MIDD - An Introduction

Maternally Inherited Diabetes with Deafness, MIDD, is a classification of patients who show the combined symptoms of Deafness and Diabetes, with a family history of these conditions on their mothers side.

This has been traced to a single defect in the genetic code of Mitochondrial DNA, (mtDNA).

Mitochondria are the "Power House" of the cell, converting the energy in glucose into energy that the cell can use. The genetic defect causes a small problem in creating the proteins used in the Mitochondria. In turn, this affects the energy conversion process.

The tissues in the body which are most at risk from this small energy deficiency seem to be in the ears and the pancreas, which obviously lead to the symptoms of Deafness and Diabetes.

Each cell has many Mitochondria and each Mitochondrion has many copies of the mtDNA. Some of the mtDNA is correct and some is faulty. The percentage of correct to faulty copies, (Heteroplasmy), determines how old you are before symptoms start and how severe they are.

The percentage of faulty copies of mtDNA (Heteroplasmy), usually varies with age in a consistent pattern. With increased age, it decreases in cells which divide frequently such as skin and blood. However it increases in stable tissues such as muscle, nerves, the brain, ears and pancreas. This explains why symptoms occur later in life and are progressive.

The mtDNA defect, A3243G, is also involved in a number of other diseases, including MELAS, CPEO and others.

See Also
Maternal Inheritance
Heteroplasmy
mtDNA

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