A thyroid adenoma in a pubertal male with thyroxine-binding globulin deficiency.

Complete deficiency of thyroxin-binding globulin (TBG-CD) is not commonly associated with clinical symptoms, and little is known about thyroid tumors associated with TBG-CD. We present a case report of an asymptomatic follicular adenoma that spontaneously shrank in a patient with TBG-CD. A previously healthy 13-yr-old male presented with a diffusely swollen thyroid gland. Thyroid function tests revealed low total thyroxin and TBG concentrations, indicating a TBG deficiency. Ultrasonography revealed a mildly swollen thyroid gland with a nodule (14 × 12 × 19 mm) in the left lobe. Genetic analysis of peripheral blood revealed a previously reported SERPINA7 variant, which resulted in complete loss of TBG function. The nodule was identified as a follicular adenoma using fine-needle aspiration. Subsequently, the adenoma shrank without treatment. This pubertal case suggests that careful observation with ultrasonography is warranted for follicular adenoma in patients with TBG deficiency and that treatment may not be required.

Genotype-Phenotype Correlations in 30 Japanese Patients With Congenital Hypothyroidism Attributable to TG Defects.

CONTEXT: Thyroglobulin (Tg), encoded by TG, is essential for thyroid hormone synthesis. TG defects result in congenital hypothyroidism (CH). Most reported patients were born before the introduction of newborn screening (NBS). OBJECTIVE: We aimed to clarify the phenotypic features of patients with TG defects diagnosed and treated since the neonatal period. METHODS: We screened 1061 patients with CH for 13 CH-related genes and identified 30 patients with TG defects. One patient was diagnosed due to hypothyroidism-related symptoms and the rest were diagnosed via NBS. Patients were divided into 2 groups according to their genotypes, and clinical characteristics were compared. We evaluated the functionality of the 7 missense variants using HEK293 cells. RESULTS: Twenty-seven rare TG variants were detected, including 15 nonsense, 3 frameshift, 2 splice-site, and 7 missense variants. Patients were divided into 2 groups: 13 patients with biallelic truncating variants and 17 patients with monoallelic/biallelic missense variants. Patients with missense variants were more likely to develop thyroid enlargement with thyrotropin stimulation than patients with biallelic truncating variants. Patients with biallelic truncating variants invariably required full hormone replacement, whereas patients with missense variants required variable doses of levothyroxine. Loss of function of the 7 missense variants was confirmed in vitro. CONCLUSION: To our knowledge, this is the largest investigation on the clinical presentation of TG defects diagnosed in the neonatal period. Patients with missense variants showed relatively mild hypothyroidism with compensative goiter. Patients with only truncating variants showed minimal or no compensative goiter and required full hormone replacement.