CYP19A1 rs2414095 — An Intronic Aromatase Variant That Modulates Estradiol and FSH
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 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) | 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 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 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 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 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 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.
Alla genotyper
Two copies of the common G allele; standard aromatase expression and estradiol levels
You have two copies of the G allele at rs2414095, the common variant associated with standard aromatase expression. This is the most frequent genotype globally — roughly 42% of people carry it — with G allele frequency ranging from ~65% in Europeans to ~79% in African populations. Large GWAS studies show GG individuals have the highest circulating estradiol and the lowest FSH levels at this locus, representing the baseline aromatase activity phenotype for CYP19A1 rs2414095.
One copy of the A allele; modestly lower estradiol and slightly elevated FSH compared to GG
You carry one copy of the A allele at rs2414095 alongside one G allele. Heterozygotes represent approximately 45% of the global population. The A allele is associated with reduced aromatase expression, leading to modestly lower circulating estradiol and a compensatory rise in FSH. In men, the A allele in Japanese replication studies was associated with higher sperm concentration and total sperm number — a likely consequence of elevated FSH stimulating Sertoli cells. In both sexes, carrying one A allele may modestly influence bone mineral density, as estradiol is the principal protector of skeletal integrity in both men and postmenopausal women.
Two copies of the A allele; lower estradiol, higher FSH, and lower bone mineral density compared to GG
You carry two copies of the A allele at rs2414095. AA homozygotes represent approximately 12% of the global population (ranging from ~5% in Africans to ~12% in Europeans and ~10% in East Asians). This genotype is associated with the lowest estradiol and highest FSH at this locus, based on genome-wide significant findings in Chinese and Japanese male cohorts (Chen et al. 2013, Sato et al. 2016). The lower estradiol associated with two copies of the A allele has several downstream implications: in men, higher FSH drives stronger Sertoli cell stimulation and is associated with higher sperm counts, but persistently lower estradiol may contribute to lower bone mineral density over time. In women, aromatase activity during the follicular phase may be reduced, potentially affecting granulosa cell estrogen output during follicle development. The BMD association (β = 0.0401 per A allele, p = 6 × 10⁻¹⁰ in 66,628 individuals) means AA homozygotes may carry approximately twice the per-allele BMD effect at this locus compared with AG carriers.