A rare POU1F1 splicing variant causes pituitary hormone deficiency

MARTINEZ MAYER J; SMITH C; VISHNOPOLSKA SA; KITZMAN JO; CAMPER SA; PÉREZ MILLÁN, MARIA I.

Congreso; SAIC; 2020

POU1F1 is a signature pituitary transcription factor that directly regulates the transcription of growth hormone (Gh), prolactin (Prl), and both the alpha (Cga) and beta subunits of thyroid stimulating hormone (Tshb). Multiple missense mutations in POU1F1 have been reported to cause combined pituitary hormone deficiency and/or isolated growth hormone deficiency (IGHD). Alternative splicing in this gene results in two isoforms: the predominant transcriptional activator alpha and the minor isoform beta that acts as a transcriptional repressor. The POU1F1 beta isoform transcript is created by utilization of an upstream splice acceptor sequence in exon 2 which results in a protein with insertion of 26 amino acids that encode an ETS1 binding domain inserted in the transactivation domain. All the reported mutations are in domains shared by the alpha and beta isoforms of POU1F1 and were functionally tested using the alpha isoform only. We performed whole exome sequencing (WES) in a familial case with IGHD and found a heterozygous and synonymous variant (c.150T>G, p.Ser50Ser50) in POU1F1 presented on the affected father and the son. Interestedly, this variant affects POU1F1 splicing without changing the amino acid sequence. By a high throughput reporter assay we found that this variant shift splicing to favor the POU1F1 beta isoform almost exclusively, while retaining its transcriptional repressor activity on the POU1F1 enhancer. Therefore, we conclude that this mutation is causative of the patient?s phenotype, highlighting the importance of a detailed analysis of sequencing results, particularly of synonymous mutations near splicing sites, which are often overlooked.