Mitochondria
Characteristics of Genetic disorders caused by mitochondrial mutations
Dr.V.Malathi
- Both males and females are affected
- The condition is transmitted mostly through the female to her offspring
- If a male has the trait and his spouse does not then their offspring would not have the trait
- In case a mother has a disease caused by a mitochondrial mutation where she lacks normal mitochondria and have only abnormal, mutation-bearing ones then the affected mother will always pass on mutation-bearing mitochondria to her children.
- A mitochondrial disorder may occur when a person has a mix of normal and abnormal mitochondria her body. In this case, normal and mutation-bearing mitochondria may go randomly into eggs during meiosis. Children who get a large proportion of mutant mitochondria may have severe disease, while those with few mutant mitochondria may have mild or no disease
- The expression of mitochondrial conditions is variable. Inside each cell, there are several mitochondria. The number of mitochondria that carry the mutation can vary. Thus a cell can have a mixture of normal and abnormal mitochondrial genomes, which is referred to as heteroplasmy.In contrast, homoplasmy refers a state in which all copies of the mitochondrial genome carry the same sequence variant.
- A certain proportion of mutant mitochondria within a cell can be tolerated and the disease will not be expressed in the organism. A larger proportion of mutant mitochondria however, may cause the disease to be expressed in the organism.
- Unequal segregation of mitochondria carrying normal and abnormal genomes and replicative advantage can result in varying degrees of heteroplasmy in the cells of an affected individual, including the individual ova of an affected female. Because of this, a mother may be asymptomatic yet have children who are severely affected. The level of heteroplasmy at which disease symptoms typically appear can also vary based on the type of mitochondrial variant.
- The threshold of abnormal mitochondria needed for an abnormal phenotype is variable depending on the condition but in general is 60% to 90%.
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