Background: EIF2S3 (NM_001415; Xp22.11) mutations have previously been reported in a single pedigree with microcephaly and developmental delay. The gene encodes the eukaryotic translation initiation factor 2 subunit 3 (eIF2γ), the largest of three EIF2 subunits. EIF2 is a heterotrimeric GTP-binding protein, which initiates protein synthesis. It forms a ternary complex, mediating recruitment of initiator methionyl-tRNA to the 40S ribosomal subunit to scan the mRNA from the 5 end, to identify the AUG start codon for protein synthesis. To date, mutations in this gene have not been associated with hypopituitarism.
Objective and hypotheses: To identify the molecular basis for X-linked hypopituitarism by performing X chromosome exome sequencing, expression studies and functional analysis of novel variants.
Patients: Three males (twin brothers and their maternal cousin) presented with hyperinsulinaemic hypoglycaemia, GH and TSH deficiencies, and anterior pituitary hypoplasia. All three males were treated with rhGH, thyroxine and diazoxide. The latter was stopped in the twins at 7 years, one of whom manifested glucose dysregulation (2 hr glucose 8.4 mmol/l, insulin 22 mU/l in OGTT; late hypoglycaemia with BG 2.7 mmol/l and insulin 5.5 mU/l 5 hrs post-glucose load). His brother demonstrated late hypoglycaemia (BG 2.7 mmol/L, insulin 4.8 mU/l). The mothers (sisters) had resolved secondary amenorrhoea. Candidate gene screening for hypopituitarism and hyperinsulinism was negative.
Methods and Results: We identified a novel hemizygous EIF2S3 variant (c.1294C>T, p.P432S) in the three males and their heterozygous mothers. The variant was not present on control databases, including the ExAc Browser (>90,000 alleles). EIF2S3 human embryonic expression analysis revealed strong expression in the ventral diencephalon, Rathkes pouch, the anterior and posterior pituitary, the retina, nasal epithelium and pancreatic islets of Langerhan at CS16, 19, 20, 23 and 8 weeks post-conception. We have generated a human EIF2S3-knockout pancreatic (1.1B4) cell line, using lentiviral shRNA cassettes. Data show a higher caspase activity with increased cell death in EIF2S3-knockout cells.
Conclusion: We report a novel EIF2S3 mutation associated with X-linked hypopituitarism and glucose dysregulation. Data suggest a critical role for EIF2S3 in both human pituitary development and insulin secretion. This is the first reported association of EIF2S3 mutations with pancreatic and hypothalamo-pituitary dysfunction.
23 - 25 Nov 2016
British Society for Paediatric Endocrinology and Diabetes