A Founder Mutation in the POMC 5'-UTR Causes Proopiomelanocortin Deficiency Through Splicing-Mediated Decrease of mRNA

Context: The syndrome of adrenal insufficiency, obesity, and red hair is a rare autosomal recessive disorder. The majority of disease-causing variants associated with the syndrome are located in the coding region of the POMC gene.

Objective: This work describes 7 unrelated patients who shared a novel homozygous mutation in the 5'-untranslated region (UTR) of the POMC gene and functionally characterize this novel variant.

Methods: Whole-exome sequencing (WES) with autozygosity mapping, Sanger sequencing, model expression system studies, and RNA sequencing were used for identification of the disease-causing variant and its subsequent functional characterization. Seven unrelated patients of the Perm Tatar ethnic group presented with hypoglycemia and excessive weight gain, low plasma adrenocorticotropin, and cortisol. Five of 7 children had red hair; 6 of 7 patients also showed signs of bronchial obstruction.

Results: WES showed shared autozygosity regions overlapping the POMC gene. Sanger sequencing of the POMC 5'-UTR detected a homozygous variant chr2:25391366C > T (hg19) at the splice donor site of intron 1. As demonstrated by the model expression system, the variant led to a significant decrease in the POMC messenger RNA level. Analyses of the patients' haplotypes were suggestive of the founder effect. We estimate that the mutation must have occurred at least 4.27 generations ago (95% CI, 0.86-7.67).

Conclusion: This report presents a new molecular mechanism of POMC deficiency and contributes to the information on phenotypic variability in patients with this disorder.