Peter Kay: Comic’s ‘first-hand experience’ of ‘complex’ disease – condition explained

Mitochondrial DNA depletion syndrome (MDDS) is another syndrome caused by mitochondrial DNA problems. MDDS are associated with many clinical features, some of which can be fatal in childhood. The type and severity of symptoms will often depend on the particular gene that is affected.

In some cases, the main feature is progressive muscle weakness, which can make it difficult to breathe and lead to respiratory failure. Other causes affect the brain, with seizures, stroke-like episodes, movement disorders, or developmental delay common.

A third syndrome, Leigh syndrome (also known as Leigh disease), is a mitochondrial disorder that typically affects young children. As a serious condition, it usually causes difficulty with movement, posture, and mental ability.

It is important to note that Leigh syndrome is caused by a number of different genetic errors (mutations) found in nuclear or mitochondrial DNA and therefore can be inherited in different ways.