Resistance to thyrotropin

Area of Science:

• Endocrinology
• Genetics

Background:

• Resistance to thyrotropin (RTSH) is characterized by reduced thyroid follicle cell sensitivity to TSH stimulation due to genetic defects.
• Affected individuals present with elevated serum TSH without goiter, ranging from isolated hyperthyrotropinemia to congenital hypothyroidism with thyroid hypoplasia.
• RTSH defects impact thyroid hormone synthesis and gland growth, involving genes like the TSH receptor and PAX8.

Purpose of the Study:

• To provide a concise overview of defined causes of nonsyndromic RTSH.
• To discuss differential diagnoses for RTSH, including autoimmune conditions, partial iodine organification defects, and syndromic forms.
• To outline implications for the clinical approach to patients with RTSH.

Main Methods:

• Literature review of genetic defects causing resistance to thyrotropin.
• Analysis of TSH receptor and PAX8 gene mutations.
• Genetic mapping of a common third cause of RTSH to chromosome 15.

Main Results:

• Identified inactivating mutations in TSH receptor and PAX8 genes as causes of RTSH.
• Highlighted a third, yet unelucidated, genetic cause mapped to chromosome 15.
• Differentiated nonsyndromic RTSH from autoimmune, partial iodine organification defects, and syndromic forms.

Conclusions:

• Nonsyndromic RTSH results from specific genetic defects affecting TSH action.
• Accurate diagnosis requires differentiating RTSH from other thyroid conditions.
• Understanding RTSH pathophysiology is crucial for effective clinical management.