With autosomal recessive inheritance, both parents carry a single defective copy of the gene and also a healthy gene.
The normal gene in a carrier usually supplies enough normal protein to avoid the signs and symptoms of the disease.
With each pregnancy a carrier of a defective gene has a 50% (one in two) chance of passing the mutated gene to the child. If the child inherits the altered gene, he or she will also be a carrier.
When both parents are carriers, there is a 25% (1 in 4) chance in every pregnancy that the child will inherit two mutated genes and will, therefore, have the disease.
There is also a 25% chance that the child will inherit two normal genes and will not have the disease nor be a carrier.
There is a 50% chance that the child will inherit one mutated gene and will be a carrier which may have implications for future generations.
Mitochondrial Diseases that can be inherited in this way include Leigh Syndrome, Alpers, MIRAS, SANDO, CPEO
With dominant inheritance, only one copy of the defective gene is required in order to develop Mitochondrial Disease. This means that each person with the disorder has a 50/50 chance of passing on the gene to any children they may have.
Additionally, any child that inherits the defect may develop the disorder and in turn have a 50/50 chance of passing on the defective gene.
However, with one normal and one mutated gene, all of these individuals may or may not develop symptoms of disease.
If they do develop disease, the severity can vary markedly. In regards to the highly variable manifestations among individuals with a defective gene, autosomal dominant and maternally inherited mitochondrial disorders are similar. However, in autosomal dominant, but never in maternally inherited conditions, boys can pass the defective gene and disease to their children.
Mitochondrial Diseases that can be inherited in this way include late onset CPEO.
In X-linked disease, the genetic defect is located on the "X" chromosome and usually affects males only.
This happens because females have 2 X chromosomes - 1 each from the mother and father, whereas males only have one X chromosome, inherited from their mother (they get a "Y" chromosome from their father).
Females with one normal X chromosome and one mutated X chromosome generally do not manifest the disorder because of the presence of the normal gene. However, these females are at risk for passing on genetic disease and are thus called "carriers".
On the other hand, since a male only has one X chromosome, if it is mutated he has no normal copy and will develop the disorder represented by the genetic defect.
If a female carrier has children, there is a 50/50 chance that she will pass on the defective gene to her children. If that child happens to be a girl and inherits the gene, she too will become a carrier.
If the child is a boy and inherits the defective gene, he will develop the disease.
Pyruvate Dehydrogenase Deficiency (E1alpha) is inherited this way.
Back to top