Context and Objective: Alteration of exon splice enhancers (ESE) may cause autosomal dominant growth hormone deficiency (IGHD II). Disruption analysis of a (GAA) (n) ESE motif within exon 3 by introducing single base mutations has shown that single nucleotide mutations within ESE1 affect pre-mRNA splicing.

Design, Setting, Patients: Confirming the laboratory derived data a heterozygous splice enhancer mutation in exon 3 (E3+2 AC) coding for GH-E32A mutation of the GH-1 gene was found in two independent pedigrees causing familial IGHD II. As different ESE mutations have a variable impact on splicing of exon 3 of GH and, therefore, on the expression of the 17.5 kDa GH mutant form, the GH-E32A was studied at the cellular level.

Interventions and Results: The splicing of GH-E32A, assessed at the protein level, produced significantly increased amounts of 17.5-kDa GH isoform (55% of total GH protein) when compared to the wt-GH. AtT-20 cells co-expressing both wt-GH and GH-E32A, presented a significant reduction in cell proliferation as well as GH production after forskolin stimulation when compared to the cells expressing wt-GH. These results were complemented with confocal microscopy analysis, which revealed a significant reduction of the GH-E32A-derived isoform co-localized with secretory granules compared to wt-GH.

Conclusion: GH-E32A mutation found within ESE1 weakens recognition of exon 3 directly and, therefore, an increased production of the exon 3 skipped 17.5-kDa GH isoform in relation to the 22-kDa, wt-GH isoform was found. The GH-E32A mutant altered stimulated GH-production, as well as cell proliferation, causing IGHD II.