Impact of CYP2A6 genetic polymorphism on letrozole efficacy in Iraqi women with polycystic ovary syndrome

Abstract

Objectives: This study investigated the effects of a genetic polymorphism in CYP2A6 (CYP2A6∗2, 1799T>A) on the therapeutic response to letrozole in Iraqi women with polycystic ovarian syndrome (PCOS)-induced infertility.

Methods: A prospective, single-center, randomized, controlled pragmatic clinical trial was conducted in 94 Iraqi women with PCOS-induced infertility. The ovulation response to letrozole (2.5 mg/day for 5 days) was assessed via ultrasound (follicle size ≥18 mm) and hormonal assays (follicle-stimulating hormone, luteinizing hormone, estradiol, prolactin, testosterone, and anti-Müllerian hormone). Genotyping of CYP2A6∗2 (1799T>A, rs1801272) was performed using allele-specific PCR on blood-derived DNA, and the distribution of wild-type (AA), heterozygous (AT), and mutant (TT) alleles was recorded. The association between genotype and letrozole efficacy, including follicle size, endometrial thickness, sex hormone levels, and pregnancy incidence, was also evaluated.

Results: The wild-type allele (AA) of the CYP2A6∗2 gene (1799A>T, rs1801272) was widely distributed in approximately 51 (54.26 %) women with PCOS. Heterozygous alleles (AT) and mutant alleles (TT) were present in 2 (2.13 %) and 41 (43.61 %) women with PCOS, respectively. There was no notable difference between infertile women who did or did not respond to letrozole and those who carried different genotypes (wild-type AA, heterozygous AT, and mutant TT) of CYP2A6 (1799T>A) regarding sex hormones, follicle size, endometrial thickness, or incidence of gestation (P > 0.05).

Conclusion: The CYP2A62 (1799T>A) genetic variant was not associated with letrozole efficacy or resistance in Iraqi women with PCOS, suggesting that this polymorphism does not significantly influence therapeutic outcomes.

Keywords: CYP2A6; Genetic variant; Infertility; Letrozole; Response.

Figure 1

Ultrasonographic changes in endometrial thickness and follicle size before and after letrozole administration in women with PCOS with infertility. The figure illustrates the mean (± standard deviation) for endometrial thickness (mm) and follicle size (mm) in women with PCOS with infertility before and after letrozole treatment. Asterisks (∗) denote statistically significant differences (∗P < 0.05) between pre-treatment (red bars) and post-treatment (green bars) measurements, as determined by the Wilcoxon signed-rank test. Error bars represent the standard deviation. The data demonstrate that letrozole significantly increased both endometrial thickness and follicle size, supporting its role in improving ovarian and endometrial responses in PCOS-related infertility.

Figure 2

Agarose gel electrophoresis of CYP2A6∗2 (1799T>A, rs1801272) genotyping in women with PCOS with infertility. The gel image shows PCR products for the CYP2A62∗ variant (1799T>A, rs1801272) with a 342-bp band. Lanes 1–6: Representative samples of wild-type (AA), heterozygous (AT), and mutant (TT) genotypes. Lane M: 100-bp DNA ladder marker. Genotypes were determined by allele-specific PCR, with the wild-type allele (A) and mutant allele (T) distinguished by primer design (Table 1). The clear banding pattern confirms successful amplification and genotyping. Ethidium bromide staining was visualized under UV transillumination. Primer sequences and PCR conditions are provided in Table 1.

Figure 3

Prevalence of CYP2A6∗2 (1799T > A, rs1801272) genotypes in Iraqi women with PCOS-induced infertility. The pie chart illustrates the distribution of CYP2A62∗ (1799T > A) genotypes among 94 Iraqi women with PCOS: wild-type (AA) (54.26 %, n = 51, blue), heterozygous (AT) (2.13 %, n = 2, yellow), and mutant (TT) (43.61 %, n = 41, red). Genotyping was performed via allele-specific PCR (Figure 2).

Figure 4

Baseline plasma concentrations of reproductive hormones stratified by CYP2A6∗2 (1799T>A) genotypes in Iraqi women with PCOS-induced infertility. Box-and-whisker plots compare pre-treatment (cycle day 2) plasma levels of: (A) Follicle-stimulating hormone (FSH; mIU/mL), (B) Luteinizing hormone (LH; mIU/mL), (C) Estradiol (E2; pg/mL), (D) Prolactin (PRL; ng/mL), (E) Testosterone (T; ng/mL), (F) Anti-Müllerian hormone (AMH; ng/mL). Genotype groups: Wild-type (AA; blue), Heterozygous (AT; orange), Mutant (TT; green). Central lines represent medians, boxes show interquartile ranges (IQRs), whiskers extend to 1.5 × IQR. No significant differences were observed between genotypes (Kruskal–Wallis test, P > 0.05) except for FSH and AMH in non-responders (see Table 6). Hormone assays were performed using immuno-enzymatic methods (Methods section).

Figure 5

Ovarian response parameters and pregnancy outcomes across CYP2A6∗2 (1799T>A) genotypes in women with PCOS treated with letrozole. Box-and-whisker plots (A–B) and bar chart (C) display: A. Follicle size (mm), B. Endometrial thickness (mm), Pregnancy incidence (%). Stratified by CYP2A6∗2 genotypes: wild-type (AA; blue), heterozygous (AT; orange), and mutant (TT; green). Central lines represent medians, boxes show interquartile ranges (IQRs), and whiskers extend to minimum and maximum values. Panel C shows absolute counts with percentages. No significant differences were observed between genotypes for any parameter (Kruskal–Wallis test for A-B, chi-square test for C; all P > 0.05). Ultrasound measurements were taken on cycle day 12 post-letrozole administration. Pregnancy was confirmed by β-hCG testing and ultrasound.