized, lumped together in the above superficial description. With better understanding of the endocrine system and genetic disorders, various disorders which included the word "infantilism" received other names. For example, Brissaud's infantilism, described by Édouard Brissaud in 1907 is now known as myxedema (a form of hypothyroidism); "intestinal infantilism" of Christian Archibald Herter is called coeliac disease. The Turner syndrome was described as "a syndrome of infantilism" by Henry Turner himself.

Terms such as "genital infantilism" (infantilism in development of genitals, hypogenitalism), or "sexual infantilism" (lack of sexual development after expected puberty or delayed puberty) may still be seen, and are considered to be synonyms of hypogonadism. "Somatic infantilism" refers to infantilism of overall bodily development. Speech infantilism is a speech disorder.

Similarly to some other medical terms (cretinism, idiotism), "infantilism"/"infantile" may be used pejoratively (synonymous to "immature").

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.

X-linked adrenal hypoplasia congenita is a genetic disorder that mainly affects males. It involves many endocrine tissues in the body, especially the adrenal glands.

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

Examples of symptoms of hypogonadism with underdevelopment of the Gonads (testicles and ovaries) include delayed, reduced, or absent puberty, low libido, and infertility.

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.

Examples of symptoms of hypogonadism include delayed, reduced, or absent puberty, low libido, and infertility.

Follicle-stimulating hormone (FSH) insensitivity, or ovarian insensitivity to FSH in females, also referable to as ovarian follicle hypoplasia or granulosa cell hypoplasia in females, is a rare autosomal recessive genetic and endocrine syndrome affecting both females and males, with the former presenting with much greater severity of symptomatology. It is characterized by a resistance or complete insensitivity to the effects of follicle-stimulating hormone (FSH), a gonadotropin which is normally responsible for the stimulation of estrogen production by the ovaries in females and maintenance of fertility in both sexes. The condition manifests itself as hypergonadotropic hypogonadism (decreased or lack of production of sex steroids by the gonads despite high circulating levels of gonadotropins), reduced or absent puberty (lack of development of secondary sexual characteristics, resulting in sexual infantilism if left untreated), amenorrhea (lack of menstruation), and infertility in females, whereas males present merely with varying degrees of infertility and associated symptoms (e.g., decreased sperm production).

A related condition is luteinizing hormone (LH) insensitivity (termed Leydig cell hypoplasia when it occurs in males), which presents with similar symptoms to those of FSH insensitivity but with the symptoms in the respective sexes reversed (i.e., hypogonadism and sexual infantilism in males and merely problems with fertility in females); however, males also present with feminized or ambiguous genitalia (also known as pseudohermaphroditism), whereas ambiguous genitalia does not occur in females with FSH insensitivity. Despite their similar causes, LH insensitivity is considerably more common in comparison to FSH insensitivity.

Micropenis is an unusually small penis. A common criterion is a dorsal (measured on top) erect penile length of at least 2.5 standard deviations smaller than the mean human penis size, or smaller than about for an adult when compared with an average erection of . The condition is usually recognized shortly after birth. The term is most often used medically when the rest of the penis, scrotum, and perineum are without ambiguity, such as hypospadias. Micropenis occurs in about 0.6% of males.

Hypergonadotropic hypogonadism (HH), also known as primary or peripheral/gonadal hypogonadism, is a condition which is characterized by hypogonadism due to an impaired response of the gonads to the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and in turn a lack of sex steroid production and elevated gonadotropin levels (as an attempt of compensation by the body). HH may present as either "congenital" or "acquired", but the majority of cases are of the former nature.

Women with hypogonadism do not begin menstruating and it may affect their height and breast development. Onset in women after puberty causes cessation of menstruation, lowered libido, loss of body hair and hot flashes. In boys it causes impaired muscle and beard development and reduced height. In men it can cause reduced body hair and beard, enlarged breasts, loss of muscle, and sexual difficulties. A brain tumor (central hypogonadism) may involve headaches, impaired vision, milky discharge from the breast and symptoms caused by other hormone problems.

The symptoms of hypogonadotrophic hypogonadism, a subtype of hypogonadism, include late, incomplete or lack of development at puberty, and sometimes short stature or the inability to smell; in females, a lack of breasts and menstrual periods, and in males a lack of sexual development, e.g., facial hair, penis and testes enlargement, deepening voice.