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Exon Splice Enhancer Mutation (GH-E32A) Causes Autosomal Dominant Growth Hormone Deficiency

Department of Pediatric Endocrinology, Diabetology, and Metabolism (V.P., D.L., A.E., C.E.F., P.E.M.), Inselspital, University Children’s Hospital, CH-3010 Bern, Switzerland; National Institute for Medical Research (J.T., I.C.R.), Mill Hill, London NW7 1AA, United Kingdom; Department of Pediatric Endocrinology, Royal Manchester Children’s Hospital (P.E.C.), Manchester M27 4HA, United Kingdom; Department of Endocrinology (P.J.T.), Christie Hospital, Manchester M20 4BX, United Kingdom; and Biochemistry, Endocrinology, and Metabolism Unit and Developmental Endocrinology Research Group (M.T.D.), Clinical and Molecular Genetics Unit, Institute of Child Health, London WC1N 1EH, United Kingdom

Address all correspondence and requests for reprints to: Professor Dr. Primus E. Mullis, University Children’s Hospital, Pediatric Endocrinology, Inselspital CH-3010 Bern, Switzerland. E-mail: primus.mullis{at}insel.ch.

Context and Objective: Alteration of exon splice enhancers (ESE) may cause autosomal dominant GH 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, and Patients: Confirming the laboratory-derived data, a heterozygous splice enhancer mutation in exon 3 (exon 3 + 2 AC) coding for GH-E32A mutation of the GH-1 gene was found in two independent pedigrees, causing familial IGHD II. Because 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 with the wt-GH. AtT-20 cells coexpressing both wt-GH and GH-E32A presented a significant reduction in cell proliferation as well as GH production after forskolin stimulation when compared with the cells expressing wt-GH. These results were complemented with confocal microscopy analysis, which revealed a significant reduction of the GH-E32A-derived isoform colocalized with secretory granules, compared with 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.