Driver or amplifier? A new review grades where mitochondria truly cause brain disease — and where they pile on

Edited by Samael A. Tejada, Founder & Editor-in-Chief

The most useful word in this review is 'graded'. Mitochondria are involved in all four diseases; the review asks the harder question of what 'involved' actually earns, disease by disease.

How did the review grade causality?

The authors compared shared and disease-selective mitochondrial defects across AD, PD, ALS and HD, and graded the evidence supporting causality from three tiers: human genetics, patient tissue, and model systems. That ordering matters. A defect that appears in patient tissue but rests mainly on models earns a weaker causal claim than one anchored in human mutations — which is why the same organelle can be a driver in one disease and an amplifier in another. Mitochondrial dysfunction in Alzheimer's, for example, is detectable before clinical symptoms and accompanies amyloid-beta and tau pathology, but the supporting evidence there is largely observational or model-based rather than genetic.

What differs between the diseases?

In Parkinson's, the genetic anchors are direct: PINK1 and Parkin — core mitophagy genes — cause inherited forms of the disease, and complex I inhibition reproduces parkinsonian injury. In genetic ALS, SOD1 and C9orf72 mutations carry mitochondrial defects with them. In sporadic Alzheimer's, the review places mitochondria downstream of amyloid-beta and tau, which impair mitophagy — an early amplifier that worsens the proteinopathy's damage once it starts. In Huntington's, mutant huntingtin drives bioenergetic dysfunction, again positioning mitochondria as amplifiers of a toxicity that originates elsewhere. Shared mechanisms — oxidative phosphorylation failure, fission–fusion imbalance, failed axonal transport, ROS excess — run through all four, which is why single-mechanism drugs keep being tried across all of them.

Why haven't mitochondria-targeted brain therapies succeeded?

The review's translational section is the sobering part: mitochondria-targeted antioxidants, fusion and biogenesis enhancers, fission inhibitors, inflammasome modulators, mPTP inhibitors and gene therapies have produced a rich preclinical literature and, so far, no clinical success story in neurodegeneration. The newer directions it highlights — USP30 inhibition to boost mitophagy, intercellular mitochondrial transfer, and a regulatory-approved mitochondria-targeted peptide in another indication — show the field is still advancing, but the driver-versus-amplifier grading offers a possible explanation for past failures: an amplifier target treated as if it were the driver may simply be aimed at the wrong point in the causal chain. For readers, that framing is the practical takeaway — ask of any 'mitochondrial' brain therapy which disease, and which causal tier, its evidence actually sits on.

Where the evidence stands

• Established: Mitochondrial defects — oxidative phosphorylation failure, dynamics imbalance, defective mitophagy, impaired axonal transport and ROS excess — are documented features of AD, PD, ALS and HD; PINK1/Parkin mutations cause inherited Parkinson's.
• Preliminary: The causal grading itself: a narrative review's synthesis (2026) placing mitochondria as primary drivers in PD and genetic ALS and as early amplifiers in sporadic AD and HD. Reasonable experts can weight the tiers differently.
• Contested: Whether mitochondria-targeted therapies can succeed clinically in neurodegeneration: the review records no clinical success to date despite extensive preclinical work, with newer approaches still unproven in patients.