Endocrine Abstracts

Objectives: Male pseudohermaphroditism, or Leydig cell hypoplasia (LCH), is an autosomal recessive disorder in individuals with a 46, XY karyotype, characterized by a predominantly female phenotype despite the presence of testicular structures. It is caused by mutations in the luteinizing hormone/chorionic gonadotropin receptor gene (LHCGR), which impair either LH/CG binding or signal transduction. However, molecular analysis has revealed that the LHCGR is apparently normal in about 50% of patients with the full clinical phenotype of LCH. We therefore searched the LHCGR for novel genomic elements causative for LCH.

Methods and results: In the present study we have identified a novel, primate-specific bona fide exon (exon 6A) within the LHCGR gene. It displays composite characteristics of an internal/terminal exon and possesses stop codons triggering nonsense-mediated mRNA decay (NMD) in LHCGR. Transcripts including exon 6A are physiologically highly expressed in human testes and granulosa cells, and result in an intracellular, truncated LHCGR protein of 209 amino acids. We sequenced exon 6A in 21 patients with unexplained LCH and detected mutations in four patients. Functional studies revealed a dramatic increase in the expression of the mutated internal exon 6A transcripts, indicating aberrant NMD. These altered ratios of LHCGR transcripts result in the generation of predominantly nonfunctional LHCGR isoforms, thereby preventing proper expression and functioning.

Conclusions: The identification and characterization of this novel exon identifies a new regulatory element within the genomic organization of LHCGR, important for receptor regulation at the transcriptional level. Mutations in exon 6A can be causative for disorders of sexual development.

Supported by the German Research Foundation (GR 1547/6-2)