FDX2 and ISCU Gene Variations Lead to Rhabdomyolysis With Distinct Severity and Iron Regulation

Clinical, biochemical and molecular characterization of a new case with FDX2-related mitochondrial disorder: Potential biomarkers and treatment options

Ferredoxin-2 (FDX2) is an electron transport protein required for iron-sulfur clusters biosynthesis. Pathogenic variants in FDX2 have been associated with autosomal recessive FDX2-related disorder characterized by mitochondrial myopathy with or without optic atrophy and leukoencephalopathy. We described a new case harboring compound heterozygous variants in FDX2 who presented with recurrent rhabdomyolysis with severe episodes affecting respiratory muscle. Biochemical analysis of the patients revealed hyperexcretion of 2-hydroxyadipic acid, along with previously reported biochemical abnormalities. The proband demonstrated increased lactate and creatine kinase (CK) with increased amount of glucose infusion. Lactate and CK drastically decreased when parenteral nutrition containing high protein and lipid contents with low glucose was initiated. Overall, we described a new case of FDX2-related disorder and compare clinical, biochemical and molecular findings with previously reported cases. We demonstrated that 2-hydroxyadipic acid biomarker could be used as an adjunct biomarker for FDX2-related disorder and the use of parenteral nutrition as a treatment option for the patient with FDX2-related disorder during rhabdomyolysis episode.

Highlights

2-Hydroxyadipic acid can serve as a potential adjunct biomarker for iron-sulfur assembly defects and lipoic acid biosynthesis disorders. Parenteral nutrition containing high lipid and protein content could be used to reverse acute rhabdomyolysis episodes in the patients with FDX2-related disorder.

Α rare case of myopathy, lactic acidosis, and severe rhabdomyolysis, due to a homozygous mutation of the ferredoxin-2 (FDX2) gene

Mitochondrial myopathy is a severe metabolic myopathy related to nuclear or mitochondrial DNA dysfunction. We present a rare case of mitochondrial myopathy, presented with multiple episodes of proximal muscle weakness, lactic acidosis, and severe rhabdomyolysis (CPK 319,990 U/L, lactic acid 22.31 mmol/L, and GFR 3.82 mL/min/1.73m2 ). She was hospitalized in the pediatric intensive care unit due to acute kidney injury, elevated blood pressure, and deterioration of respiratory and cardiac function. Investigation for inherited metabolic disorders showed elevated levels of ammonia, lactic acid to pyruvic acid ratio, and urine ketone bodies. Exome sequencing detected a homozygous pathogenic variant in FDX2 (ENST00000541276:p.Met4Leu/c.10A > T) and a heterozygous variant of uncertain significance in MSTO1 (ENST00000538143:p.Leu137Pro/c.410 T > C). After Sanger sequencing, the p.Met4Leu pathogenic variant in FDX2 (ENST00000541276:p.Met4Leu/c.10A > T) was identified in a heterozygous state in both her parents and sister. Recently, pathogenic variants in the FDX2 gene have been associated with mitochondrial myopathy, lactic acidosis, optic atrophy, and leukoencephalopathy. Only four reports of FDX2-related rhabdomyolysis have been described before, but none of the previous patients had hyperammonemia. This is a rare case of severe mitochondrial myopathy in a pediatric patient related to a pathogenic FDX2 variant, suggesting the need for genetic analysis of the FDX2 gene in cases of suspicion of mitochondrial myopathies.

Intratumor microbiome derived glycolysis-lactate signatures depicts immune heterogeneity in lung adenocarcinoma by integration of microbiomic, transcriptomic, proteomic and single-cell data

Introduction

Microbiome plays roles in lung adenocarcinoma (LUAD) development and anti-tumor treatment efficacy. Aberrant glycolysis in tumor might promote lactate production that alter tumor microenvironment, affecting microbiome, cancer cells and immune cells. We aimed to construct intratumor microbiome score to predict prognosis of LUAD patients and thoroughly investigate glycolysis and lactate signature's association with LUAD immune cell infiltration.

Methods

The Cancer Genome Atlas-LUAD (TCGA-LUAD) microbiome data was downloaded from cBioPortal and analyzed to examine its association with overall survival to create a prognostic scoring model. Gene Set Enrichment Analysis (GSEA) was used to find each group's major mechanisms involved. Our study then investigated the glycolysis and lactate pattern in LUAD patients based on 19 genes, which were correlated with the tumor microenvironment (TME) phenotypes and immunotherapy outcomes. We developed a glycolysis-lactate risk score and signature to accurately predict TME phenotypes, prognosis, and response to immunotherapy.

Results

Using the univariate Cox regression analysis, the abundance of 38 genera were identified with prognostic values and a lung-resident microbial score (LMS) was then developed from the TCGA-LUAD-microbiome dataset. Glycolysis hallmark pathway was significantly enriched in high-LMS group and three distinct glycolysis-lactate patterns were generated. Patients in Cluster1 exhibited unfavorable outcomes and might be insensitive to immunotherapy. Glycolysis-lactate score was constructed for predicting prognosis with high accuracy and validated in external cohorts. Gene signature was developed and this signature was elevated in epithelial cells especially in tumor mass on single-cell level. Finally, we found that the glycolysis-lactate signature levels were consistent with the malignancy of histological subtypes.

Discussion

Our study demonstrated that an 18-microbe prognostic score and a 19-gene glycolysis-lactate signature for predicting prognosis of LUAD patients. Our LMS, glycolysis-lactate score and glycolysis-lactate signature have potential roles in precision therapy of LUAD patients.

Recent advances in our understanding of genetic rhabdomyolysis

PURPOSE OF REVIEW

This review summarizes recent advances in our understanding of the genetics of rhabdomyolysis.

RECENT FINDINGS

Rhabdomyolysis is the acute breakdown of myofibres resulting in systemic changes that can be life-threatening. Environmental triggers, including trauma, exercise, toxins and infections, and/or gene defects can precipitate rhabdomyolysis. A schema (aptly titled RHABDO) has been suggested for evaluating whether a patient with rhabdomyolysis is likely to harbour an underlying genetic defect. It is becoming increasingly recognized that defects in muscular dystrophy and myopathy genes can trigger rhabdomyolysis, even as the sole or presenting feature. Variants in genes not previously associated with human disease have been identified recently as causative of rhabdomyolysis, MLIP , MYH1 and OBSCN . Our understanding of the pathomechanisms contributing to rhabdomyolysis have also improved with an increased awareness of the role of mitochondrial dysfunction in LPIN1 , FDX2 , ISCU and TANGO2 -mediated disease.

SUMMARY

An accurate genetic diagnosis is important for optimal clinical management of the patient, avoiding associated triggers and genetic counselling and cascade screening. Despite recent advances in our understanding of the genetics contributing to rhabdomyolysis, many patients remain without an accurate genetic diagnosis, suggesting there are many more causative genes, variants and disease mechanisms to uncover.