Mutations in mitochondrial DNA appear to be responsible for a number of neurological disorders, including myoclonic epilepsy and ragged-red fiber disease, Leber's hereditary optic neuropathy, and Kearns-Sayre syndrome. In each case, the disease phenotype is expressed when the ratio of mutant to wild-type mitochondria exceeds a threshold peculiar to each disease, but usually in the 60 to 95 percent range.

Compared with the vast number of mitochondria in an embryo, the number of mitochondria in an ovum is relatively small. Might such an ooplasmic mitochondrial bottleneck present an opportunity for therapy or cure? Explain.

Key Concepts

Mitochondrial DNA and Mutations

Mitochondrial DNA (mtDNA) is distinct from nuclear DNA and is inherited maternally. Mutations in mtDNA can lead to various diseases, particularly affecting energy-intensive tissues like the nervous system. Understanding how these mutations impact mitochondrial function is crucial for grasping the underlying mechanisms of mitochondrial disorders.

Threshold Effect in Mitochondrial Diseases

The threshold effect refers to the phenomenon where a certain proportion of mutant mitochondria must be present for a disease phenotype to manifest. In mitochondrial disorders, this threshold typically ranges from 60% to 95% mutant mitochondria, meaning that below this level, the individual may remain asymptomatic despite carrying mutations.

Ooplasmic Mitochondrial Bottleneck

The ooplasmic mitochondrial bottleneck is a developmental stage in oocyte maturation where only a limited number of mitochondria are passed from the mother to the offspring. This bottleneck can create an opportunity for therapeutic interventions, as it may allow for the selection of healthier mitochondria, potentially reducing the transmission of mitochondrial diseases.