Germline loss-of-function PAM variants are enriched in subjects with pituitary hypersecretion

Abstract

IntroductionPituitary adenomas (PAs) are common, usually benign tumors of the anterior pituitary gland which, for the most part, have no known genetic cause. PAs are associated with major clinical effects due to hormonal dysregulation and tumoral impingement on vital brain structures. PAM encodes a multifunctional protein responsible for the essential C-terminal amidation of secreted peptides.MethodsFollowing the identification of a loss-of-function variant (p.Arg703Gln) in the peptidylglycine a-amidating monooxygenase (PAM) gene in a family with pituitary gigantism, we investigated 299 individuals with sporadic PAs and 17 familial isolated PA kindreds for PAM variants. Genetic screening was performed by germline and tumor sequencing and germline copy number variation (CNV) analysis.ResultsIn germline DNA, we detected seven heterozygous, likely pathogenic missense, truncating, and regulatory SNVs. These SNVs were found in sporadic subjects with growth hormone excess (p.Gly552Arg and p.Phe759Ser), pediatric Cushing disease (c.-133T>C and p.His778fs), or different types of PAs (c.-361G>A, p.Ser539Trp, and p.Asp563Gly). The SNVs were functionally tested in vitro for protein expression and trafficking by Western blotting, splicing by minigene assays, and amidation activity in cell lysates and serum samples. These analyses confirmed a deleterious effect on protein expression and/or function. By interrogating 200,000 exomes from the UK Biobank, we confirmed a significant association of the PAM gene and rare PAM SNVs with diagnoses linked to pituitary gland hyperfunction.ConclusionThe identification of PAM as a candidate gene associated with pituitary hypersecretion opens the possibility of developing novel therapeutics based on altering PAM function.

PAM variants in patients with thyrotrophinomas, cyclical Cushing’s disease and prolactinomas

“…None of the study subjects were part of the original cohort published by Trivellin et al. ( 3 ). Cyclical Cushing’s disease was defined by biochemical documentation of episodic cortisol excess interspersed by periods of normal or low cortisol secretion ( 8 ).…”

“…PAM is a newly implicated gene in pituitary tumorigenesis, with the princeps study by Trivellin et al. earlier this year demonstrating loss-of-function PAM variants across hypersecretory pituitary adenoma subtypes in patients from different centres in United States and Europe ( 3 ). Out of 299 individuals with sporadic pituitary adenomas and 18 kindreds with familial isolated pituitary adenomas, they identified seven PAM variants with deleterious effects on protein expression and/or function.…”

“…Through this and other mechanisms, PAM is essential to the biosynthesis and regulated processing and secretion of multiple pituitary and hypothalamic peptide hormones in addition to many neuropeptides. PAM contains two enzymatic domains – peptidylglycine α-hydroxylating monooxygenase (PHM) and peptidyl-α-hydroxyglycine α-amidating lyase (PAL) – which act sequentially to generate C-terminal amidated peptides ( 3 , 5 ). PAM expression in the pituitary gland is demonstrated in the GTEx ( https://gtexportal.org ) and Human Protein Atlas ( https://www.proteinatlas.org ) databases, and this has been confirmed by dedicated pituitary studies ( 3 , 6 ).…”

“…To date, the Trivellin et al. study is the only evidence of a role for PAM variants in pituitary tumorigenesis ( 3 ). By contrast, PAM variants have an established role in being associated with increased risk of type 2 diabetes mellitus (T2DM) ( 4 ).…”

Tall stature and gigantism in transition age: clinical and genetic aspects—a literature review and recommendations

“…These patients varied from micro- to macroadenomas. Further studies, including more subjects affected by the most common pituitary hypersecretion such as hyperprolactinemia, are needed to better explain the possible role of PAM in pituitary tumorigenesis [ 64 ].…”