What methods are used to diagnose complex V deficiencies?

Sourav PanOctober 11, 2024

Answered

Diagnosing complex V deficiencies, which are part of the oxidative phosphorylation (OXPHOS) disorders, involves a combination of clinical evaluation, biochemical assays, and genetic testing. Here are the primary methods used for diagnosis:

1. Clinical Evaluation

• Patient History and Symptoms: A thorough clinical assessment is conducted, including a detailed patient history and evaluation of symptoms. Symptoms of complex V deficiency can vary widely and may include neurological issues, muscle weakness, and metabolic disturbances.

2. Biochemical Analysis

• Mitochondrial Biochemical Diagnostics: The most common method for diagnosing complex V deficiency is through mitochondrial enzyme assays. This involves:
  • Muscle Biopsy: A small sample of muscle tissue is obtained and analyzed for the activity of the OXPHOS complexes, including complex V. The activity levels of complex V are compared to normal ranges to identify deficiencies.
  • Respiratory Chain Enzyme Activity: The activities of all five OXPHOS complexes (I to V) are typically measured in muscle or fibroblast samples. A significant reduction in complex V activity indicates a deficiency 6.

3. Genetic Testing

• Molecular Genetic Analysis: Genetic testing is performed to identify mutations in the nuclear or mitochondrial DNA that are associated with complex V deficiency. This can include:
  • Next-Generation Sequencing (NGS): This method allows for the simultaneous analysis of multiple genes associated with mitochondrial function, including those encoding subunits of complex V and assembly factors.
  • Targeted Gene Panels: Specific panels can be designed to test for known mutations in genes related to complex V assembly and function 1.

4. Imaging Studies

• Magnetic Resonance Imaging (MRI): In some cases, MRI may be used to assess neurological involvement, especially if there are signs of encephalopathy or other central nervous system symptoms.

5. Metabolic Testing

• Lactate and Pyruvate Levels: Blood tests may be conducted to measure lactate and pyruvate levels. Elevated levels of these metabolites can indicate mitochondrial dysfunction, including complex V deficiency, as a result of impaired ATP production and increased anaerobic metabolism.

6. Functional Assays

• Cellular Respiration Studies: In some cases, fibroblasts or other cell types may be cultured, and their respiratory function can be assessed using high-resolution respirometry. This allows for the evaluation of mitochondrial respiration and ATP production in response to various substrates and inhibitors.