RESUMO
OBJECTIVE: Subclinical hypothyroidism (SCH) is defined as high levels of TSH in the presence of normal levels of serum FT4. Since thyroid peroxidase (TPO) plays a key role in thyroid hormone synthesis, variations in the TPO gene can change the enzyme structure and result in the production of anti-TPO antibodies. The aim of this study was to examine the relationship between the Asn698Thr (A2095C) and Thr725Pro (A2173C) polymorphisms of the TPO gene and anti-TPO levels in patients with SCH. DESIGN: In this study, 150 individuals (75 cases and 75 controls), aged 19-75 years, were selected randomly by a clinician. The thyroid function tests included were FT3, FT4, TSH and anti-TPO antibodies using ELISA. The TPO gene polymorphisms were examined by PCR-RFLP. RESULTS: Anti-TPO levels in the experimental group was significantly increased (P=0.020). The A2095C genotype frequency in the experimental and control groups were 37.3% vs 34.7% for the AA healthy genotype, 20% vs 46.7% for AC and 42.7% vs 18.6% for CC, respectively (P=0.001). The A2173C genotype frequency in the experimental and control groups were 22.6% vs 68% for healthy AA, 40% vs 25.3% for AC and 37.4% vs 6.7% for CC, respectively (P <0.001). The increased anti-TPO antibodies were significantly associated with the A2173C polymorphism (P=0.035). The findings showed that the chance (odds ratio) of developing subclinical hypothyroidism in individuals who had C alleles was 1.5 and 5.6-fold higher than in individuals without these alleles in the A2095C and A2173C regions, respectively. CONCLUSIONS: Determination of anti-TPO antibody levels and exon 12 TPO gene polymorphisms in patients with SCH can be helpful for prediction of overt hypothyroidism.