Genetic Etiology of Permanent Congenital Hypothyroidism in Korean Patients: A Whole-Exome Sequencing Study

Congenital hypothyroidism (CH) is among the most common endocrine disorders in neonates. Genetic testing is essential for elucidating the underlying etiology, especially in cases of permanent CH. We enrolled 32 patients diagnosed with permanent CH from the Pediatric Endocrinology Clinics at Jeju National University Hospital and Soonchunhyang University Cheonan Hospital. Whole-exome sequencing (WES) was performed on genomic DNA extracted from buccal swabs. Variants were classified according to guidelines established by the American College of Medical Genetics and Genomics (ACMG) and the Association for Molecular Pathology (AMP). WES identified 21 distinct genetic variants in 20 of the 32 patients (62.5%), spanning 6 CH-related genes: <i>DUOX2</i>, <i>DUOXA2</i>, <i>TPO</i>, <i>PAX8</i>, <i>TG</i>, and <i>TSHR</i>. Of these, 12 variants classified as pathogenic or likely pathogenic were detected in 15 patients (50%). When classified by inheritance patterns, nine patients had either homozygous (n = 1) or compound heterozygous (n = 8) variants, four patients exhibited oligogenic variants, and two patients carried a single heterozygous variant with pathogenicity. The most frequently affected gene was <i>DUOX2</i>, with pathogenic or likely pathogenic variants found in six patients. Notably, none of the six patients with thyroid agenesis or ectopic thyroid glands harbored detectable pathogenic variants. Our findings underscore the critical role of genetic analysis in determining the etiology of permanent CH. Whole-exome sequencing demonstrated a high prevalence of pathogenic variants, particularly in <i>DUOX2,</i> in Korean patients with CH. These data enhance our understanding of the genetic architecture of CH and have important implications for personalized treatment and genetic counseling.