Orphanet Journal of Rare Diseases | Application of Animal Models in Methylmalonic Acidemia Research: New Advances and Challenges

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This article systematically reviews the research advances in animal models of methylmalonic acidemia (MMA), focusing on the advantages and limitations of different models and their potential applications in exploring disease mechanisms and therapeutic strategies, providing an important theoretical foundation for future clinical translational research.

 

Literature Overview
The article 'Application of Animal Models in Methylmalonic Acidemia Research: New Advances and Challenges' published in the Orphanet Journal of Rare Diseases reviews and summarizes the pathogenesis, animal model construction strategies, and their roles in disease research and therapeutic development. It details the genetic heterogeneity, biochemical pathway disruptions, and clinical manifestations of MMA, and systematically summarizes the applications of mutant mouse and zebrafish models constructed in recent years to simulate metabolic abnormalities and neurological lesions observed in patients.

Background Knowledge
MMA is an autosomal recessive organic acid metabolism disorder primarily caused by mutations in genes encoding methylmalonyl-CoA mutase (MCM) or its cofactor adenosylcobalamin (Ado-Cbl) synthesis enzymes. The disease leads to impaired methylmalonyl-CoA metabolism, resulting in the accumulation of toxic metabolites in the blood and causing severe neurological and systemic damage. Despite recent advances in diagnostic technologies (e.g., tandem mass spectrometry) and treatment options (e.g., low-protein diet, coenzyme Q10, liver transplantation), the high mortality during acute episodes and chronic neurological sequelae remain major clinical challenges. Animal models play an irreplaceable role in MMA research, particularly in disease mechanism elucidation, drug screening, and therapeutic evaluation. Currently, mouse models are commonly used, but high embryonic lethality and short lifespan limit their utility in long-term studies. In addition, some models rely on exogenous organic acid injections and fail to fully recapitulate systemic metabolic disturbances caused by genetic defects. Therefore, developing stable, viable, and predictable animal models has become a key research direction.

 

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Research Methods and Experiments
The article reviews the construction methods of MMA animal models, including gene knockout (e.g., CRISPR/Cas9), transgenic overexpression, and models incorporating patient-specific mutations. For example, Mut-/- mice, which completely lack MCM, die within 24 hours after birth, limiting their use in long-term studies. By introducing the FVB/N genetic background, researchers successfully extended the lifespan of Mut-/- mice, enabling studies of pathogenic mechanisms before weaning. Additionally, tissue-specific MMA models (e.g., Mut-/-;TgINS-Alb-Mut) constructed using liver- or muscle-specific promoters can assess contributions of different tissues to metabolic disturbances.

In zebrafish models, MMUT-deficient zebrafish constructed via CRISPR/Cas9 successfully recapitulate mitochondrial lesions in liver and kidney, behavioral abnormalities, and oxidative stress in MMA. A low-protein diet partially alleviates these phenotypes. This model has also been used for drug screening, where Mito-Q was shown to improve mitochondrial function and reduce disease phenotypes.

Key Findings and Perspectives

• Animal models of MMA are essential for studying metabolic disturbances, neurological damage, and therapeutic strategies.
• Mutant mouse models (e.g., Mut-/-) can mimic neonatal lethal phenotypes but have short lifespans, limiting chronic-phase studies.
• Genetic background modifications or tissue-specific expression can extend model survival, enabling long-term observation and therapeutic evaluation.
• CRISPR/Cas9 technology significantly improves model construction efficiency, especially for introducing high-frequency mutations (e.g., c.80A>G and c.609G>A).
• Zebrafish models are valuable for high-throughput drug screening and developmental studies due to their rapid development, transparent embryos, and ease of manipulation.
• Systemic genetic interventions in animal models have limitations; future studies should combine tissue-specific Cre mice or viral vector delivery to more accurately mimic localized disease manifestations.
• Large animal models (e.g., pigs, non-human primates) show potential for evaluating therapeutic approaches such as organ transplantation.
• Multi-omics integrated analysis and organoid technologies will provide a more comprehensive understanding of disease mechanisms and therapeutic targets.

Significance and Future Directions
Animal models hold irreplaceable value in MMA research, particularly in uncovering genotype-phenotype correlations and testing novel therapies (e.g., gene therapy, mRNA-based treatments). Future models should have longer lifespans and phenotypes more closely resembling patient subtypes to support long-term therapeutic interventions and pathological studies. Establishing models matched to patient mutation profiles, optimizing cobalamin treatment dosage-response curves, and exploring tissue-specific pathogenic mechanisms will be critical for enhancing translational relevance. The continuous optimization of animal models and integration of multi-omics data will bring new hope for MMA therapy.

 

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Conclusion
Methylmalonic acidemia (MMA) is a complex metabolic disorder caused by mutations in genes encoding methylmalonyl-CoA mutase (MCM) or its cofactor synthesis enzymes (e.g., MMACHC), with highly variable clinical manifestations and significant challenges in diagnosis and treatment. Animal models serve as a critical bridge between basic research and clinical translation, playing a central role in studying disease mechanisms, drug screening, and validating therapeutic strategies. Although several mouse and zebrafish models have successfully recapitulated certain MMA phenotypes, most suffer from early lethality, incomplete phenotypes, or failure to reflect tissue-specific pathology. Future studies should integrate conditional gene editing, large animal models, organoids, and organ-on-a-chip technologies to more accurately simulate disease progression and advance precision therapeutic strategies. Furthermore, model construction should focus on matching common patient mutations (e.g., c.80A>G, c.609G>A) to enhance translational potential. Continuous optimization of animal models and integration of multi-omics data will open new avenues for MMA treatment.

 

Shan Shan, Min Liu, Yue Ma, Yue Wang, and Hui Zou. Animal models of methylmalonic acidemia: insights and challenges. Orphanet Journal of Rare Diseases.