• For many patients, mitochondrial disease is an inherited genetic condition. Mutations can also be spontaneous as well as be induced.
• A patient may be found to have a de novo variant, or new mutation, meaning that the mutation arose in this patient early in development and was not passed down from a parent or previous generations.
• An uncertain percentage of patients acquire symptoms due to other factors, including mitochondrial toxins.
It is important to determine which type of mitochondrial disease inheritance is present in order to pre- dict the risk of recurrence for future children. The types of mitochondrial disease inheritance include:
Nuclear DNA (nDNA) inheritance:
- nDNA is contained in the nucleus of the cell. This type of inheritance is also called autosomal inheritance.
- If the gene trait is recessive (one gene needed from each parent to have the disease), often no other family members appear to be affected. Two recessive mutations, one from each parent, are needed to express the disease. If parents both share the same recessive gene for a particular type of mitochondrial disease, 25% of children will get both mutated genes and have the disease, 25% will get no mutated genes and be healthy, and 50% will get a single mutation and be considered a “carrier,” like their parents, also be healthy, but could pass the mutation to their offspring.
- If the gene trait is dominant (a gene from either parent can express disease), the disease often oc- curs in other family members. There is a 50 percent chance of the trait occurring in other siblings/ offspring.
- Mitochondrial DNA (mtDNA) inheritance. mtDNA is contained in the mitochondria of the cell.
- There is a 100 percent chance of the trait occurring in other siblings, since all mitochondria are inherited from the mother, although symptoms might be either more or less severe due to heteroplasmy (the percent of mutated cells). Higher rates of heteroplasmy are typically associated with more severe disease.
Combination of mtDNA and nDNA defects:
- The relationship between nDNA and mtDNA and their correlation in mitochondrial formation is a new area of study. MtDNA and nDNA communicate with each other. Researchers believe that such interactions may regulate the expression of particular sets of genes. This communication may ex- plain how mitochondria are involved in cellular processes not related to energy generation, such as cell growth and death.
- Diseases specifically from deletions of large parts of the mtDNA molecule are usually sporadic with- out affecting other family members.
- Medicines or other toxic substances can trigger mitochondrial disease.