Familial Dysalbuminemic Hyperthyroxinemia: Cumulative Experience in 29 Consecutive Patients

Abstract

The syndrome of familial dysalbuminemic hyperthyroxinemia (FDH), an inherited abnormality characterized by the presence of a variant serum albumin with preferential affinity for T4, is recognized with increasing frequency as a cause of elevated total and free T4 serum values in clinically euthyroid patients with normal TSH levels. Hyperthyroxinemia caused by this syndrome is occasionally confused with hyperthyroidism or thyroid hormone resistance syndromes, which may prompt unnecessary treatment. To better define the clinical and biochemical characteristics of patients with FDH, we undertook a retrospective analysis of the experience at our institution with this condition. We reviewed our cumulative experience in 29 consecutive patients with FDH diagnosed between 1970 and 1991. FDH was diagnosed in 18 males and 11 females (mean age, 42.7 years) on the basis of clinical euthyroidism, increased total T4 and increased/normal free T4 serum values, normal T3 and TSH serum values, increased T4 binding to serum albumin, and low/normal T4 binding to T4-binding globulin and serum prealbumin. Clinical thyroid examination revealed no abnormalities except for goitre in five patients, and the results of radioiodine uptake studies were normal. Patients with subsequently documented FDH were referred for evaluation of "unusual" findings on thyroid function tests or FDH was detected on routine thyroid function tests or identified on family screening. Euthyroid hyperthyroxinemia in combination with a family history compatible with FDH correctly suggested FDH in seven patients. Clinical euthyroidism in conjunction with a normal basal sensitive TSH value in a hyperthyroxinemic patient differentiates euthyroid hyperthyroxinemia from thyrotoxicosis, obviating unnecessary therapy. Detection of excessive thyroxine binding to serum albumin establishes the diagnosis of FDH and allows it to be differentiated from thyroid hormone resistance syndromes. After a diagnosis of FDH has been established, family screening is advisable. Hyperthyroxinemia in clinically euthyroid patients ("euthyroid hyperthyroxinemia") is recognized with increasing frequency and should prompt a careful diagnostic evaluation. The differential diagnosis of this condition may be difficult because it includes various common and unusual syndromes, including quantitative or qualitative changes in thyroid hormone-binding proteins, circulating antibodies against thyroid hormones, resistance to thyroid hormones, influences from drugs, and acute somatic or psychiatric illness (1). The recently recognized syndrome of familial dysalbuminemic hyperthyroxinemia (FDH), an inherited abnormality with autosomal dominant transmission, is characterized by the presence of a variant serum albumin with preferential affinity for T4 (2-4). Typically, FDH is detected incidentally or patients are referred to endocrinologists on the basis of "unusual" results on routine thyroid function testing, revealing consistently elevated total T4 and elevated or normal free T4 values in a clinically euthyroid patient with normal TSH levels (1,5). Unfortunately, hyperthyroxinemia due to FDH may be confused with hyperthyroidism or thyroid hormone resistance syndromes, prompting repeated unnecessary laboratory testing and possibly even inappropriate treatment (1,3,6,7). Herein, we describe the clinical and biochemical characteristics of 29 consecutive patients with documented FDH.