Next-generation sequencing in identification of pathogenic variants in primary hyperoxaluria among 21 Egyptian families: Identification of two novel AGXT gene mutations

Exploring the Role of Glycine Metabolism in Coronary Artery Disease: Insights from Human Genetics and Mouse Models

Background: Circulating glycine levels have been associated with reduced risk of coronary artery disease (CAD) in humans but these associations have not been observed in all studies. We evaluated whether the relationship between glycine levels and atherosclerosis was causal using genetic analyses in humans and feeding studies in mice. Methods: Serum glycine levels were evaluated for association with risk of CAD in the UK Biobank. Genetic determinants of glycine levels were identified through a genome-wide association study (GWAS) and used to evaluate the causal relationship between glycine and risk of CAD by Mendelian randomization (MR). A dietary supplementation study was carried out with atherosclerosis-prone apolipoprotein E deficient (ApoE-/-) mice to determine the effects of increased circulating glycine levels on cardiometabolic traits and aortic lesion formation. Results: Among 105,718 UK Biobank subjects, elevated serum glycine levels were associated with significantly reduced risk of prevalent CAD (Quintile 5 vs. Quintile 1 OR = 0.76, 95% CI 0.67-0.87; p < 0.0001) and incident CAD (Quintile 5 vs. Quintile 1 HR = 0.70, 95% CI 0.65-0.77; p < 0.0001) after adjustment for age, sex, ethnicity, anti-hypertensive and lipid-lowering medications, blood pressure, kidney function, and diabetes. A GWAS meta-analysis with 230,947 subjects identified 61 loci for glycine levels, of which 26 were novel. MR analyses provided modest evidence that genetically elevated glycine levels were causally associated with reduced systolic blood pressure and risk of type 2 diabetes, but did not provide significant evidence for an association with decreased risk of CAD. Glycine supplementation in mice had no effects on cardiometabolic traits or atherosclerotic lesion development. Conclusions: While expanding the genetic architecture of glycine metabolism, MR analyses and in vivo feeding studies did not provide evidence that the clinical association of this amino acid with atherosclerosis represents a causal relationship.

A molecular journey on the pathogenesis of primary hyperoxaluria

PURPOSE OF REVIEW

Primary hyperoxalurias (PHs) are rare disorders caused by the deficit of liver enzymes involved in glyoxylate metabolism. Their main hallmark is the increased excretion of oxalate leading to the deposition of calcium oxalate stones in the urinary tract. This review describes the molecular aspects of PHs and their relevance for the clinical management of patients.

RECENT FINDINGS

Recently, the study of PHs pathogenesis has received great attention. The development of novel in vitro and in vivo models has allowed to elucidate how inherited mutations lead to enzyme deficit, as well as to confirm the pathogenicity of newly-identified mutations. In addition, a better knowledge of the metabolic consequences in disorders of liver glyoxylate detoxification has been crucial to identify the key players in liver oxalate production, thus leading to the identification and validation of new drug targets.

SUMMARY

The research on PHs at basic, translational and clinical level has improved our knowledge on the critical factors that modulate disease severity and the response to the available treatments, leading to the development of new drugs, either in preclinical stage or, very recently, approved for patient treatment.

Expanding the Genetic Spectrum of AGXT Gene Variants in Egyptian Patients with Primary Hyperoxaluria Type I

Introduction: Approximately 80% of primary hyperoxaluria cases are caused by primary hyperoxaluria type 1 (PH1, OMIM# 259900), which is characterized by pathogenic variants in the AGXT gene, resulting in deficiency of the liver-specific enzyme alanine-glyoxylate aminotransferase (AGT). This leads to increased production of oxalate, which cannot be effectively eliminated from the body, resulting in its accumulation primarily in the kidneys and other organs. Subjects and Methods: This study included 17 PH1 Egyptian patients from 12 unrelated families, recruited from the Inherited Kidney Disease Outpatient Clinic and the Dialysis Units, Cairo University Hospitals, during the period from January 2018 to December 2019, aiming to identify the pathogenic variants in the AGXT gene. Results: Six different variants were detected. These included three frameshift and three missense variants, all found in homozygosity within the respective families. The most common variant was c.121G>A;p.(Gly41Arg) detected in four families, followed by c.725dup;p.(Asp243GlyfsTer12) in three families, c.33dup;p.(Lys12Glnfs156) in two families, and c.731T >C;p.(Ile244Thr), c.33delC;p.(Lys12Argfs34), and c.568G>A;p.(Gly190Arg) detected in one family each. Conclusion: Consanguineous Egyptian families with history of renal stones or renal disease suspicious of primary hyperoxaluria should undergo AGXT genetic sequencing, specifically targeting exons 1 and 7, as variants in these two exons account for >75% of disease-causing variants in Egyptian patients with confirmed PH1.

Effect of Genetic and Dietary Perturbation of Glycine Metabolism on Atherosclerosis in Humans and Mice

Objective

Epidemiological and genetic studies have reported inverse associations between circulating glycine levels and risk of coronary artery disease (CAD). However, these findings have not been consistently observed in all studies. We sought to evaluate the causal relationship between circulating glycine levels and atherosclerosis using large-scale genetic analyses in humans and dietary supplementation experiments in mice.

Methods

Serum glycine levels were evaluated for association with prevalent and incident CAD in the UK Biobank. A multi-ancestry genome-wide association study (GWAS) meta-analysis was carried out to identify genetic determinants for circulating glycine levels, which were then used to evaluate the causal relationship between glycine and risk of CAD by Mendelian randomization (MR). A glycine feeding study was carried out with atherosclerosis-prone apolipoprotein E deficient (ApoE-/-) mice to determine the effects of increased circulating glycine levels on amino acid metabolism, metabolic traits, and aortic lesion formation.

Results

Among 105,718 subjects from the UK Biobank, elevated serum glycine levels were associated with significantly reduced risk of prevalent CAD (Quintile 5 vs. Quintile 1 OR=0.76, 95% CI 0.67-0.87; P<0.0001) and incident CAD (Quintile 5 vs. Quintile 1 HR=0.70, 95% CI 0.65-0.77; P<0.0001) in models adjusted for age, sex, ethnicity, anti-hypertensive and lipid-lowering medications, blood pressure, kidney function, and diabetes. A meta-analysis of 13 GWAS datasets (total n=230,947) identified 61 loci for circulating glycine levels, of which 26 were novel. MR analyses provided modest evidence that genetically elevated glycine levels were causally associated with reduced systolic blood pressure and risk of type 2 diabetes, but did provide evidence for an association with risk of CAD. Furthermore, glycine-supplementation in ApoE-/- mice did not alter cardiometabolic traits, inflammatory biomarkers, or development of atherosclerotic lesions.

Conclusions

Circulating glycine levels were inversely associated with risk of prevalent and incident CAD in a large population-based cohort. While substantially expanding the genetic architecture of circulating glycine levels, MR analyses and in vivo feeding studies in humans and mice, respectively, did not provide evidence that the clinical association of this amino acid with CAD represents a causal relationship, despite being associated with two correlated risk factors.

New and old approaches to nutritional management of acute and chronic glomerulonephritis

PURPOSE OF REVIEW

It has been well published that a low protein diet (0.6-0.8 g/kg/day) is optimal for nutritional management of chronic kidney disease and with care be used without inducing protein malnutrition.

RECENT FINDINGS

Though care with this approach must be demonstrated in patients with end-stage renal disease and with prominent protein energy wasting, another category of renal patient exists for whom dietary recommendations need more exploration. The Kidney Disease Improving Global Outcomes consortium, actually identifies renal disease as those patients with reduced filtration and those with excessive proteinuria excretion. Proteinuria, indeed, has proven to be a serious marker predisposing renal patients to atherosclerotic heart disease, venous thromboembolism, cerebrovascular accidents, and overall mortality. We discuss what is known about nutritional strategies to curb proteinuria and control inflammation in the setting of glomerulonephritis.

SUMMARY

While this area of management of a set of conditions maybe nascent, it has the potential to provide incredible breakthroughs in nutritional management of auto immune diseases of the kidney specifically and the body writ large.