Primary hyperoxaluria type 1: pathophysiology and genetics

Urinary Oxalate Excretion During Pregnancy in Primary Hyperoxaluria Type 1: A Report of 4 Cases

Primary hyperoxaluria (PH) is a rare genetic disorder characterized by excessive oxalate production because of specific gene defects. PH1 is the most prevalent type, causing recurrent kidney stone disease and often leading to chronic kidney disease and kidney failure. Our previous study suggested that pregnancy did not adversely affect kidney function in female patients with PH. In this study, we identified 4 PH1 cases with urinary oxalate (UOx) measurements during pregnancy from the Rare Kidney Stone Consortium and Oxalosis and Hyperoxaluria Foundation PH registry to investigate UOx levels during pregnancy in patients with PH1. The PH Registry is approved by the Institutional Review Board of Mayo Clinic (Rochester, MN). All 4 showed a decrease in UOx during pregnancy when compared with before pregnancy and after delivery. These findings contrast with those of the general population, in which the UOx tends to increase during pregnancy because of a simultaneous physiological increase in the glomerular filtration rate. Elucidating the mechanism underlying reduced UOx during pregnancy in PH1 could suggest novel PH therapies. These findings could also affect the clinical management and have implications regarding the safety of withholding novel PH1-directed molecular therapies that currently have uncertain safety profiles during pregnancy. We highlight the need for additional data on urinary changes in patients with PH and other populations while pregnant to clarify changes in UOx throughout pregnancy.

Nedosiran Safety and Efficacy in PH1: Interim Analysis of PHYOX3

Introduction

Primary hyperoxaluria (PH) is a rare genetic disorder of hepatic glyoxylate metabolism. Nedosiran is an RNA interference (RNAi) therapeutic that the US Food and Drug Administration has approved for treatment of PH1. PHYOX3 is a trial evaluating monthly nedosiran in patients with PH.

Methods

In this PHYOX3 interim analysis, participants with PH1 who continued from a single-dose nedosiran trial (PHYOX1), with no previous kidney or liver transplantation, dialysis, or evidence of systemic oxalosis were eligible. The safety and efficacy of once-monthly nedosiran was assessed over 30 months.

Results

Thirteen participants completed PHYOX1 and continued into PHYOX3. At baseline, the mean (SD) and median (range) age was 24.2 (6.6) years and 23.0 (14-39) years, respectively; 53.8% were female and 61.5% were White. Mean estimated glomerular filtration rate (eGFR) remained stable (62-84.2 mL/min per 1.73 m2) to month 30. Mean 24-hour urinary oxalate (Uox) excretion showed a sustained reduction from baseline of ≥60% at every visit (months 2-30). From month 2, at least 10 of 13 (76.9%) participants achieved normal (<0.46 mmol/24h; upper limit of assay-normal [ULN]) or near-normal (≥0.46 to <0.60 mmol/24h; ≥ULN to <1.3 × ULN) 24-hour Uox excretion. All participants experienced ≥1 adverse event (AE), mostly mild or moderate in severity (primarily, injection site events). Three serious, not treatment-related AEs were reported; there were no deaths or study discontinuations due to AEs.

Conclusion

Nedosiran was well-tolerated in patients with PH1, and treatment resulted in a sustained, substantial reduction in Uox excretion for at least 30 months in this long-term study. No safety signals have been identified to date. The PHYOX3 study is ongoing.

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.

Primary hyperoxaluria: Description of a new oral finding and review of literature

OBJECTIVES

Oro-dental manifestations of hyperoxaluria and dental management of affected patients are rarely reported in the literature. We describe a new oral presentation of primary hyperoxaluria (PH) and review relevant literature about oro-dental manifestations and management of dental complications of hyperoxaluria.

METHODS

A case report of a 44-year-old female who presented with symptoms of temporomandibular joint dysfunction due to hyperoxaluria was described according to the CARE guidelines. In addition, an extensive search of biomedical databases (PubMed, Medline, Google Scholar, and Embase) for articles describing oro-dental manifestations and/or dental management in patients with hyperoxaluria was performed using the key words ("oral" and/or "hyperoxaluria" and/or "dental" and/or "oxalosis"). Included articles were reviewed and data about patient demographics, disease type and stage, oral and dental manifestations, and dental treatment outcome were retrieved and analyzed.

RESULTS

A total of 14 articles describing the oral and dental manifestations in 15 patients with hyperoxaluria were included. Tooth mobility, root resorption, and radiographic alterations were consistently described in all cases. Oral manifestations were described mainly in PH at late stages, and only after the onset of chronic renal disease. Dental management in all reported cases was palliative and aimed to relive pain and treat periodontal infection. Tooth loss due to extraction or uncontrolled mobility was the ultimate outcome in almost all reported cases.

CONCLUSION

Oral and dental manifestations in hyperoxaluria are rarely reported in the literature. Management of tooth mobility and root resorption in hyperoxaluria is challenging and clinical guidelines and evidence-based recommendations are lacking. Early diagnosis and treatment of hyperoxaluria might be the only effective approach to prevent dental and periodontal complications of the disease.

Case Report: effect of lumasiran treatment in a late preterm baby with antenatal diagnosis of primary hyperoxaluria type 1

Background

Primary hyperoxaluria type 1 (PH1) is a rare disease with autosomal recessive transmission, characterized by increased urinary excretion of oxalate, resulting in chronic kidney disease secondary to recurrent urolithiasis, nephrocalcinosis, and accumulation of oxalate in various organs and tissues (systemic oxalosis). Since 2020, an innovative pharmacological approach, namely, lumasiran, has been added to the therapeutic armamentarium (dialysis and liver-kidney transplantation). The purpose of this paper is to describe the effect of lumasiran initiated at 10 days of life in a newborn with prenatally diagnosed PH1. A female fetus was prenatally diagnosed with hyperoxaluria type 1, based on family history and genetic testing. Her brother had the onset of the disease at 2 months of age and underwent liver and kidney transplantation at 13 months and 8 years of age, respectively. The baby was born late preterm at 36 weeks + 4 days of gestation via spontaneous labor, and lumasiran for compassionate use was started on the tenth day of life. At 20 months of age, the baby showed normal urinary oxalate values and kidney function, while the plasma oxalate level was under the threshold of oversaturation. There were no signs of systemic oxalosis.

Conclusions

Early use of lumasiran in young infants, who do not yet show signs of the disease, represents a therapeutic challenge for the pediatric nephrologist. The ability of the drug to act on the hepatocyte of the newborn and the most appropriate dosage to be used in these very young babies have yet to be clarified.

Abnormal Porphyrin Metabolism in Autism Spectrum Disorder and Therapeutic Implications

Autism spectrum disorder (ASD) is a mosaic of neurodevelopmental conditions composed of early-onset social interaction and communication deficits, along with repetitive and/or restricted patterns of activities, behavior, and interests. ASD affects around 1% of children worldwide, with a male predominance. Energy, porphyrin, and neurotransmitter homeostasis are the key metabolic pathways affected by heavy metal exposure, potentially implicated in the pathogenesis of ASD. Exposure to heavy metals can lead to an altered porphyrin metabolism due to enzyme inhibition by heavy metals. Heavy metal exposure, inborn genetic susceptibility, and abnormal thiol and selenol metabolism may play a significant role in the urinary porphyrin profile anomalies observed in ASD. Altered porphyrin metabolism in ASD may also be associated with, vitamin B6 deficiency, hyperoxalemia, hyperhomocysteinemia, and hypomagnesemia. The present review considers the abnormal porphyrin metabolism in ASD in relation to the potential pathogenic mechanism and discusses the possible metabolic therapies such as vitamins, minerals, cofactors, and antioxidants that need to be explored in future research. Such targeted therapeutic therapies would bring about favorable outcomes such as improvements in core and co-occurring symptoms.

Determinants of Kidney Failure in Primary Hyperoxaluria Type 1: Findings of the European Hyperoxaluria Consortium

Introduction

Primary hyperoxaluria type 1 (PH1) has a highly heterogeneous disease course. Apart from the c.508G>A (p.Gly170Arg) AGXT variant, which imparts a relatively favorable outcome, little is known about determinants of kidney failure. Identifying these is crucial for disease management, especially in this era of new therapies.

Methods

In this retrospective study of 932 patients with PH1 included in the OxalEurope registry, we analyzed genotype-phenotype correlations as well as the impact of nephrocalcinosis, urolithiasis, and urinary oxalate and glycolate excretion on the development of kidney failure, using survival and mixed model analyses.

Results

The risk of developing kidney failure was the highest for 175 vitamin-B6 unresponsive ("null") homozygotes and lowest for 155 patients with c.508G>A and c.454T>A (p.Phe152Ile) variants, with a median age of onset of kidney failure of 7.8 and 31.8 years, respectively. Fifty patients with c.731T>C (p.Ile244Thr) homozygote variants had better kidney survival than null homozygotes (P = 0.003). Poor outcomes were found in patients with other potentially vitamin B6-responsive variants. Nephrocalcinosis increased the risk of kidney failure significantly (hazard ratio [HR] 3.17 [2.03-4.94], P < 0.001). Urinary oxalate and glycolate measurements were available in 620 and 579 twenty-four-hour urine collections from 117 and 87 patients, respectively. Urinary oxalate excretion, unlike glycolate, was higher in patients who subsequently developed kidney failure (P = 0.034). However, the 41% intraindividual variation of urinary oxalate resulted in wide confidence intervals.

Conclusion

In conclusion, homozygosity for AGXT null variants and nephrocalcinosis were the strongest determinants for kidney failure in PH1.

Estrogen's Tissue-Specific Regulation of the SLC26A6 Anion Transporter Reveal a Phenotype of Kidney Stone Disease in Estrogen-Deficient Females: A Systematic Review

Kidney stone formation is an intricate process that involves a disruption in the interplay of the multiple organs and systems involved in regulating the concentration of specific ions in the body. Women who have gone through menopause are susceptible to kidney stone disease. This systematic review aims to investigate the potential influence of estrogen on kidney function and oxalate homeostasis, notably through the anion transporter SLC26A6 (also known as putative anion transporter 1 or PAT1) in females. In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 checklist, a systematic search of online databases included Pubmed, ScienceDirect Journals, and Ingenta Connect Journals. Predetermined criteria to include and exclude papers, gathering articles published between 2012 and 2022, were determined. After a thorough analysis, eight articles (three cohorts, one case-control, one in vivo, one in vitro, and two cross-sectional studies) were identified for the final quality assessment review.  The eight selected and quality-assessed articles provided evidence of a directly proportional connection between estrogen and kidney function. A correlation between serum estrogen levels and the development of kidney stone disease was confirmed. Administration of β-estradiol was shown to effectively inhibit the function of the anion transporter PAT1 in a tissue-specific manner. In the case of the kidney, estrogen was observed to down-regulate PAT1, which led to a reduction in oxalate transporting activity and, consequently, a decrease in kidney stone formation. Consensus suggests that serum estrogen levels and optimal kidney functioning are interrelated. Furthermore, analysis of the quality-assessed articles and a comprehensive literature review revealed estrogen's tissue-specific regulation of the PAT1 anion transporter aids in maintaining kidney function and anion homeostasis. Additional research is needed to solidify estrogen's role in kidney stone disease to determine its therapeutic value in clinical practice.

Unusual cause of cerebral calcifications in an 8-year-old girl

Key Clinical Message

Genetic counseling and genetic screening for hyperoxaluria should be recommended for children with urinary lithiasis for early management to avoid progression to oxalosis especially if there is a family history of lithiasis.

Primary hyperoxaluria type 1 (PH1) is caused by a deficiency of the liver peroxisomal enzyme alanine-glyoxylate aminotransferase (AGT) resulting in overproduction of calcium oxalates. In its later stage, a systemic deposit of calcium oxalates is observed. We present the case of an 8-year-old girl with exceptional neurological involvement secondary to this disease.