Male Hypogonadism: Genetics and Family History

Does hypogonadism run in families?

Partly, and it depends which kind. Two genetic causes are well described: Klinefelter syndrome, a chromosome difference that usually arises by chance rather than being passed down from a parent and that causes testicular failure, and single-gene forms of CHH, which can run in families and in which the hypothalamus or pituitary fails to supply the gonadotropin signal to the testes [7][2].

Common genetic variation behaves differently. In 425,097 UK Biobank participants, one study identified 2,571 genome-wide significant associations with testosterone and related sex hormone traits [9], and a second analysis of the same cohort found that most of the SNP-based heritability of testosterone is driven by a massively polygenic background [10]. Hypogonadism is a separate call: symptoms and signs plus consistently low testosterone [4].

The Endocrine Society recommends making the diagnosis only in men with symptoms and signs consistent with testosterone deficiency and unequivocally and consistently low serum testosterone, measured fasting in the morning with an accurate and reliable assay and confirmed by repeating the measurement [4]. The AUA uses a total testosterone below 300 ng/dL as a reasonable cutoff, requires two early-morning measurements on separate occasions, and states that a single low value or symptoms alone are not enough [5]. The Endocrine Society does not recommend screening the general population [4].

Klinefelter syndrome: a chromosome cause

Klinefelter syndrome (47,XXY) appears by name in testosterone prescribing information as a cause of primary hypogonadism, the pattern in which men usually have low testosterone with LH and FSH above the normal range [7].

The Danish Cytogenetic Central Registry gives the clearest numbers. Between 1970 and 2000, 76,526 prenatal examinations on male fetuses identified 163 with a Klinefelter karyotype; standardized for maternal age, that is 153 per 100,000 male fetuses [1]. Postnatally, 696 of 2,480,858 live-born males were diagnosed [1]. The registry also showed how much is missed: only about one fourth of adult men with the karyotype had been identified, and less than 10% of the expected number was diagnosed before puberty [1].

LH and FSH help distinguish primary from secondary hypogonadism: primary hypogonadism, which includes Klinefelter syndrome, usually has low testosterone with high LH and FSH, while secondary hypogonadism has low testosterone with LH and FSH in the normal or low range [4][7].

Kallmann syndrome and congenital hypogonadotropic hypogonadism

CHH is caused by deficient production, secretion or action of GnRH, the hypothalamic hormone that regulates the reproductive axis [2]. About 50% of patients also have a defective sense of smell (anosmia or hyposmia), and that combination is called Kallmann syndrome [2].

The gene list keeps growing. The 2015 European consensus statement counted more than 25 causal genes [2]; a 2019 review counted more than 30 [8]; a 2021 review catalogued 60 genes whose loss-of-function variants can disrupt central control of reproduction [3]. A genetic basis can be defined in almost 50% of cases, although that may not be the complete genetic basis [3].

CHH inheritance resists a simple pattern. Some genes are associated only with normosmic CHH, some only with Kallmann syndrome, and some with either form, even within the same family. More than one variant may contribute, and variability in expressivity and penetrance can make the pattern difficult to predict [3].

Most patients need lifelong treatment, but about 10% to 20% of men recover reproductive function spontaneously, and when fertility is the goal it can be induced with pulsatile GnRH or gonadotropin regimens in most patients [2][8].

What a genetic diagnosis changes about treatment

The threshold does not change. Testosterone products are labeled for replacement therapy in men with primary or hypogonadotropic hypogonadism [7][11], and FDA describes approved testosterone as being for men who lack or have low testosterone together with an associated medical condition; testicular failure from genetic problems is one of its own examples [6]. The current Depo-Testosterone label states that safety and efficacy in men with age-related hypogonadism have not been established, while FDA later requested label updates that included removing that limitation [11][6].

Two things do change.

Fertility. Exogenous androgens can suppress spermatogenesis, and the Testim label lists azoospermia as a possible effect [7][4]. The Endocrine Society recommends against starting testosterone in men who are planning fertility in the near term [4], and the AUA statement is that exogenous testosterone should not be prescribed to men who are currently trying to conceive [5]. In CHH, fertility can usually be induced with pulsatile GnRH or gonadotropin regimens instead [8].

Which drug. Human chorionic gonadotropin is FDA-approved for selected cases of hypogonadotropic hypogonadism secondary to pituitary deficiency in males [12]. Clomiphene is approved only for ovulatory dysfunction in women, so male use is off-label, and enclomiphene is not FDA-approved in any form [13][14].

Klinefelter syndrome and fathering children

Across 37 studies and 1,248 men with Klinefelter syndrome (mean age 30.9), sperm retrieval per testicular sperm extraction cycle succeeded 44% of the time (95% CI 39 to 48), with no difference between micro-TESE and conventional TESE, and 43% of ICSI cycles produced a biochemical pregnancy [15]. Age, testis volume, FSH, LH and testosterone at enrolment did not predict retrieval [15]. There were not enough data to judge whether prior testosterone treatment affected retrieval [15].

Does family history change testing?

For a man with a family history, the diagnosis still requires symptoms and signs plus consistently low fasting morning testosterone confirmed by repeat testing [4][5]. If total testosterone is near the lower limit of normal, or a condition alters sex hormone-binding globulin, the Endocrine Society recommends free testosterone by equilibrium dialysis or an accurate formula [4].

A known family variant may not produce the same presentation in every relative: the CHH review describes variable expressivity and penetrance, and notes that more than one gene or variant can contribute [3].

Is the cardiovascular question different when the cause is genetic?

The available cardiovascular results come from men with hypogonadism and cardiovascular risk who used transdermal testosterone gel; they do not establish whether cardiovascular outcomes differ by genetic cause [16]. In TRAVERSE, 5,246 men aged 45 to 80 with symptoms of hypogonadism, two fasting testosterone levels below 300 ng/dL, and existing cardiovascular disease or high risk received 1.62% testosterone gel or placebo; a first major cardiovascular event occurred in 7.0% versus 7.3% (hazard ratio 0.96, 95% CI 0.78 to 1.17), meeting noninferiority [16]. In the Testim label's tabulation of the trial, atrial fibrillation (3.5% versus 2.4%) and acute kidney injury (2.3% versus 1.5%) were more frequent with testosterone [7].