Thyroid hormone resistance in blood monocyte cells and elevated serum T3 in patients with autosomal dominant osteopetrosis.

Seven patients with autosomal dominant osteopetrosis from three different families were investigated. They all had the roentgenological type I disease, characterized by universal, symmetrical osteosclerosis and enlarged thickness of the calvarium vault. Serum concentrations of thyroid hormones and the specific nuclear binding of triiodothyronine (T3) in mononuclear blood cells were studied. All patients appeared clinically euthyroid. The serum level of T3 was significantly elevated (serum T3 = 1.89 nmol/l) compared with normal age and sex-matched controls (serum T3 = 1.44 nmol/l, p less than 0.05). The specific maximal nuclear binding capacity of T3 was significantly decreased (MBC = 0.51 fmol T3/mg DNA) in these patients compared with controls (MBC = 1.8 fmol/mg DNA, p less than 0.05) whereas no difference in the equilibrium association constant (Ka) was observed. The decreased specific nuclear binding of T3 and the slightly elevated serum level of T3 might indicate a modest peripheral resistance to T3 in patients with autosomal dominant osteopetrosis type I.