Estimated to affect more than 400 million people around the world, diabetes is one of the most common chronic disorders, with a range of different types – including a mitochondrial disease that manifests as diabetes. Maternally inherited diabetes and deafness, or MIDD, was identified as a specific condition in the early 1990s, after a team of scientists examined reports suggesting an increased incidence of some forms of diabetes being transmitted from mother to child.  

Like classic MELAS syndrome, most cases of MIDD are caused by the much studied 3243A>G mutation in our mitochondrial DNA.

It was the increased incidence of diabetes being transmitted from mother to child, which suggested that the disorder could be linked to our mitochondria. This is because the mitochondria we inherit are only from our mothers, so this genetic mutation is passed down from an affected mother to all her children.

According to literature, at least 0.1 percent of people with diabetes have MIDD, although there is variation in how those inheriting the mitochondrial mutation are affected. MIDD symptoms tend to develop in mid-adulthood, although the age they occur can vary from childhood to late adulthood.

Diagnosis of MIDD is difficult and can often go unrecognised or be misdiagnosed as the much more common Type 1 or Type 2 diabetes. Most people with MIDD who have symptoms of diabetes can initially be treated with dietary changes or medication, although insulin therapy is usually needed eventually.

Typically, sensorineural hearing loss occurs before diabetic symptoms, is more common in men than women and can be more severe and rapidly progressive. It tends to begin with patients being unable to hear higher frequencies and this progressively declines over the years to complete hearing loss.

Early detection of deafness in children is important to manage MIDD effectively and physicians will usually monitor for ear infections closely. Cochlear implants can prove effective in cases of severe hearing loss in MIDD and, as hearing loss progresses, hearing aids will often be used.

As well as classic symptoms of diabetes and hearing loss, MIDD can also exhibit clinical symptoms of MELAS, given both are characterised by the same 324A>G mutation in our mitochondrial DNA. These can include cognitive decline, with studies reporting poorer performances in sustained attention, verbal memory working and abstract reasoning, among MIDD patients compared to those with Type 1 diabetes.

The significance of cognitive decline in mitochondrial disease and the serious effect it can have on normal daily living means it is a key focus of our research at Khondrion. That’s why current trials of our investigational medicine, in development to treat a range of mitochondrial diseases,  are examining its impact on cognitive functioning.