Patients with vitiligo vulgaris and healthy controls without a family history of vitiligo were recruited at the Dermatology Department of Hospital Universitario “Dr. José Eleuterio González” in Monterrey, Mexico from May 2023 through May 2024. A total of 84 vitiligo patients (70 women and 14 men) who met the inclusion criteria: Mexican subjects older than 18 years of both sexes, diagnosed with vitiligo vulgaris; and 90 healthy controls (74 women and 16 men) older than 18 years with a negative history of vitiligo and autoimmune/inflammatory diseases were included in this study. All patients were assessed by a dermatologist. This study was approved by Hospital Universitario “Dr. José Eleuterio González”-UANL Research and Ethics Committee (code DE19-00013). All participants gave their prior written informed consent.

A phenol-chloroform extraction was used to isolate genomic DNA from peripheral venous blood from each individual followed by precipitation in absolute ethanol.9 The DNA pellet was resuspended in Tris–EDTA (pH 7.8) at a final concentration of 0.1–1.0μg/μL and stored at −20°C until used for genetic analysis.

The allele frequency of TYR rs7129973 was characterized by PCR-RFLP using a Labnet Multigene OPTIMAX TC9610 thermal cycler (Labnet International; NJ, United States). Primers for TYR rs7129973 (5′-AACGTTAGCTCCAATGCTAACATAC-3′ and 5′-ACCTTGCTTCATCTTCTCTCTTGTA-3′) were obtained from IDT (Coralville; IA, United States). The endonuclease HpyCH4III (New England Biolabs; MA, United States) was used in the restriction analysis according to previously published protocols.10 All digested products were analyzed by electrophoresis in a 2% agarose gel stained with ethidium bromide and visualized in a UVP model 2 UV High-Performance Transilluminator (Upland; CA, United States).

The sample size was estimated according to vitiligo prevalence in Mexico (4%) and with a 99.5% statistical power (Z=2.33), resulting in a minimum sample of 84 subjects.4 The SPSS v21.0 software for windows (IBM, IL; United States) and the Epi-INFO™ 7 statistical program (CDC, United States) were used in the statistical analysis. A Student's t or Mann–Whitney U test for comparisons between 2 groups were used. ANOVA or Kruskal–Wallis H tests were applied for comparisons across 3 groups according to parametric or nonparametric distribution. Tukey, Bonferroni, Tamhane and Dunnet T3 post hoc tests were used for pair-wise comparisons. A Hardy-Weinberg equilibrium test was obtained for the alleles using a goodness-of-fit test, whereas the genotypic dependence between patients and control subjects was determined with a chi-square test. The following gene models were used to assess the association between gene polymorphism and vitiligo vulgaris: dominant (AA vs GA+GG), recessive (GG vs AA+GA), and allele model (A vs G). Any associations between vitiligo and gene polymorphism were detected using logistic regression analyses. Odd ratios were calculated from 2×2 contingency tables. A P<0.05 was considered significant after the Bonferroni correction.

The age of the participants was of 41.3±9.2 years (median, 42.5; range, 51.0) for vitiligo patients and 38.2±12.0 years (median, 35.5, range, 44.0) for healthy controls (P=0.090). The 84 patients included in this study were diagnosed with vitiligo vulgaris according to the clinical sign of the disease. Activity, age of onset, and family history of vitiligo are shown in Table 1. A total of 43 patients (51.2%) had, at least, 1 relative with vitiligo, and 53 (63.1%) of the patients exhibited the disease at ≤30 years of age (e.g., age of onset).

Four of the patients included had type 2 diabetes mellitus (T2DM, 4.8%) and 24 (28.6%) a personal history of thyroid disorders (Table 2), of which hypothyroidism and subclinical hypothyroidism represented 23.8% and 4.8% respectively.

We investigated whether the TYR rs7129973 variant is associated with vitiligo in a sample of Mexican patients and healthy control subjects. The results of our evaluation showed no deviation based on the Hardy–Weinberg equilibrium for control subjects (P=0.534) and vitiligo patients (P=0.870). Furthermore, the comparison of TYR rs7129973 genotype and/or allele frequency between vitiligo and control subjects revealed that the A allele genotypes had a greater frequency across the cohort; in contrast, a clear association could be seen between G allele genotypes and the presence of vitiligo (P=0.004 (Table 3). Furthermore, it was observed that 53 subjects had an age of onset<30 years of age, and no significant relation was observed between this variable and the genotype (AA: 23.63±13.81/GA: 22.87±13.37; P=0.898/GG: 23.54±10.50; P=0.982/GA+GG: 23.04±12.65; P=0.933). Moreover, when stratifying by age of onset (P=0.646), vitiligo activity (P=0.499), family history of vitiligo (P=0.270), and personal history of thyroid disease (P=0.139), no association was observed in relation to TYR rs7129973 genotype (Table 4).