Inheritance: Here's how it works, in a Ms. Pacman sort of way. : ) I got most of this information from Dr. Korson's slide presentation at UMDF Symposium, and this is my interpretation of the 5 ways you can get mito.

1. Happens in a small # of cases:
SPORADIC OCCURRENCE:
This is what I call the bad luck method of inheritance. It just pops up from nowhere. Interference in some genes causes mitochondrial dysfunction.

2. Estimated 25% (or so) of cases.

MATERNAL INHERITANCE:
Mitochondrial DNA (mtDNA) NOT nuclear (nDNA). So here, mom is affected. Mom passes it on to all kids. Daughters keep passing it on. Males get mito from mom, but they don't pass it on to offspring.

Phenotype in offspring with mtDNA mutations can be extremely variable, but there's usually an obvious pattern on mom's side.

3. Estimated 75% of mitochondrial disorders are caused by mitochondrial defects in the Nuclear DNA.

AUTOSOMAL RECESSIVE INHERITANCE:
Nuclear (nDNA) NOT Mitochondrial DNA (mtDNA). So here, parents are non-symptomatic carriers. 25% or 1 in 4 is the recurrence risk in every pregnancy.

4. Estimated 75% of mitochondrial disorders occur from mitochondrial defects in the Nuclear DNA.

AUTOSOMAL DOMINANT INHERITANCE:
Nuclear (nDNA) NOT Mitochondrial DNA (mtDNA). One parent has a dominant gene mutation and passes it on 50% of the time to boys and girls alike.

5. Estimated 75% of mitochondrial disorders occur from mitochondrial defects in the Nuclear DNA.

X-LINKED INHERITANCE:
Nuclear (nDNA) NOT Mitochondrial DNA (mtDNA). Carrier females pass on the affected gene to 1/2 offspring. The daughters of affected males are usually carriers.