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Clinical Manifestation of Mitochondrial Disorders in Childhood
Published in Shamim I. Ahmad, Handbook of Mitochondrial Dysfunction, 2019
MNGIE syndrome is an autosomal recessive progressive multisystem disease due to thymidine phosphorylase deficiency and by homozygous or compound heterozygous pathogenic mutations in TYMP gene. An excess of thymidine is damaging to mtDNA and causes mtDNA depletion, deletion, and point mutations (Taanman et al., 2009). Molecular genetic studies reveal multiple deletions of mitochondrial DNA (mtDNA) (Honzík et al., 2006).
Laboratory testing for mitochondrial diseases: biomarkers for diagnosis and follow-up
Published in Critical Reviews in Clinical Laboratory Sciences, 2023
Abraham J. Paredes-Fuentes, Clara Oliva, Roser Urreizti, Delia Yubero, Rafael Artuch
In recent years, it has been shown that non-coding RNAs (ncRNAs) are linked to multiple human diseases (such as cancer and Alzheimer’s disease) and that they also play a role in MDs [95–98]. ncRNAs, which perform their functions without being translated into proteins, include long ncRNAs with a plethora of regulatory actions, ribosomal RNAs (primary components of the ribosome and mitoribosome), transfer RNAs [99], and other regulatory RNAs such as microRNAs (miRNAs, see below), piRNAs, and siRNAs. As WES has some limitations in the capture of the coding regions prior to sequencing and most ncRNAs are not included in most commercial capture kits, WGS allows the identification of variants in all types of ncRNAs. miRNAs are small, highly conserved RNAs that control gene expression in a sequence-dependent manner. They act by binding directly to target mRNAs, with consequent target-mRNA degradation and/or translational repression, and they are involved in the regulation of a number of cellular processes [100,101]. Distinctive miRNA patterns have been associated with certain MDs, although the involvement of miRNAs in these diseases is only beginning to be understood. Meseguer et al. reported that miRNA-9/9* was induced through a reactive oxygen species/NFkB signaling pathway in MELAS syndrome and in myoclonic epilepsy with ragged-red fibers syndrome cybrid cells [100]. Yong et al. reported 55 significantly upregulated and 65 significantly downregulated miRNAs, all of which were implicated in various mitochondrial dynamics from a family with MNGIE syndrome [102]. Finally, Wang et al. found that miR-27b-3p was reduced in muscle and serum samples of MELAS syndrome patients with A3243G mutations or non-A3243G mutations and proposed the use of serum levels of this miRNA as a novel, non-invasive biomarker for MELAS syndrome [103].