Increase in thyroxine-binding globulin (TBG) in lysinuric protein intolerance

Area of Science:

• Biochemistry
• Endocrinology
• Genetics

Background:

• Lysinuric protein intolerance (LPI) is a rare genetic disorder affecting amino acid transport.
• Patients with LPI often exhibit unexplained elevations in serum protein-bound iodine (PBI).

Purpose of the Study:

• To investigate the underlying causes of increased PBI in patients with LPI.
• To characterize thyroid hormone levels and binding protein concentrations in LPI.

Main Methods:

• Analysis of serum PBI, thyroid binding globulin (TBG), thyroxine (T4), triiodothyronine (T3), and their binding proteins.
• Assessment of free thyroxine index (FTI) and free triiodothyronine index (FT3I).
• Measurement of serum lactic acid dehydrogenase (LDH) and ferritin levels.

Main Results:

• Elevated serum TBG concentration and binding capacity were observed in LPI patients.
• Serum thyroxine and triiodothyronine levels were increased, while FTI remained normal.
• Free triiodothyronine index was slightly elevated, and thyroid hormone binding pre-albumin (TBPA) binding capacity was decreased.
• Elevated serum LDH and ferritin concentrations were consistent findings in all patients.

Conclusions:

• Increased TBG concentration and binding capacity are primary contributors to elevated PBI in LPI.
• The exact reason for increased TBG in LPI remains unclear but may be linked to the primary defect in diaminoacid transport.
• Thyroid hormone dysregulation in LPI involves complex alterations in binding proteins.