Autosomal-dominant non-autoimmune hyperthyroidism presenting with neuromuscular symptoms

Neuromuscular presentations are common in thyroid disease, although the mechanism is unclear. In the present study, we investigated the pathogenesis in a boy with autosomal-dominant hyperthyroidism presenting with neuromuscular symptoms.

The TSHr gene was investigated by direct sequencing. Functional properties of the mutant TSHr were investigated during transient expression in COS-7 cells. Family members were investigated by clinical and biochemical examinations.

Sequence analysis revealed a previously reported heterozygous missense mutation Glycine 431 for Serine in the first transmembrane segment, leading to an increased specific constitutive activity. Three additional affected family members carried the same mutation. There was no indication of autoimmune disorder. All symptoms disappeared upon treatment with thacapzol and L-thyroxine and subsequent subtotal thyroidectomy.

The data imply that neuromuscular symptoms can be caused by excessive thyroid hormone levels rather than by autoimmunity.