The long-range interaction between two GNAS imprinting control regions delineates pseudohypoparathyroidism type 1B pathogenesis

Pseudohypoparathyroidism Type IB with Subclinical Hypothyroidism: a Pedigree Investigation and Literature Review

Pseudohypoparathyroidism (PHP) is a rare genetic disease characterized by hypocalcemia, hyperphosphatemia, and elevated parathyroid hormone (PTH) in serum. Here, we report a case of a patient with pseudohypoparathyroidism type IB (PHPIB) and subclinical hypothyroidism, analyze the clinical and genetic data of his family members, review the relevant literature, and classify and discuss the pathogenesis and clinical characteristics of each subtype. Finally, we discuss the treatment approach to improve clinicians' understanding of the disease.

Human Reproduction and Disturbed Genomic Imprinting

Genomic imprinting is a specific mode of gene regulation which particularly accounts for the factors involved in development. Its disturbance affects the fetus, the course of pregnancy and even the health of the mother. In children, aberrant imprinting signatures are associated with imprinting disorders (ImpDis). These alterations also affect the function of the placenta, which has consequences for the course of the pregnancy. The molecular causes of ImpDis comprise changes at the DNA level and methylation disturbances (imprinting defects/ImpDefs), and there is an increasing number of reports of both pathogenic fetal and maternal DNA variants causing ImpDefs. These ImpDefs can be inherited, but prediction of the pregnancy complications caused is difficult, as they can cause miscarriages, aneuploidies, health issues for the mother and ImpDis in the child. Due to the complexity of imprinting regulation, each pregnancy or patient with suspected altered genomic imprinting requires a specific workup to identify the precise molecular cause and also careful clinical documentation. This review will cover the current knowledge on the molecular causes of aberrant imprinting signatures and illustrate the need to identify this basis as the prerequisite for personalized genetic and reproductive counselling of families.

The role of genetic and epigenetic GNAS alterations in the development of early-onset obesity

BACKGROUND

GNAS (guanine nucleotide-binding protein, alpha stimulating) is an imprinted gene that encodes Gsα, the α subunit of the heterotrimeric stimulatory G protein. This subunit mediates the signalling of a diverse array of G protein-coupled receptors (GPCRs), including the melanocortin 4 receptor (MC4R) that serves a pivotal role in regulating food intake, energy homoeostasis, and body weight. Genetic or epigenetic alterations in GNAS are known to cause pseudohypoparathyroidism in its different subtypes and have been recently associated with isolated, early-onset, severe obesity. Given the diverse biological functions that Gsα serves, multiple molecular mechanisms involving various GPCRs, such as MC4R, β2- and β3-adrenoceptors, and corticotropin-releasing hormone receptor, have been implicated in the pathophysiology of severe, early-onset obesity that results from genetic or epigenetic GNAS changes.

SCOPE OF REVIEW

This review examines the structure and function of GNAS and provides an overview of the disorders that are caused by defects in this gene and may feature early-onset obesity. Moreover, it elucidates the potential molecular mechanisms underlying Gsα deficiency-induced early-onset obesity, highlighting some of their implications for the diagnosis, management, and treatment of this complex condition.

MAJOR CONCLUSIONS

Gsα deficiency is an underappreciated cause of early-onset, severe obesity. Therefore, screening children with unexplained, severe obesity for GNAS defects is recommended, to enhance the molecular diagnosis and management of this condition.

GNAS locus: bone related diseases and mouse models

GNASis a complex locus characterized by multiple transcripts and an imprinting effect. It orchestrates a variety of physiological processes via numerous signaling pathways. Human diseases associated with the GNAS gene encompass fibrous dysplasia (FD), Albright's Hereditary Osteodystrophy (AHO), parathyroid hormone(PTH) resistance, and Progressive Osseous Heteroplasia (POH), among others. To facilitate the study of the GNAS locus and its associated diseases, researchers have developed a range of mouse models. In this review, we will systematically explore the GNAS locus, its related signaling pathways, the bone diseases associated with it, and the mouse models pertinent to these bone diseases.