Disorders of fatty acid oxidation and autosomal recessive polycystic kidney disease-different clinical entities and comparable perinatal renal abnormalities

Clinical utility of chromosomal microarray analysis and whole exome sequencing in foetuses with oligohydramnios

OBJECTIVES

To evaluate the clinical utility of chromosomal microarray analysis (CMA) and whole exome sequencing (WES) in foetuses with oligohydramnios.

METHODS

In this retrospective study, 126 fetuses with oligohydramnios at our centre from 2018 to 2021 were reviewed. The results of CMA and WES were analysed.

RESULTS

One hundred and twenty-four cases underwent CMA and 32 cases underwent WES. The detection rate of pathogenic/likely pathogenic (P/LP) copy number variant (CNV) by CMA was 1.6% (2/124). WES revealed P/LP variants in 21.8% (7/32) of the foetuses. Six (85.7%, 6/7) foetuses showed an autosomal recessive inheritance pattern. Three (42.9%, 3/7) variants were involved in the renin-angiotensin-aldosterone system (RAAS), which are the known genetic causes of autosomal recessive renal tubular dysgenesis (ARRTD).

CONCLUSION

CMA has low diagnostic utility for oligohydramnios, while WES offers obvious advantages in improving the detection rate. WES should be recommended for fetuses with oligohydramnios.

Fibrocystin/Polyductin releases a C-terminal fragment that translocates into mitochondria and suppresses cystogenesis

Fibrocystin/Polyductin (FPC), encoded by PKHD1, is associated with autosomal recessive polycystic kidney disease (ARPKD), yet its precise role in cystogenesis remains unclear. Here we show that FPC undergoes complex proteolytic processing in developing kidneys, generating three soluble C-terminal fragments (ICDs). Notably, ICD15, contains a novel mitochondrial targeting sequence at its N-terminus, facilitating its translocation into mitochondria. This enhances mitochondrial respiration in renal epithelial cells, partially restoring impaired mitochondrial function caused by FPC loss. FPC inactivation leads to abnormal ultrastructural morphology of mitochondria in kidney tubules without cyst formation. Moreover, FPC inactivation significantly exacerbates renal cystogenesis and triggers severe pancreatic cystogenesis in a Pkd1 mouse mutant Pkd1V/V in which cleavage of Pkd1-encoded Polycystin-1 at the GPCR Proteolysis Site is blocked. Deleting ICD15 enhances renal cystogenesis without inducing pancreatic cysts in Pkd1V/V mice. These findings reveal a direct link between FPC and a mitochondrial pathway through ICD15 cleavage, crucial for cystogenesis mechanisms.

Autosomal Recessive Polycystic Kidney Disease: Diagnosis, Prognosis, and Management

Autosomal recessive polycystic kidney disease (ARPKD) is the rare and usually early-onset form of polycystic kidney disease with a typical clinical presentation of enlarged cystic kidneys and liver involvement with congenital hepatic fibrosis or Caroli syndrome. ARPKD remains a clinical challenge in pediatrics, frequently requiring continuous and long-term multidisciplinary treatment. In this review, we aim to give an overview over clinical aspects of ARPKD and recent developments in our understanding of disease progression, risk patterns, and treatment of ARPKD.

Role of abnormal energy metabolism in the progression of chronic kidney disease and drug intervention

Chronic kidney disease (CKD) is a severe clinical syndrome with significant socioeconomic impact worldwide. Orderly energy metabolism is essential for normal kidney function and energy metabolism disorders are increasingly recognized as an important player in CKD. Energy metabolism disorders are characterized by ATP deficits and reactive oxygen species increase. Oxygen and mitochondria are essential for ATP production, hypoxia and mitochondrial dysfunction both affect the energy production process. Renin-angiotensin and adenine signaling pathway also play important regulatory roles in energy metabolism. In addition, disturbance of energy metabolism is a key factor in the development of hereditary nephropathy such as autosomal dominant polycystic kidney disease. Currently, drugs with clinically clear renal function protection, such as Angiotensin II Type 1 receptor blockers and fenofibrate, have been proven to improve energy metabolism disorders. The sodium-glucose co-transporter inhibitors 2 that can mediate glucose metabolism disorders not only delay the progress of diabetic nephropathy, but also have significant protective effects in non-diabetic nephropathy. Hypoxia-inducible factor enhances ATP production to the kidney by improving renal oxygen supply and increasing glycolysis, and the mitochondria targeted peptides (SS-31) plays a protective role by stabilizing the mitochondrial inner membrane. Moreover, several drugs are being studied and are predicted to have potential renal protective properties. We propose that the regulation of energy metabolism represents a promising strategy to delay the progression of CKD.

Dietary Interventions in Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by the progressive growth of renal cysts, leading to the loss of functional nephrons. Recommendations for individuals with ADPKD to maintain a healthy diet and lifestyle are largely similar to those for the general population. However, recent evidence from preclinical models suggests that more tightly specified dietary regimens, including caloric restriction, intermittent fasting, and ketogenic diets, hold promise to slow disease progression, and the results of ongoing human clinical trials are eagerly awaited. These dietary interventions directly influence nutrient signaling and substrate availability in the cystic kidney, while also conferring systemic metabolic benefits. The present review focuses on the importance of local and systemic metabolism in ADPKD and summarizes current evidence for dietary interventions to slow disease progression and improve quality of life.

Loss of Mitochondrial Control Impacts Renal Health

Disruption of mitochondrial biosynthesis or dynamics, or loss of control over mitochondrial regulation leads to a significant alteration in fuel preference and metabolic shifts that potentially affect the health of kidney cells. Mitochondria regulate metabolic networks which affect multiple cellular processes. Indeed, mitochondria have established themselves as therapeutic targets in several diseases. The importance of mitochondria in regulating the pathogenesis of several diseases has been recognized, however, there is limited understanding of mitochondrial biology in the kidney. This review provides an overview of mitochondrial dysfunction in kidney diseases. We describe the importance of mitochondria and mitochondrial sirtuins in the regulation of renal metabolic shifts in diverse cells types, and review this loss of control leads to increased cell-to-cell transdifferentiation processes and myofibroblast-metabolic shifts, which affect the pathophysiology of several kidney diseases. In addition, we examine mitochondrial-targeted therapeutic agents that offer potential leads in combating kidney diseases.

Laboratory analysis of acylcarnitines, 2020 update: a technical standard of the American College of Medical Genetics and Genomics (ACMG)

Acylcarnitine analysis is a useful test for identifying patients with inborn errors of mitochondrial fatty acid β-oxidation and certain organic acidemias. Plasma is routinely used in the diagnostic workup of symptomatic patients. Urine analysis of targeted acylcarnitine species may be helpful in the diagnosis of glutaric acidemia type I and other disorders in which polar acylcarnitine species accumulate. For newborn screening applications, dried blood spot acylcarnitine analysis can be performed as a multiplex assay with other analytes, including amino acids, succinylacetone, guanidinoacetate, creatine, and lysophosphatidylcholines. Tandem mass spectrometric methodology, established more than 30 years ago, remains a valid approach for acylcarnitine analysis. The method involves flow-injection analysis of esterified or underivatized acylcarnitines species and detection using a precursor-ion scan. Alternative methods utilize liquid chromatographic separation of isomeric and isobaric species and/or detection by selected reaction monitoring. These technical standards were developed as a resource for diagnostic laboratory practices in acylcarnitine analysis, interpretation, and reporting.

Prenatal and foetal autopsy findings in glutaric aciduria type II

BACKGROUND

Glutaric aciduria type 2 is a rare, lethal disorder that affects metabolism of fatty acids caused by genetic defects in electron transfer (ETF) or in electron transfer flavoprotein dehydrogenase (ETFDH). We aimed to describe the pathological findings of 15 week old foetus, born from a consanguineous couple with 3 previous perinatal deaths. The last son died at 4 days of life and genetic analyses revealed a novel probably pathogenic variant at ETFDH (c.706dupG + c.706dupG) that codifies for a truncated protein (p.Glu236Glyfs*5 + p.Glu236Glyfs*5).

CASE

During the gestation, due to the medical familial history, prenatal echography and a chorial biopsy for ETFDH-associated glutaric aciduria analysis were carried out. Sanger sequencing confirmed the presence of the homozygous familial variant in the ETFDH gene. The gestation was terminated and the foetal autopsy performed. Autopsy revealed prominent forehead, flat nasal bridge, malformed ears, intrauterine growth retardation, polycystic kidneys and steatosis in the liver, consistent with the diagnosis of glutaric aciduria type II. The comparison of present cases with the previously reported in the literature confirmed the presence of classical criteria, but also revealed the association with urogenital deformities, not previously stated.

CONCLUSIONS

Clinical and foetal findings allowed the characterisation of the novel variant (c.706dupG at ETDFH) as pathogenic. Genotype-phenotype relationship is important when studying rare genetic disorders such as glutaric aciduria type II, as variants are usually family-specific, leading to a difficulty in the characterisation of their pathogenicity.

Metabolic Changes in Polycystic Kidney Disease as a Potential Target for Systemic Treatment

Autosomal recessive and autosomal dominant polycystic kidney disease (ARPKD, ADPKD) are systemic disorders with pronounced hepatorenal phenotypes. While the main underlying genetic causes of both ARPKD and ADPKD have been well-known for years, the exact molecular mechanisms resulting in the observed clinical phenotypes in the different organs, remain incompletely understood. Recent research has identified cellular metabolic changes in PKD. These findings are of major relevance as there may be an immediate translation into clinical trials and potentially clinical practice. Here, we review important results in the field regarding metabolic changes in PKD and their modulation as a potential target of systemic treatment.

Late-onset riboflavin-responsive multiple acyl-CoA dehydrogenase deficiency (MADD): case reports and epidemiology of ETFDH gene mutations

BACKGROUND

Multiple acyl-CoA dehydrogenase deficiency (MADD) is a riboflavin-responsive lipid-storage myopathy caused by mutations in the EFTA, EFTB or ETFDH genes. We report a Chinese family of Southern Min origin with two affected siblings with late-onset riboflavin-responsive MADD due to a homozygous c.250G > A EFTDH mutation and review the genetic epidemiology of the c.250G > A mutation.

CASE PRESENTATION

Both siblings presented with exercise-induced myalgia, progressive proximal muscle weakness and high levels of serum muscle enzymes and were initially diagnosed as polymyositis after a muscle biopsy. A repeat biopsy in one sibling subsequently showed features of lipid storage myopathy and genetic analysis identified a homozygous mutation (c.250G > A) in the ETFDH gene in both siblings and carriage of the same mutation by both parents. Glucocorticoid therapy led to improvement in muscle enzyme levels, but little change in muscle symptoms, and only after treatment with riboflavin was there marked improvement in exercise tolerance and muscle strength. The frequency and geographic distribution of the c.250G > A mutation were determined from a literature search for all previously reported cases of MADD with documented mutations. Our study found the c.250G > A mutation is the most common EFTDH mutation in riboflavin-responsive MADD (RR-MADD) and is most prevalent in China and South-East Asia where its epidemiology correlates with the distribution and migration patterns of the southern Min population in Southern China and neighbouring countries.

CONCLUSIONS

Mutations in ETFDH should be screened for in individuals with lipid-storage myopathy to identify patients who are responsive to riboflavin. The c.250G > A mutation should be suspected particularly in individuals of southern Min Chinese background.

Microarray findings in pregnancies with oligohydramnios - a retrospective cohort study and literature review

Objective To explore the risk for abnormal chromosomal microarray analysis (CMA) findings in pregnancies with oligohydramnios. Methods Data from all CMA analyses performed due to oligohydramnios between 2013 and 2017 were retrospectively obtained from the Israeli Ministry of Health database. The rate of clinically significant (pathogenic and likely pathogenic) findings was compared to a local cohort of pregnancies with normal ultrasound, yielding a 1.4% rate of abnormal CMA results. In addition, a search was conducted through the PubMed database addressing the issue. Results Fifty CMA analyses were performed due to oligohydramnios. The 2% risk for clinically significant CMA finding in pregnancies with oligohydramnios did not differ from the control population of 5541 pregnancies with normal ultrasound - relative risk (RR) 1.4 [95% confidence interval (CI) 0.2-10.2]. Literature search yielded 394 titles, of which four relevant articles were selected, all using fetal karyotyping. Conclusion There is yet insufficient evidence to support invasive prenatal testing in pregnancies with isolated oligohydramnios.

Metabolic reprogramming and the role of mitochondria in polycystic kidney disease

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is a slowly progressive disease characterized by the relentless growth of renal cysts throughout the life of affected individuals. Early evidence suggested that the epithelia lining the cysts share neoplastic features, leading to the definition of PKD as a "neoplasm in disguise". Recent work from our and other laboratories has identified a profound metabolic reprogramming in PKD, similar to the one reported in cancer and consistent with the reported increased proliferation. Multiple lines of evidence suggest that aerobic glycolysis (a Warburg-like effect) is present in the disease, along with other metabolic dysfunctions such as an increase in the pentose phosphate pathway, in glutamine anaplerosis and fatty acid biosynthesis, while fatty acid oxidation and oxidative phosphorylation (OXPHOS) are decreased. In addition to glutamine, other amino acid-related pathways appear altered, including asparagine and arginine. The precise origin of the metabolic alterations is not entirely clear, but two hypotheses can be formulated, not mutually exclusive. First, the polycystins have been recently shown to regulate directly mitochondrial function and structure either by regulating Ca²⁺ uptake in mitochondria at the Mitochondria Associated Membranes (MAMs) of the Endoplasmic Reticulum, or by a direct translocation of a small fragment of the protein into the matrix of mitochondria. One alternative possibility is that metabolic and mitochondrial dysfunctions in ADPKD are secondary to the de-regulation of proliferation, driven by the multiple signaling pathways identified in the disease, which include mTORC1 and AMPK among the most relevant. While the precise mechanisms underlying these novel alterations identified in ADPKD will need further investigation, it is evident that they offer a great opportunity for novel interventions in the disease.

Metabolism and mitochondria in polycystic kidney disease research and therapy

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common, potentially lethal, monogenic diseases and is caused predominantly by mutations in polycystic kidney disease 1 (PKD1) and PKD2, which encode polycystin 1 (PC1) and PC2, respectively. Over the decades-long course of the disease, patients develop large fluid-filled renal cysts that impair kidney function, leading to end-stage renal disease in ~50% of patients. Despite the identification of numerous dysregulated pathways in ADPKD, the molecular mechanisms underlying the renal dysfunction from mutations in PKD genes and the physiological functions of the polycystin proteins are still unclear. Alterations in cell metabolism have emerged in the past decade as a hallmark of ADPKD. ADPKD cells shift their mode of energy production from oxidative phosphorylation to alternative pathways, such as glycolysis. In addition, the polycystins seem to play regulatory roles in modulating mechanisms and machinery related to energy production and utilization, including AMPK, PPARα, PGC1α, calcium signalling at mitochondria-associated membranes, mTORC1, cAMP and CFTR-mediated ion transport as well as the expression of crucial components of the mitochondrial energy production apparatus. In this Review, we explore these metabolic changes and discuss in detail the relationship between energy metabolism and ADPKD pathogenesis and identify potential therapeutic targets.

Imaging of Kidney Cysts and Cystic Kidney Diseases in Children: An International Working Group Consensus Statement

Kidney cysts can manifest as focal disease (simple and complex kidney cysts), affect a whole kidney (eg, multicystic dysplastic kidney or cystic dysplasia), or manifest as bilateral cystic disease (eg, autosomal recessive polycystic kidney disease [ARPKD] or autosomal dominant polycystic kidney disease [ADPKD]). In children, as opposed to adults, a larger proportion of kidney cysts are due to genetic diseases (eg, HNF1B nephropathy, various ciliopathies, and tuberous sclerosis complex), and fewer patients have simple cysts or acquired cystic kidney disease. The purpose of this consensus statement is to provide clinical guidance on standardization of imaging tests to evaluate kidney cysts in children. A committee of international experts in pediatric nephrology, pediatric radiology, pediatric US, and adult nephrology prepared systematic literature reviews and formulated recommendations at a consensus meeting. The final statement was endorsed by the European Society of Pediatric Radiology, the European Federation of Societies for Ultrasound in Medicine and Biology, the European Society of Pediatric Nephrology, and reviewed by the European Reference Network for Rare Kidney Diseases. Main recommendations are as follows: US is the method of choice when assessing pediatric kidney cysts, with selected indications for MRI and contrast-enhanced US. CT should be avoided whenever possible because of ionizing radiation. Renal US yields essential diagnostic information in many cases. In patients with ARPKD or other ciliopathies, abdominal US is needed for diagnosis and screening of portal hypertension. US is usually sufficient for follow-up kidney imaging, but MRI can be valuable for clinical trials in patients with ADPKD or in older children with tuberous sclerosis complex to evaluate both kidney cysts and angiomyolipomas.

Prenatal parental decision-making and postnatal outcome in renal oligohydramnios

BACKGROUND

Previous studies on renal oligohydramnios (ROH) report highly variable outcome and identify early onset of ROH and presence of extrarenal manifestations as predictors of adverse outcome in most cases. Data on termination of pregnancy (TOP) and associated parental decision-making processes are mostly missing, but context-sensitive for the interpretation of these findings. We provide here a comprehensive analysis on the diagnosis, prenatal decision-making and postnatal clinical course in all pregnancies with ROH at our medical centre over an 8-year period.

METHODS

We report retrospective chart review data on 103 consecutive pregnancies from 2008 to 2015 with a median follow-up of 554 days.

RESULTS

After ROH diagnosis, 38 families opted for TOP. This decision was associated with onset of ROH (p < 0.001), underlying renal disease (p = 0.001) and presence of extrarenal manifestations (p = 0.02). Eight infants died in utero and 8 cases were lost to follow-up. Of the 49 liveborn children, 11 received palliative and 38 underwent active care. Overall survival of the latter group was 84.2% (n = 32) corresponding to 31% of all pregnancies (32 out of 103) analysed. One third of the surviving infants needed renal replacement therapy during the first 6 weeks of life.

CONCLUSIONS

Over one third of pregnancies with ROH were terminated and the parental decision was based on risk factors associated with adverse outcome. Neonatal death was rare in the actively treated infants and the overall outcome promising. Our study illustrates that only careful analysis of the whole process, from prenatal diagnosis via parental decision-making to postnatal outcome, allows sensible interpretation of outcome data.

Advances in the Understanding and Treatment of Mitochondrial Fatty Acid Oxidation Disorders

Purpose of review

This review focuses on advances made in the past three years with regards to understanding the mitochondrial fatty acid oxidation (FAO) pathway, the pathophysiological ramifications of genetic lesions in FAO enzymes, and emerging therapies for FAO disorders.

Recent findings

FAO has now been recognized to play a key energetic role in pulmonary surfactant synthesis, T-cell differentiation and memory, and the response of the proximal tubule to kidney injury. Patients with FAO disorders may face defects in these cellular systems as they age. Aspirin, statins, and nutritional supplements modulate the rate of FAO under normal conditions and could be risk factors for triggering symptoms in patients with FAO disorders. Patients have been identified with mutations in the ACAD9 and ECHS1 genes, which may represent new FAO disorders. New interventions for long-chain FAODs are in clinical trials. Finally, post-translational modifications that regulate fatty acid oxidation protein activities have been characterized that represent important new therapeutic targets.

Summary

Recent research has led to a deeper understanding of FAO. New therapeutic avenues are being pursued that may ultimately cause a paradigm shift for patient care.