Decoding mitochondrial disorders using Saccharomyces cerevisiae

NGS has revolutionized the identification of novel pathogenic mutations and disease-associated genes. However, once putative mutations are identified, their role in disease etiology must be confirmed through in vivo or in vitro functional studies. The yeast Saccharomyces cerevisiae is a powerful model for the validation and characterization of novel allelic variants, especially for mitochondrial disorders. Its ability to grow on fermentable or non-fermentable carbon sources and to survive without mitochondrial DNA (mtDNA) makes it particularly suitable for investigating mitochondrial function. This metabolic flexibility enables a comprehensive assessment of mitochondrial dysfunction by examining multiple parameters, including oxidative growth and respiratory activity, as well as more specific measurements such as the enzymatic activity of respiratory chain complexes, steady-state levels of the protein products, in vivo mtDNA maintenance, and mitochondrial protein synthesis. For some genes, another important advantage is the possibility of generating strains carrying the human gene instead of its yeast ortholog. We present selected examples showing how the yeast model clarifies the impact of mutations on protein function and phenotype: studying BCS1L and MTO1 genes we confirmed the pathogenicity of new mutations, whereas for LARS2 we excluded variants as disease-causing. We also describe different results when mutations in ACO2 have been studied either through homologous expression or heterologous expression. Validation of allelic variant is essential for diagnosis and therapy. Identifying a pathogenic mutation helps clinicians focus on a specific cause or exclude alternatives. Confirming pathogenicity and inheritance also supports genetic counseling and informed family planning.