Familial Dysalbuminaemic Hyperthyroxinaemia (FDH) is a relatively common (1/10000) euthyroid condition where variant albumin has increased affinity for thyroxine (T4). The most common FDH albumin variant is 218Arg>His.
Dystransthyretin Hyperthyroxinaemia (DTTRH) is another euthyroid condition where variant transthyretin (pre-albumin) has increased affinity for T4. Presence of FDH and DTTRH variants can result in abnormal thyroid function tests and diagnosis of variants is required to prevent unnecessary intervention in clinically euthyroid patients.
While the most common FDH albumin variant 218Arg>His has a characteristic mass change (decrease of 19 Da), other albumin variants or transthyretin variants may have less specific mass changes and may require genetic testing of Albumin or TTR genes for confirmation of whether the variant is clinically significant. If this is needed, EDTA whole blood will be required for DNA extraction and testing.
albumin variants, FDH
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