How Common Are Mitochondrial Diseases?

How Common Are Mitochondrial Diseases?

It is natural when hearing the term ‘mitochondrial disease’ ,for the first time, to assume that the reason you’ve not heard of it before ,is because it is a rare illness. In fact, recent research is suggesting that the condition, or, more accurately, the conditions, are ,at least ,as common as other better known neuro-muscular disorders and disabling conditions. But, whereas many other neurological and muscular conditions have been known for over a century, mitochondrial disorders have only been recognised from the later decades of the 20th century. So, quite simply, we are still only just finding out about them.

The mitochondria perform a crucial role in energy production. This is carried out by about 70 proteins within the mitochondrion. A mitochondrion has its own DNA. (mtDNA) but most of these proteins are synthesised from ‘codes’ in the DNA contained in the main cell nucleus. Only 13 of them are coded by the DNA present in the mitochondrion itself (mtDNA). The genetic fault underlying a mitochondrial disorder can be caused either by defective genes in the main cell nucleus or by a defect in the mitochondrial DNA.

Professor D Turnbull ,Dr P Chinnery and colleagues of Newcastle University recently conducted a study in the North East of England, on the occurrence of diseases caused by defective mtDNA . They discovered that about 12 out of every 100,000 either had an illness caused by defective mtDNA or were at risk of developing such an illness.

In an article in ‘Mitochondrial News’, the journal of the United Mitochondrial Disease Foundation (fall/winter edition 2001)*, Professor Turnbull and Dr Chinnery also point to two recent studies of childhood manifestations. A study in Victoria , Australia , by Professor Thorburn and others established an occurrence of about 5 mitochondrial disease cases per 100,000 births. A similar study in western Sweden by Professor Darin and colleagues arrived at the same frequency. In both these studies, which were exclusively of children, it was found that in the majority of cases the underlying genetic defect was in the nuclear DNA not the mitochondrial DNA

Combining the results of these three studies, i.e disease caused by nuclear DNA defects and mtDNA defects , Professor Turnbull and Dr Chinnery have pointed to a mitochondrial disease frequency of 1 in 9000 meaning that between 6000 and 7000 people in the United Kingdom will develop a mitochondrial disorder at some point in their lives.

It must be stressed that this prediction is based on what is understood as proven mitochondrial cases given the present state of knowledge of these conditions. As understanding and diagnostic techniques improve the likelihood is that this is a underestimation . Mitochondrial conditions are not rare diseases.

*How Common are Mitochondrial Disorders ? D.Turnbull: P Chinnery
Fall/Winter 2001 edition of Mitochondrial News ( United Mitochondrial Disease Foundation)