MON-612 Familial Dysalbuminemic Hyperthyroxinemia Cases in Five Unrelated Japanese Families and the Influences on Free T4 Measurement

Familial dysalbuminemic hyperthyroxinemia (FDH) is caused by abnormal human serum albumin (HSA) with an increased thyroxine (T4) affinity leading to euthyroid hyperthyroxinemia. In Japanese FDH patients with the HSAR218P mutation, not only one-step but also two-step immunoassays for free T4 (FT4) can yield false-positive results. Therefore, it is difficult to distinguish FDH from syndrome of inappropriate secretion of TSH, even when multiple assays are used. Patient 1 was a 29-year-old pregnant woman. A radiographic examination and hormone stimulation test were not performed. We suspected that the patient had FDH because of her family history such as abnormal thyroid function and hyperthyroxinemia (Total T4 level was greater than the measurement sensitivity). Genetic analysis using direct sequencing for HSA revealed that she was consistent with FDH. She experienced a normal delivery. Other patients were performed the thyroid test with Chief complaints of infertility or depression and their thyroid function abnormalities were pointed out. Thyroid function tests revealed elevated FT4 and FT3 levels; their TSH level was within the reference range in all patients. To investigate T4 to HSA binding, gel filtration high-performance liquid chromatography was used for the biochemical analyses. Furthermore, FT4 was measured in FDH patients using one-step method LUMIPULSE (Fujirebio) using T3 as an antigen and an anti-T4 antibody as a label. The genomic analysis revealed a heterozygous missense mutation in HSA(R218P). In FDH patient sera, the albumin effluent corresponded to the peaks for total T4 (TT4); approximately 60% of the T4 in the effluent was detected as FT4. Mean FT4 level measured with LUMIPULSE was 1.28 ng/dL within the reference value range. In the FDH patients, a relatively larger quantity of T4 was bound to abnormal HSA. This bound T4 was measured as FT4 during the analysis. When thyroid function abnormality without clinical findings is observed, it is considered preferable to understand the antigen and antibody to be used and to select measurement method.