Genetic Screening and Functional Analysis of Thyroid Peroxidase Variants in Chinese Patients with Congenital Hypothyroidism

<b><i>Introduction:</i></b> Congenital hypothyroidism (CH), the most common neonatal endocrine disorder worldwide, can be caused by variants in the thyroid peroxidase (<i>TPO</i>) gene. This study aimed to identify <i>TPO</i> variants in Chinese patients with CH, analyze their impact on TPO function, and establish relationships between <i>TPO</i> genotypes and clinical characteristics. <b><i>Methods:</i></b> A total of 328 patients with CH were screened for <i>TPO</i> variants by performing whole-exome sequencing. The function of the detected <i>TPO</i> variants was investigated via transfection assays in vitro. The pathogenic effect of five novel variants was further assessed in silico. <b><i>Results:</i></b> Among 328 patients with CH, 19 <i>TPO</i> variants, including six novel ones, were identified in 43 patients. Eighteen patients (5.5%) carried biallelic <i>TPO</i> variants. In vitro experiments showed that TPO activity was impaired to varying degrees in 17 variants. Furthermore, we determined that a residual TPO enzyme activity threshold of 15% may serve as a criterion for differentiating CH severity. <b><i>Conclusions:</i></b> According to our study, the prevalence of <i>TPO</i> variants among Chinese patients with CH was 13.1%. Five novel variants led to impaired TPO function by altering its structure or by affecting its expression or cellular localization, which should result in impaired thyroid hormone synthesis.