Genetics Northern California

Mitochondrial Inheritance

Mitochondrial disorders are a group of genetic diseases that are inherited in a very unique way. Most of our DNA is found in the nucleus of our cells, organized as chromosomes. However, there is another kind of DNA that is found exclusively in organelles outside of the cell nucleus, called the mitochondria. Mitochondria are important because they provide much of the energy that is needed by cells to function properly. Mitochondria contain DNA separate from the DNA present in the nucleus. This DNA is inherited in a different pattern.

Mitochondrial disorders are generally passed from an affected mother to all of her children. This is because mitochondria are located inside the egg cells. The mitochondria present in sperm are concentrated in the tail and are not included inside the fertilized egg. Hence, a male with a mitochondrial disease is not at risk to have children affected with the disease.

Mitochondrial disorders may seem easy to identify in a family based upon the fact that all offspring of an affected mother will inherit the disorder. However, there is wide variability in the symptoms that appear in families with these types of disorders. For example: In a single disorder, there are families where some individuals develop strokes at a young age, others in the family have muscle weakness, and still others have an eye problem; yet they all carry the same problem with the mitochondrial DNA.