Deep Sequencing Reveals Novel Genetic Variants in Children with Acute Liver Failure and Tissue Evidence of Impaired Energy Metabolism

Abstract

Background & AimsThe etiology of acute liver failure (ALF) remains elusive in almost half of affected children. We hypothesized that inherited mitochondrial and fatty acid oxidation disorders were occult etiological factors in patients with idiopathic ALF and impaired energy metabolism.MethodsTwelve patients with elevated blood molar lactate/pyruvate ratio and indeterminate etiology were selected from a retrospective cohort of 74 subjects with ALF because their fixed and frozen liver samples were available for histological, ultrastructural, molecular and biochemical analysis.ResultsA customized next-generation sequencing panel for 26 genes associated with mitochondrial and fatty acid oxidation defects revealed mutations and sequence variants in five subjects. Variants involved the genes ACAD9, POLG, POLG2, DGUOK, and RRM2B; the latter not previously reported in subjects with ALF. The explanted livers of the patients with heterozygous, truncating insertion mutations in RRM2B showed patchy micro- and macrovesicular steatosis, decreased mitochondrial DNA (mtDNA) content <30% of controls, and reduced respiratory chain complex activity; both patients had good post-transplant outcome. One infant with severe lactic acidosis was found to carry two heterozygous variants in ACAD9, which was associated with isolated complex I deficiency and diffuse hypergranular hepatocytes. The two subjects with heterozygous variants of unknown clinical significance in POLG and DGUOK developed ALF following drug exposure. Their hepatocytes displayed abnormal mitochondria by electron microscopy.ConclusionTargeted next generation sequencing and correlation with histological, ultrastructural and functional studies on liver tissue in children with elevated lactate/pyruvate ratio expand the spectrum of genes associated with pediatric ALF.

Phenotypic and Genotypic Heterogeneity of RRM2B Variants

“…Seven patients were reported by Bourdon et al, 2 but they included one patient, which has been reported earlier by Paqulis-Flucklinger et al 3 why only six of these patients were evaluated for phenotype analysis. Three patients were reported by Bornstein et al 4 Two patients each were reported by Kropach et al, 1 Pitceathly et al, 13 Spinazzola et al, 5 Kollberg et al, 6 and Valencia et al 12 One patient each was reported by Paqulis-Flucklinger et al, 3 Acham-Roschitz et al, 7 Stojanovic et al, 8 Hernández-Laín et al, 9 Shaibani et al, 11 Takata et al, 15 and by Wilichowksi et al 16 A single patient carrying a RRM2B variant was also reported by Horga et al 18 However, this case was excluded since no individual data were reported and since the case could have been included in the paper by Pitceathly et al 10 already. The paper by Wilichowski et al 16 was published only as an abstract so far (►Table 1).…”

“…RRM2B mutations have been reported in 82 patients in 18 publications so far (►Table 1). [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The largest number of patients (n ¼ 26) was reported in a paper by Pitceathly et al 10 but 11 of these patients were described as having been reported earlier, without detailing the particular publications in which these 10 patients have been mentioned (►Table 1). 10 Seventeen patients carrying a RRM2B mutation from two families were reported by Tyynismaa et al 2009.…”

“…Horga et al 18 for 2′-Desoxyribonucleosid-5′-triphosphate (dNTP) synthesis required for DNA repair and mitochondrial DNA (mtDNA) synthesis required for DNA repair and mitochondrial DNA (mtDNA) synthesis in nonproliferating cells. 12 Mutations in the RRM2B gene result in reduced or absent provision of dNTPs and secondary to mtDNA depletion or multiple mtDNA deletions. 19 Generally, mitochondrial disorders (MIDs) caused by dysfunction of the nuclear maintenance genes can be broadly classified into two groups: (1) mutations that cause mtDNA depletion, which are at the most severe end of the phenotypic spectrum and (2) mutations that predispose to accumulation of multiple mtDNA deletions.…”

“…Autosomal dominant (AD) or autosomal recessive (AR) mutations in the RRM2B gene cause a mitochondrial multiorgan disorder syndrome (MIMODS), so far reported to manifest mainly in the brain, kidneys, and skeletal muscles (►Table 1). [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Since the first description of the phenotype by Paquis-Flucklinger et al 1995 3 and the first detection of a RRM2B mutation by Bourdon et al in 2007, 2 an increasing number of mutations and increasing heterogeneity of the phenotype have been reported (►Tables 2 and 3). This review aims at summarizing recent advances con-cerning the genotypic and phenotypic variability of RRM2B mutations.…”

Drug rechallenge following drug‐induced liver injury

“…In addition to drug‐specific factors, susceptibility to DILI varies by patient. For example, children with mitochondrial polymorphisms/disorders are highly susceptible to drug‐induced acute liver failure and fatality . Furthermore, drug metabolism and immune response are influenced by concomitant medications, inflammation, and genetics .…”