Mutations in GPR101 as a potential cause of X-linked acrogigantism and acromegaly

Structure of GPR101-Gs enables identification of ligands with rejuvenating potential

GPR101 is an orphan G protein-coupled receptor actively participating in energy homeostasis. Here we report the cryo-electron microscopy structure of GPR101 constitutively coupled to Gs heterotrimer, which reveals unique features of GPR101, including the interaction of extracellular loop 2 within the 7TM bundle, a hydrophobic chain packing-mediated activation mechanism and the structural basis of disease-related mutants. Importantly, a side pocket is identified in GPR101 that facilitates in silico screening to identify four small-molecule agonists, including AA-14. The structure of AA-14-GPR101-Gs provides direct evidence of the AA-14 binding at the side pocket. Functionally, AA-14 partially restores the functions of GH/IGF-1 axis and exhibits several rejuvenating effects in wild-type mice, which are abrogated in Gpr101-deficient mice. In summary, we provide a structural basis for the constitutive activity of GPR101. The structure-facilitated identification of GPR101 agonists and functional analysis suggest that targeting this orphan receptor has rejuvenating potential.

A Chinese Case of X-Linked Acrogigantism and Systematic Review

INTRODUCTION

This study described a Chinese case of X-linked acrogigantism (X-LAG) and summarized the characteristics and treatment of all reported cases.

METHODS

Clinical materials and biological samples from a 5-year and 2-month-old female due to "growth acceleration for 4 years" were collected. Array comparative genomic hybrid (aCGH) and further verification were performed. All X-LAG cases from the PubMed and Web of Science databases were collected and summarized with available data.

RESULTS

The patient presented accelerating growth since 1 year, and her height reached 134.6 cm (+5.24 standard deviation score [SDS]) when she was 5-year and 2-month old. She also had coarsening facial features, snoring, and acral enlargement. Growth hormone (GH) was not suppressed by the glucose-GH inhibition test, and insulin-like growth factor 1 (IGF-1) and prolactin (PRL) levels were elevated. Pituitary MRI revealed a pituitary enlargement with a maximum diameter of 22.3 mm. Octreotide imaging indicated the presence of a pituitary adenoma. The tumor shrank slightly after 3 courses of somatostatin analog but without clinical or biochemical remissions, of which the GH nadir value was 9.4 ng/mL, and IGF-1 was elevated to 749 ng/mL. Therefore, she underwent transsphenoidal surgery. Immunohistochemistry showed GH-positive and PRL-positive cells in the pituitary adenoma. Xq26.3 microduplication of the patient's germline DNA was identified by aCGH. Of all 35 reported cases, females accounted for 71.43%. There were 93.10% and 53.83% patients with hyperprolactinemia and hyperinsulinemia, respectively. Pathology showed that 75.00% of cases were adenomas. Ninety percent of cases had germline variants. The clinical and biochemical remission rates were 78.26% and 82.61%, respectively. However, the rate of complication occurrence during therapy reached 80%.

CONCLUSION

It is important to recognize the possibility of X-LAG when a child under 2-year old presents overgrowth. Early diagnosis and treatment are of great importance for better treatment efficacy and clinical outcome.

Mutations in G Protein-Coupled Receptors: Mechanisms, Pathophysiology and Potential Therapeutic Approaches

There are approximately 800 annotated G protein-coupled receptor (GPCR) genes, making these membrane receptors members of the most abundant gene family in the human genome. Besides being involved in manifold physiologic functions and serving as important pharmacotherapeutic targets, mutations in 55 GPCR genes cause about 66 inherited monogenic diseases in humans. Alterations of nine GPCR genes are causatively involved in inherited digenic diseases. In addition to classic gain- and loss-of-function variants, other aspects, such as biased signaling, trans-signaling, ectopic expression, allele variants of GPCRs, pseudogenes, gene fusion, and gene dosage, contribute to the repertoire of GPCR dysfunctions. However, the spectrum of alterations and GPCR involvement is probably much larger because an additional 91 GPCR genes contain homozygous or hemizygous loss-of-function mutations in human individuals with currently unidentified phenotypes. This review highlights the complexity of genomic alteration of GPCR genes as well as their functional consequences and discusses derived therapeutic approaches. SIGNIFICANCE STATEMENT: With the advent of new transgenic and sequencing technologies, the number of monogenic diseases related to G protein-coupled receptor (GPCR) mutants has significantly increased, and our understanding of the functional impact of certain kinds of mutations has substantially improved. Besides the classical gain- and loss-of-function alterations, additional aspects, such as biased signaling, trans-signaling, ectopic expression, allele variants of GPCRs, uniparental disomy, pseudogenes, gene fusion, and gene dosage, need to be elaborated in light of GPCR dysfunctions and possible therapeutic strategies.

Genetics of Growth Disorders-Which Patients Require Genetic Testing?

The second 360° European Meeting on Growth Hormone Disorders, held in Barcelona, Spain, in June 2017, included a session entitled Pragmatism vs. Curiosity in Genetic Diagnosis of Growth Disorders, which examined current concepts of genetics and growth in the clinical setting, in terms of both growth failure and overgrowth. For patients with short stature, multiple genes have been identified that result in GH deficiency, which may be isolated or associated with additional pituitary hormone deficiencies, or in growth hormone resistance, primary insulin-like growth factor (IGF) acid-labile subunit deficiency, IGF-I deficiency, IGF-II deficiency, IGF-I resistance, and primary PAPP-A2 deficiency. While genetic causes of short stature were previously thought to primarily be associated with the GH-IGF-I axis, it is now established that multiple genetic anomalies not associated with the GH-IGF-I axis can result in short stature. A number of genetic anomalies have also been shown to be associated with overgrowth, some of which involve the GH-IGF-I axis. In patients with overgrowth in combination with an intellectual disability, two predominant gene families, the epigenetic regulator genes, and PI3K/AKT pathway genes, have now been identified. Specific processes should be followed for decisions on which patients require genetic testing and which genes should be examined for anomalies. The decision to carry out genetic testing should be directed by the clinical process, not merely for research purposes. The intention of genetic testing should be to direct the clinical options for management of the growth disorder.