Genetic Diagnosis of Mitochondrial Diseases

Mitochondrial Diseases

Mitochondrial diseases are a group of heterogeneous diseases caused by dysfunction due to genetic mutations in the mitochondrial genome or mutations in the nuclear genome which has an effect on the structure, function and integrity of the mitochondria. 

Mitochondrial diseases occur at an estimated frequency of 1:2000 to 1:5000 individuals, making it one of the most commonest genetic diseases.

This high rate is largely contributed by the fact that mitochondria generates a lot of oxidative free radicals during the oxidative phosphorylation step and also lacks a robust proof reading mechanism for DNA replication.

Mitochondria are versatile organelles in the cell. The primary role of mitochondria in the cell is the production of energy. Therefore the mitochondria are popularly known as the powerhouses of the cell.
Mitochondrial genome
The mitochondria has a small genome, approximately over 16 kilobases in length and encodes for a handful of genes. The mitochondrial genome is known to encode for 37 genes.

While the mitochondrial genome only encodes for a small number of genes, the normal functioning of the mitochondria requires a number of gene products to be imported from the cytoplasm.

Mitochondrial genetic mutations

Mitochondria has a high mutation rate, approximately 100 times that of the nuclear genome.

Mutations which cause mitochondrial diseases are very well studied and catalogued. This encompass approx. 73 mtDNA functional loci and around 580 disease associations.

Mitochondria exhibit a unique property of hetroplasmy, which is defined as the existence of more than one type of organellar genetic material in a single mitochondria or in an individual.

Approximately about 90% of the individuals carry at least one heteroplasmic site and ~20% of the individuals harbour heteroplasmies reported to be implicated in disease.