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

Abstract

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/1) compared with normal age and sex-matched controls (serum T₃=1.44 nmol/1, p<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<0.05) whereas no difference in the equilibrium association constant (K_a) 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.

Key Words:

• bone resorption
• osteopetrosis
• thyroid hormones
• triiodothyronine receptors