SUCLA2 Arg407Trp mutation can cause a nonprogressive movement disorder - deafness syndrome

Two novel SUCLA2 variants cause mitochondrial DNA depletion syndrome, type 5 in two siblings

Mitochondrial DNA depletion syndrome (MDS), characterized by succinate-CoA ligase deficiency and loss of mitochondrial DNA (mtDNA), is caused by specific variants in nuclear genes responsible for mtDNA maintenance. SUCLA2-related mitochondrial DNA depletion syndrome, type 5 (MTDPS-5), presents as a rare, severe early progressive encephalomyopathy. This report investigates a new family exhibiting clinical manifestations of MTDPS-5 and elucidates the genetic basis of this disorder. In two affected siblings, a novel maternally inherited nonsense variant [c.1234C>T (p.Arg412*)] in the SUCLA2 gene and a unique paternally inherited indel variant (g.48569263-48571020del1758insATGA) were identified. Additionally, the siblings exhibited blood mtDNA content lower than 33% compared to age-matched controls. These findings underscore the importance of assessing SUCLA2 variants in patients with severe early progressive encephalomyopathy, even in the absence of methylmalonic aciduria or mtDNA loss, thereby broaden the mutational spectrum of this gene.

Metabolomics and transcriptomics of embryonic livers reveal hypoxia adaptation of Tibetan chickens

BACKGROUND

Exploring the hypoxia adaptation mechanism of Tibetan chicken is of great significance for revealing the survival law of Tibetan chicken and plateau animal husbandry production. To investigate the hypoxia adaptation of Tibetan chickens (TBCs), an integrative metabolomic-transcriptomic analysis of the liver on day 18 of embryonic development was performed. Dwarf laying chickens (DLCs), a lowland breed, were used as a control.

RESULTS

A total of 1,908 metabolites were identified in both TBCs and DLCs. Energy metabolism and amino acid metabolism related differentially regulated metabolites (DRMs) were significantly enriched under hypoxia. Important metabolic pathways including the TCA cycle and arginine and proline metabolism were screened; PCK1, SUCLA2, and CPS1 were found to be altered under hypoxic conditions. In addition, integrated analysis suggested potential differences in mitochondrial function, which may play a crucial role in the study of chicken oxygen adaptation.

CONCLUSIONS

These results suggest that hypoxia changed the gene expression and metabolic patterns of embryonic liver of TBCs compared to DLCs. Our study provides a basis for uncovering the molecular regulation mechanisms of hypoxia adaptation in TBCs with the potential application of hypoxia adaptation research for other animals living on the Qinghai-Tibet plateau, and may even contribute to the study of diseases caused by hypoxia.

Transcriptomics and metabolomics study in mouse kidney of the molecular mechanism underlying energy metabolism response to hypoxic stress in highland areas

Exposure to hypoxia disrupts energy metabolism and induces inflammation. However, the pathways and mechanisms underlying energy metabolism disorders caused by hypoxic conditions remain unclear. In the present study, a hypoxic animal model was created and transcriptomic and non-targeted metabolomics techniques were applied to further investigate the pathways and mechanisms of hypoxia exposure that disrupt energy metabolism. Transcriptome results showed that 3,007 genes were significantly differentially expressed under hypoxic exposure, and Gene Ontology annotation analysis and Kyoto Encyclopaedia of Genes and Genomes (KEGG) enrichment analysis showed that the differentially expressed genes (DEGs) were mainly involved in energy metabolism and were significantly enriched in the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) pathway. The DEGs IDH3A, SUCLA2, and MDH2 in the TCA cycle and the DEGs NDUFA3, NDUFS7, UQCRC1, CYC1 and UQCRFS1 in the OXPHOS pathway were validated using mRNA and protein expression, and the results showed downregulation. The results of non-targeted metabolomics showed that 365 significant differential metabolites were identified under plateau hypoxia stress. KEGG enrichment analysis showed that the differential metabolites were mainly enriched in metabolic processes, such as energy, nucleotide and amino acid metabolism. Hypoxia exposure disrupted the TCA cycle and reduced the synthesis of amino acids and nucleotides by decreasing the concentration of cis-aconitate, α-ketoglutarate, NADH, NADPH and that of most amino acids, purines, and pyrimidines. Bioinformatics analysis was used to identify inflammatory genes related to hypoxia exposure and some of them were selected for verification. It was shown that the mRNA and protein expression levels of IL1B, IL12B, S100A8 and S100A9 in kidney tissues were upregulated under hypoxic exposure. The results suggest that hypoxia exposure inhibits the TCA cycle and the OXPHOS signalling pathway by inhibiting IDH3A, SUCLA2, MDH2, NDUFFA3, NDUFS7, UQCRC1, CYC1 and UQCRFS1, thereby suppressing energy metabolism, inducing amino acid and nucleotide deficiency and promoting inflammation, ultimately leading to kidney damage.

Succinyl-CoA Synthetase Dysfunction as a Mechanism of Mitochondrial Encephalomyopathy: More than Just an Oxidative Energy Deficit

Biallelic pathogenic variants in subunits of succinyl-CoA synthetase (SCS), a tricarboxylic acid (TCA) cycle enzyme, are associated with mitochondrial encephalomyopathy in humans. SCS catalyzes the interconversion of succinyl-CoA to succinate, coupled to substrate-level phosphorylation of either ADP or GDP, within the TCA cycle. SCS-deficient encephalomyopathy typically presents in infancy and early childhood, with many patients succumbing to the disease during childhood. Common symptoms include abnormal brain MRI, basal ganglia lesions and cerebral atrophy, severe hypotonia, dystonia, progressive psychomotor regression, and growth deficits. Although subunits of SCS were first identified as causal genes for progressive metabolic encephalomyopathy in the early 2000s, recent investigations are now beginning to unravel the pathomechanisms underlying this metabolic disorder. This article reviews the current understanding of SCS function within and outside the TCA cycle as it relates to the complex and multifactorial mechanisms underlying SCS-related mitochondrial encephalomyopathy.

Molecular genetic landscape of hereditary hearing loss in Pakistan

Approximately 14.5 million Pakistani individuals have a hearing loss and half of these cases may be due to genetic causes. Though significant progress has been made in uncovering genetic variants for recessively inherited nonsyndromic deafness, Pendred syndrome, and Usher syndromes, the same is not true for dominantly inherited hearing loss, most syndromic cases and deafness with complex inheritance patterns. Variants of 57 genes have been reported to cause nonsyndromic recessive deafness in Pakistan, though most are rare. Variants of just five genes GJB2, HGF, MYO7A, SLC26A4, and TMC1 together explain 57% of profound deafness while those of GJB2, MYO15A, OTOF, SLC26A4, TMC1, and TMPRSS3 account for 47% of moderate to severe hearing loss. In contrast, although variants of at least 39 genes have been implicated in different deafness syndromes, their prevalence in the population and the spectrum of mutations have not been explored. Furthermore, research on genetics of deafness has mostly focused on individuals from the Punjab province and needs to be extended to other regions of Pakistan. Identifying the genes and their variants causing deafness in all ethnic groups is important as it will pinpoint rare as well as recurrent mutations. This information may ultimately help in offering genetic counseling and future treatments.