Mitochondrial (Maternal) Inheritance Patterns
| Feature | Genetic & Clinical Characteristics |
|---|---|
| Uniparental Transmission | Inherited exclusively from the mother. Mitochondria in the zygote are derived almost entirely from the oocyte; sperm-derived mitochondria are typically degraded post-fertilization. |
| Pedigree Pattern | Affected females pass the condition to all offspring (both sons and daughters). Affected males do not pass the condition to any of their children. |
| Heteroplasmy | The presence of both wild-type and mutated mitochondrial DNA (mtDNA) within the same cell. The severity of the disease often correlates with the proportion of mutated mtDNA inherited. |
| Variable Expressivity | Clinical presentation is highly variable within families due to the random distribution of mutated mitochondria during cell division (the bottleneck effect). |
High-Yield Core Realities:
- Tissue-Specific Vulnerability: Mitochondrial disorders most commonly manifest in tissues with high metabolic demand, such as the central nervous system (brain), skeletal muscle, and the heart (e.g., myopathies, encephalopathies).
- Clinical Examples:
- Leber Hereditary Optic Neuropathy (LHON),
- Myoclonic Epilepsy with Ragged Red Fibers (MERRF), and
- Mitochondrial Encephalomyopathy with Lactic Acidosis and
- Stroke-like episodes (MELAS).
- mtDNA Features: Unlike nuclear DNA, the mitochondrial genome is circular, lacks introns, and has a significantly higher mutation rate due to its proximity to the respiratory chain’s free radical production and its limited repair mechanisms.
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