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A new mutation in one of the components of the complex IV of the respiratory chain responsible for MELAS syndrome
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MELAS syndrome is one of the mitochondrial diseases described mainly in adults. As its acronym suggests, it combines myopathy (M), encephalopathy (E), lactic acidosis (LA) and pseudo-stroke (S). To this complex and protean picture can be added cardiac complications of various types (abnormalities of myocardial contractility, conduction disorders, etc.). MELAS syndrome is transmitted by maternal inheritance and is due in the vast majority of cases to a one-time abnormality in the mitochondrial DNAmacromolécule complexe, l’ADN est le support de l’hérédité (gènes). C’est le constituant des chromosomes. L’ADN est organisé en double hélice (deux brins complémentaires) et constitué de nucléotides de quatre types : adénine, guanine, cytosine et thymine. (the 3243A> G mutationModification soudaine et transmissible du matériel génétique. Elle peut être spontanée ou induite par des agents dits » mutagènes » (radiations, produits toxiques,…).) encoding a transfer RNAmacromolécule constituée d’une seule chaîne de nucléotides (simple brin) résultant de la transcription (copie) de l’ADN.. Most of the time, these are sporadic cases.
In an article published in May 2021, Chinese clinicians associated with German geneticists report the observation of a young 12-year-old patient fulfilling all the diagnostic criteria in favor of a MELAS syndrome but whose genotype was found to be unprecedented. The sequencing of its mitochondrial DNA has indeed revealed the presence of a pathogenic variant in the MT-CO3 gene encoding one of the sub-elements of complex IV of the respiratory chain. Mutations in genes encoding complex proteins are exceptional. In the present case, additional functional studies, in particular from the study of cybrids, were necessary to confirm the pathogenicity of the variant.