In an Estonian study of 866 men with infertility, those with at least 24 GGN repeats in the androgen receptor gene had a median total sperm count about 26% lower than those with 22 repeats or fewer. The researchers found no significant association between repeat length and circulating reproductive hormone levels.
Why do men who share similar environments have different sperm counts? Smoking, obesity, stress and exposure to endocrine-disrupting chemicals are among the factors that may affect sperm production. A team in Estonia investigated another possibility: genetic variation in the receptor through which testosterone acts. Their paper appeared online June 23, 2026, in the Asian Journal of Andrology and in its November issue.
Normal testosterone levels can coexist with a low sperm count
Testosterone plays an important role in male reproduction and sperm production. A normal blood level alone cannot establish that sperm production is normal. Testosterone acts by binding to androgen receptors inside cells. These proteins receive the hormonal signal and regulate gene expression.
The androgen receptor (AR) gene contains stretches of repeated DNA known as CAG and GGN repeats. The number of repeats varies between individuals. The researchers examined whether repeat length was related to sperm count in men receiving care for infertility.
What the 26% difference describes
Men with at least 24 GGN repeats had a median total count of 13.5 million sperm per ejaculate, compared with 18.2 million in men with 22 repeats or fewer. The difference of about 4.7 million amounted to roughly 26% of the latter group's median.
The pattern was more pronounced when both repeat stretches were long. Men with at least 24 GGN repeats and at least 25 CAG repeats accounted for 6.8% of patients. Their median sperm concentration was 3.5 million per milliliter. Concentration and total count per ejaculate are different measurements.
These findings suggest that inherited differences in the receptor might matter alongside the amount of hormone produced. The figures are group medians. They cannot predict an individual's fertility or establish that every man with a long repeat tract will have a low count.
Blood hormone levels showed no clear association
Repeat length was not significantly associated with testosterone, follicle-stimulating hormone (FSH) or luteinizing hormone (LH). Sperm production may depend partly on how cells respond to a signal even when enough testosterone is present. The researchers did not directly demonstrate a change in receptor function, and the mechanism linking repeats to sperm count requires further study.
A meta-analysis of 1,843 men
The investigators also analyzed data from 1,843 men, including a cohort of young men in the Baltic region. The association between GGN repeat length and sperm count was statistically significant (P = 0.044). This suggests the pattern observed among infertility patients may also be seen in another population.
An association alone cannot establish that the genetic variant caused a lower count. Testicular function, hormonal regulation, metabolic health, lifestyle and environmental exposures can all influence sperm production. Researchers still need to establish whether the association is similar across populations.
Could repeat testing help diagnose male infertility?
Semen analysis remains central to assessment. It measures concentration, total count, motility and morphology. Hormone or genetic testing may be appropriate in selected circumstances. For some men with severe impairment of sperm production, clinicians may recommend a karyotype or Y-chromosome microdeletion testing.
The AR finding provides a lead for understanding otherwise unexplained infertility. GGN repeat testing is not an established standard diagnostic test, and repeat length cannot reliably predict natural conception or IVF success. Before clinical use, the findings need replication in diverse populations and studies of pregnancy and birth outcomes as well as sperm production.
The question extends beyond how much hormone a man produces to how his cells receive its signal. A low sperm count may sometimes reflect genetic differences that lifestyle or circulating hormone levels alone cannot explain.
Source: “The long (GGN)n repeat tract in the androgen receptor gene exerts a negative effect on quantitative sperm parameters.” Asian Journal of Andrology, 28(6), 947–953. Published online June 23, 2026. DOI: 10.4103/aja202612. Men with an abnormal semen analysis can discuss individual evaluation with a urologist or reproductive specialist. The illustration depicts a fictional person.
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