Sporadic primary hyperparathyroidism (PHPT), one of the most common endocrine disorders, is characterized by hypercalcemia and elevated PTH levels. The majority of cases are caused by a benign parathyroid adenoma, but somatic or de novo germ-line mutations that lead to adenoma formation have only been identified in few glands. GCMB is a parathyroid-specific transcription factor, which causes hypoparathyroidism when inactivated on both parental alleles or when a dominant-negative, heterozygous mutation is present. It is overexpressed in some parathyroid adenomas, and we therefore tested the hypothesis that GCMB mutations can be a cause of parathyroid adenomas. Nucleotide sequence analysis was performed on all coding exons and exon-intron borders of GCMB in 30 sporadic parathyroid adenomas and we identified several known polymorphisms that were either heterozygous or homozygous. In addition, one of the 30 investigated glands revealed a novel heterozygous missense mutation, c.1144G>A, which introduced methionine at position 382 for valine (V382M), a conserved amino acid residue. Western blot analysis using mutant GCMB (GCMB-V382M) from lysates of transiently transfected DF-1 fibroblasts, luciferase assays using extracts from these cells, and electrophoretic mobility assays failed to reveal differences between wild-type and mutant GCMB in expression level, transactivational capacity, and DNA-binding ability. Furthermore, pulse-chase experiments demonstrated no difference in half-life of wild-type and mutant protein. We conclude that mutations in the transcription factor GCMB do not seem to play a major role in the pathogenesis of PHPT.