Concurrent TSHR mutations and DIO2 T92A polymorphism result in abnormal thyroid hormone metabolism

Area of Science:

• Endocrinology
• Molecular Biology
• Genetics

Background:

• Deiodinase 2 (DIO2) is vital for thyroid hormone metabolism.
• Mechanisms regulating DIO2 activity are not fully understood.
• Previous studies linked mutations in selenocysteine insertion sequence binding protein 2 and tRNA[Ser]Sec to reduced DIO2 activity.

Purpose of the Study:

• To investigate the molecular mechanisms underlying abnormal thyroid hormone metabolism.
• To explore the combined effect of TSHR mutations and DIO2 T92A SNP on DIO2 activity.
• To assess the clinical relevance of these genetic factors in hypothyroidism.

Main Methods:

• Analysis of two patients with abnormal thyroid hormone metabolism, TSHR mutations, and DIO2 T92A SNP.
• Primary fibroblast culture from a patient to assess basal and TSH-stimulated DIO2 enzymatic activity.
• Evaluation of DIO2 expression levels.

Main Results:

• Patient fibroblasts showed high basal DIO2 enzymatic activity, potentially due to increased DIO2 expression.
• This elevated activity did not respond to TSH stimulation.
• The combination of TSHR mutations and DIO2 T92A SNP ("double hit") significantly reduced TSH-stimulated DIO2 activity.

Conclusions:

• TSHR mutations and DIO2 T92A SNP may act synergistically to impair TSH-mediated DIO2 regulation.
• This genetic interaction could contribute to hypothyroidism in a specific patient subset.
• Patients with this "double hit" may benefit from T3/T4 combination therapy.