Thyroglobulin-Related Thyroid Dyshormonogenesis Presenting as Congenital Hypothyroidism With Mild Hearing Loss: A Case Report

Congenital hypothyroidism (CH) is one of the most common and preventable causes of neurodevelopmental impairment in childhood.Mutations in the thyroglobulin (TG) gene are a recognised cause of thyroid dyshormonogenesis, with a variable clinical presentation.However, associated hearing abnormalities have rarely been described.We report a case of a two-year-old Chinese male child diagnosed with congenital primary hypothyroidism through newborn screening, with a cord blood thyroid-stimulating hormone level of 781 mIU/L and free thyroxine of 5.4 pmol/L.Thyroid imaging revealed a normally located thyroid gland without enlargement.In addition, the patient failed bilateral newborn hearing screening, with subsequent auditory testing demonstrating mild hearing loss.Serum thyroglobulin (Tg) was undetectable (<0.1 μg/L), raising suspicion of an underlying Tg synthesis defect.Whole-exome sequencing identified two heterozygous pathogenic TG variants (c.274+2T>G and c.1333C>T), supporting a diagnosis of TG-related thyroid dyshormonogenesis.Levothyroxine treatment was commenced on Day 2 of life, with subsequent normalisation of thyroid function and age-appropriate growth and development.This case highlights the diagnostic utility of serum Tg measurement in children with congenital hypothyroidism and a eutopic thyroid gland, as well as the role of genetic testing in supporting the diagnosis.The coexistence of hearing impairment in this patient represents a clinical finding with an uncertain relationship to TG-related dyshormonogenesis and warrants further evaluation.