rs2414095 — CYP19A1

CYP19A1 rs2414095 — An Intronic Aromatase Variant That Modulates Estradiol and FSH

Aromatase¹¹ Aromatase
encoded by CYP19A1; the enzyme that catalyzes the irreversible conversion of androgens (testosterone, androstenedione) to estrogens (estradiol, estrone) — the rate-limiting step in estrogen biosynthesis is expressed in the gonads, adipose tissue, bone, placenta, breast, and brain. In men, testicular aromatase converts a fraction of circulating testosterone into estradiol, which then feeds back on the hypothalamic–pituitary axis²² hypothalamic–pituitary axis
the signaling cascade where the hypothalamus releases GnRH → pituitary releases FSH and LH → gonads produce sex hormones; estrogen provides negative feedback to suppress FSH and LH release to modulate FSH and LH release. In women, aromatase in granulosa cells is the principal source of ovarian estradiol throughout reproductive life. The rs2414095 variant, located in intron 3 of CYP19A1, influences aromatase expression levels, with the minor A allele associated with reduced estradiol and elevated FSH across multiple independent Asian populations.

The Mechanism

CYP19A1 is located on chromosome 15q21.2 on the minus strand. Intron 3 of CYP19A1 contains regulatory elements governing tissue-specific expression: the gene uses multiple tissue-specific promoters directing aromatase expression in the gonads, adipose tissue, bone, and brain. The rs2414095 A allele likely affects one or more of these regulatory elements, reducing the efficiency of CYP19A1 transcription and, consequently, total aromatase enzyme production.

Lower aromatase activity in the testis means less testosterone is converted to estradiol. In men, estradiol normally inhibits gonadotropin-releasing hormone (GnRH)³³ gonadotropin-releasing hormone (GnRH)
released from the hypothalamus; triggers pituitary FSH and LH release; its pulsatile secretion drives the reproductive axis and FSH release via negative feedback on the pituitary. When this estradiol feedback is reduced, FSH rises — stimulating Sertoli cells more strongly and potentially driving higher sperm production. This mechanistic chain — A allele → lower estradiol → less estrogen feedback → higher FSH → more gonadotropin stimulation of spermatogenesis — is consistent with the GWAS and replication findings described below.

For women, the same reduced aromatase activity in granulosa cells may influence the estrogen environment of the developing follicle, potentially affecting ovarian reserve dynamics and the hormonal milieu of the follicular phase.

The Evidence

The primary discovery came from a genome-wide association study of 3,495 healthy Chinese men⁴⁴ genome-wide association study of 3,495 healthy Chinese men
Chen et al. Journal of Medical Genetics, 2013. Conducted in two stages (1,999 discovery + 1,496 confirmation), this was the first GWAS to report genetic determinants of FSH and LH. The rs2414095 A allele showed exceptionally strong associations with both estradiol (β = decrease, p = 6.54 × 10⁻³¹) and FSH (β = increase, p = 1.59 × 10⁻¹⁶), achieving genome-wide significance at both phenotypes — a rare finding for a single intronic variant simultaneously influencing an upstream regulator (FSH) and its downstream hormone (estradiol).

A replication study of 1,687 Japanese men⁵⁵ replication study of 1,687 Japanese men
Sato et al. Journal of Human Genetics, 2016 independently confirmed the FSH association (βSTD = 0.15, p = 9.7 × 10⁻⁵) and extended findings to semen quality: the A allele was associated with higher sperm concentration (βSTD = 0.073, p = 0.032) and higher total sperm number (βSTD = 0.074, p = 0.027). The positive direction of semen quality associations — despite the A allele's lower estradiol — is consistent with the mechanism above: reduced estrogen feedback → higher FSH → stronger Sertoli cell stimulation → increased sperm production.

Beyond reproductive endpoints, a life-course BMD meta-analysis across 66,628 individuals in 30 GWAS datasets⁶⁶ life-course BMD meta-analysis across 66,628 individuals in 30 GWAS datasets
Medina-Gomez et al. American Journal of Human Genetics, 2018 identified rs2414095 at the CYP19A1 locus as significantly associated with total body bone mineral density (β = 0.0401 unit decrease, p = 6 × 10⁻¹⁰). Estradiol is the primary sex steroid that protects BMD in both sexes; lower aromatase activity in A allele carriers is a plausible driver of this skeletal effect.

A large multi-ancestry PSA GWAS in 392,522 men⁷⁷ large multi-ancestry PSA GWAS in 392,522 men
Hoffmann et al. Nature Genetics, 2025 also identified rs2414095 as associated with PSA levels (β = 0.0109, p = 7 × 10⁻⁹), suggesting that the androgen–estrogen balance influenced by this variant affects prostate-specific antigen⁸⁸ prostate-specific antigen
PSA is produced by the prostate under androgen stimulation; estrogens modulate androgen receptor sensitivity and are known to suppress PSA expression in prostate epithelium levels.

Practical Actions

For men carrying the A allele, the biological picture is nuanced. Lower estradiol is associated with higher FSH and improved semen parameters in population studies — suggesting the A allele may actually support spermatogenesis. However, estradiol also plays important roles in men: it supports bone density, has favorable cardiovascular effects, and contributes to libido and erectile function. Markedly low estradiol in men (typically below 20 pg/mL) is associated with fat accumulation, bone loss, and sexual dysfunction. The modest allele effect at rs2414095 is unlikely to push estradiol to clinically deficient levels on its own, but it may combine with other factors (obesity, aging, other CYP19A1 variants) to produce a measurable hormonal shift.

For women, the A allele's lower aromatase activity may affect the follicular phase estrogen environment. This is particularly relevant during ART, where aromatase activity influences the estrogenic milieu during ovarian stimulation. Women who also carry other low-activity CYP19A1 variants (such as rs1062033 C allele) may have a compound effect on aromatase output worth discussing with a reproductive endocrinologist.

The BMD association is the most clinically actionable finding for the general population: carriers — especially postmenopausal women and older men — should ensure adequate bone health surveillance and calcium/vitamin D optimization.

Interactions

rs1062033 (CYP19A1 intronic, ~12 kb upstream): This CYP19A1 regulatory variant also reduces aromatase expression, with the C allele associated with lower bone estrogen production and reduced BMD in women. Carriers of the A allele at rs2414095 who also carry the C allele at rs1062033 may have compounded reduction in aromatase activity. The combined effect on estradiol levels and BMD deserves investigation, though a formal compound action should only be proposed after verifying independence of the two signals.

rs700519 (CYP19A1 Arg264Cys): The coding variant Arg264Cys at position 264 of the aromatase protein has in vitro evidence of increased catalytic activity. Individuals carrying the Cys264 variant (rs700519 A allele) alongside the lower-expression rs2414095 A allele present an interesting theoretical antagonism — higher-activity enzyme but potentially lower total expression — though no published study has examined this combination directly.