Background: A mutation in EIF2S3 (NM_001415; Xp22.11) was previously associated with microcephaly and developmental delay in a single pedigree. EIF2S3 encodes the eukaryotic translation initiation factor 2 subunit 3 (eIF2γ), the largest of three EIF2 subunits. EIF2 initiates protein synthesis by forming a ternary complex with GTP and initiator methionyl-tRNA which then binds to the 40S ribosomal subunit, enabling scanning of mRNA from the 5′ end to identify the AUG start codon. Mutations in EIF2S3 have not previously 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 later manifested glucose dysregulation [2 hr blood glucose (BG) 8.4 mmol/L, insulin 22 mU/L on OGTT; late hypoglycaemia with BG 2.7 mmol/L, insulin 5.5 mU/L 5hrs 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 (mothers heterozygous; absent in the ExAc control database). EIF2S3 was strongly expressed in the human embryonic ventral diencephalon, Rathkes pouch, the anterior/posterior pituitary, and pancreatic islets of Langerhan. We have generated a human EIF2S3-knockout pancreatic (1.1B4) cell line, using lentiviral shRNA cassettes. Preliminary data show higher caspase activity with increased apoptosis in EIF2S3-knockout cells.
Conclusion: We report a novel EIF2S3 mutation associated with X-linked hypopituitarism and glucose dysregulation. Preliminary data suggest critical roles for EIF2S3 in both human pituitary development and insulin secretion.
10 - 12 Sep 2016
European Society for Paediatric Endocrinology