Case report: Two unexpected cases of DGUOK-related mitochondrial DNA depletion syndrome presenting with hyperinsulinemic hypoglycemia

Timely diagnosis of persistent neonatal hypoglycemia is critical to prevent neurological sequelae, but diagnosis is complicated by the heterogenicity of the causes. We discuss two cases at separate institutions in which clinical management was fundamentally altered by the results of molecular genetic testing. In both patients, critical samples demonstrated hypoketotic hypoglycemia and a partial glycemic response to glucagon stimulation, thereby suggesting hyperinsulinism (HI). However, due to rapid genetic testing, both patients were found to have deoxyguanosine kinase (DGUOK)-related mitochondrial DNA depletion syndrome, an unexpected diagnosis. Patients with this disease typically present with either hepatocerebral disease in the neonatal period or isolated hepatic failure in infancy. The characteristic features involved in the hepatocerebral form of the disease include lactic acidosis, hypoglycemia, cholestasis, progressive liver failure, and increasing neurologic dysfunction. Those with isolated liver involvement experience hepatomegaly, cholestasis, and liver failure. Although liver transplantation is considered, research has demonstrated that for patients with DGUOK-related mitochondrial DNA depletion syndrome and neurologic symptoms, early demise occurs. Our report advocates for the prompt initiation of genetic testing in patients presenting with persistent neonatal hypoglycemia and for the incorporation of mitochondrial DNA depletion syndromes in the differential diagnosis of HI

Biallelic variants in OGDH encoding oxoglutarate dehydrogenase lead to a neurodevelopmental disorder characterized by global developmental delay, movement disorder, and metabolic abnormalities

PURPOSE: This study aimed to establish the genetic cause of a novel autosomal recessive neurodevelopmental disorder characterized by global developmental delay, movement disorder, and metabolic abnormalities. METHODS: We performed a detailed clinical characterization of 4 unrelated individuals from consanguineous families with a neurodevelopmental disorder. We used exome sequencing or targeted-exome sequencing, cosegregation, in silico protein modeling, and functional analyses of variants in HEK293 cells and Drosophila melanogaster, as well as in proband-derived fibroblast cells. RESULTS: In the 4 individuals, we identified 3 novel homozygous variants in oxoglutarate dehydrogenase (OGDH) (NM_002541.3), which encodes a subunit of the tricarboxylic acid cycle enzyme α-ketoglutarate dehydrogenase. In silico homology modeling predicts that c.566C>T:p.(Pro189Leu) and c.890C>A:p.(Ser297Tyr) variants interfere with the structure and function of OGDH. Fibroblasts from individual 1 showed that the p.(Ser297Tyr) variant led to a higher degradation rate of the OGDH protein. OGDH protein with p.(Pro189Leu) or p.(Ser297Tyr) variants in HEK293 cells showed significantly lower levels than the wild-type protein. Furthermore, we showed that expression of Drosophila Ogdh (dOgdh) carrying variants homologous to p.(Pro189Leu) or p.(Ser297Tyr), failed to rescue developmental lethality caused by loss of dOgdh. SpliceAI, a variant splice predictor, predicted that the c.935G>A:p.(Arg312Lys)/p.(Phe264_Arg312del) variant impacts splicing, which was confirmed through a mini-gene assay in HEK293 cells. CONCLUSION: We established that biallelic variants in OGDH cause a neurodevelopmental disorder with metabolic and movement abnormalities

Biallelic variants in OGDH encoding oxoglutarate dehydrogenase lead to a neurodevelopmental disorder characterized by global developmental delay, movement disorder, and metabolic abnormalities

Purpose: This study aimed to establish the genetic cause of a novel autosomal recessive neurodevelopmental disorder characterized by global developmental delay, movement disorder, and metabolic abnormalities.Methods: We performed a detailed clinical characterization of 4 unrelated individuals from consanguineous families with a neurodevelopmental disorder. We used exome sequencing or targeted-exome sequencing, cosegregation, in silico protein modeling, and functional analyses of variants in HEK293 cells and Drosophila melanogaster, as well as in proband-derived fibroblast cells.Results: In the 4 individuals, we identified 3 novel homozygous variants in oxoglutarate dehydrogenase (OGDH) (NM_002541.3), which encodes a subunit of the tricarboxylic acid cycle enzyme alpha-ketoglutarate dehydrogenase. In silico homology modeling predicts that c.566C > T:p.(Pro189Leu) and c.890C > A:p.(Ser297Tyr) variants interfere with the structure and function of OGDH. Fibroblasts from individual 1 showed that the p.(Ser297Tyr) variant led to a higher degradation rate of the OGDH protein. OGDH protein with p.(Pro189Leu) or p.(Ser297Tyr) variants in HEK293 cells showed significantly lower levels than the wild-type protein. Furthermore, we showed that expression of Drosophila Ogdh (dOgdh) carrying variants homologous to p.(Pro189Leu) or p.(Ser297Tyr), failed to rescue developmental lethality caused by loss of dOgdh. SpliceAI, a variant splice predictor, predicted that the c.935G > A:p.(Arg312Lys)/p.(Phe264_Arg312del) variant impacts splicing, which was confirmed through a mini-gene assay in HEK293 cells.Conclusion: We established that biallelic variants in OGDH cause a neurodevelopmental disorder with metabolic and movement abnormalities.(c) 2022 The Authors. Published by Elsevier Inc. on behalf of American College of Medical Genetics and Genomics. This is an open access article under the CC BY licensePeer reviewe

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Whole Epigenome Pattern Characterization in CMML and Related Monocytoid Malignancies

Abstract Abstract 599 Aberrant epigenetic silencing of genes through aberrant promoter hypermethylation, as occurs with tumor suppressor genes (TSG), has been implicated in the pathogenesis of MDS and other myeloid malignancies and has been clinically targeted by hypomethylating agents. To date, most of the studies investigating hypermethylation of TSG in hematologic malignancies targeted empirically selected gene promoters but with the advent of methylation arrays, global analysis of methylation pattern became technically possible. We applied methylation arrays (Illumina ®) allowing for simultaneous analysis of 25K CpG sites, focusing on the WHO defined subentity of MDS/MPD, CMML, because of possible efficacy of hypomethylating agents in this disease and the need to identify diagnostic markers and predictors of response. We hypothesized that by comparing CMML patients to patients with similar monocytoid entities, we would be able to establish an epigenetic signature that was consistent across these diagnoses. We studied patients with CMML (N=26), JMML (N=22) and monocytoid forms primary AMLs (N=16; M4 N=9 and M5 N=7) to controls (N=28). In addition we studied 35 patients with advanced and 37 low risk MDS and 9 with MDS/MPN. We developed an analytic algorithm that included establishment of the methylome of normal marrow to define normal/physiologic methylation status for each of CpG islands. These parameters were used as a reference for analysis of concordantly hypermethylated genes in patients, using methylation status as either a continuous (β, where β is proportional to the percentage of cells with methylated status at the locus) or dichotomized variable (where hypermethylation was defined as a β-value greater than the 97th percentile of controls). Each disease was individually compared with controls in order to establish genes aberrantly hypermethylated within the specific entity and the established methylome of each entity was compared with that of other entities. As expected, comparison of the average methylation level across all genes showed no significant differences between groups. Among all subgroups, there were only 58 genes that were consistently hypermethylated; the majority of genes were uniquely hypermethylated in each of the disease subgroups. When CMML and JMML were examined as exemplary conditions, global methylation analysis demonstrated that there was concordant hypermethylation in 25%, 50% and 75% of CMML patients in 1086, 13 and 0 CpG sites, respectively. In contrast, there was a great deal of concordant methylation in JMML with 3796, 1006, 176 of methylated promoters concordant in 25%, 50% and 75% of patients, respectively. The genes that were the most consistently hypermethylated in each entity were selected for further analysis. In JMML, the most consistently hypermethyated genes included LHX6, CDK10, ITGA2B and RAP1GA1. These genes were differentially hypermethylated in JMML compared to CMML (p<.0001 for each gene). In CMML, examples of the most consistently hypermethylated promoters included RPL36, BCORL, GPR171 and HAPLN1; hypermethylation of GPR171 and HAPLN1 clearly distinguished CMML from JMML (p<.0001, p=.0075, respectively.) GPR171 was hypermethylated in significantly more CMML patients than patients with M4 and M5 (p<.0001). In contrast, HAPLN1 was hypermethylated in more patients with M4 and M5 than with CMML (87% of patients). This finding led us to speculate that methylation of HAPLN1 may be a marker associated with disease progression. In fact, HAPLN1 was hypermethylated in 67% of patients with CMML1, compared with 78% of patients with CMML2. We also compared the whole epigenome profile of each subentity to each other. We selected genes whose average methylation level in a disease entity was greater than the cutoff of 2 standard deviations above the mean of controls. This resulted in selection of 550 genes in CMML patients, of which 230 were also part of the conserved epigenetic pattern of M4, while only 146 were part of the conserved epigenetic pattern of M5. M4 and M5 showed more similarity with each other, sharing 355 genes within their epigenetic profiles. In conclusion there are few shared epigenetic changes among the monocytoid/ myelomonocytoid malignancies; however, epigenetic changes in these entities are largely unique to each entity. These data suggest that methylation analysis may be useful to supplement histomorphologic diagnostic criteria in distinguishing between these monocytoid malignancies. Disclosures: No relevant conflicts of interest to declare

The Importance of Succinylacetone: Tyrosinemia Type I Presenting with Hyperinsulinism and Multiorgan Failure Following Normal Newborn Screening

Tyrosinemia type I (TT1) is an inborn error of tyrosine metabolism with features including liver dysfunction, cirrhosis, and hepatocellular carcinoma; renal dysfunction that may lead to failure to thrive and bone disease; and porphyric crises. Once fatal in most infantile-onset cases, pre-symptomatic diagnosis through newborn screening (NBS) protocols, dietary management, and pharmacotherapy with nitisinone have improved outcomes. Succinylacetone provides a sensitive and specific marker for the detection of TT1 but is not universally utilized in screening protocols for the disease. Here, we report an infant transferred to our facility for evaluation and management of hyperinsulinism who subsequently developed acute-onset liver, respiratory, and renal failure around one month of life. She was found to have TT1 caused by novel pathogenic variant in fumarylacetoacetate hydrolase (c.1014 delC, p.Cys 338 Ter). Her NBS, which utilized tyrosine as a primary marker, had been reported as normal, with a tyrosine level of 151 &micro;mol/L (reference: &lt;280 &micro;mol/L). Retrospective analysis of dried blood spot samples via tandem mass spectrometry showed detectable succinylacetone ranging 4.65&ndash;10.34 &micro;mol/L. To our knowledge, this is the first patient with TT1 whose initial presenting symptom was hyperinsulinemic hypoglycemia. The case highlights the importance of maintaining a high suspicion for metabolic disease in critically ill children, despite normal NBS. We also use the case to advocate for NBS for TT1 using succinylacetone quantitation