Alpers’ syndrome is a mitochondrial disease that is part of a larger group of conditions collectively known as mitochondrial DNA depletion disorders. It is most often caused by mistakes in the DNA of a gene called POLG (pronounced “pawl-gee”) and is part of a spectrum of POLG-related diseases.
Large-scale mitochondrial DNA deletions
The term single deletion describes a piece of DNA that is missing from lots of copies of mitochondrial DNA in each cell. This is usually not an inherited condition, but one that occurs by chance (sporadic). The rare families with more than one affected member almost always have additional more complex DNA features.
Leigh syndrome (also known as Leigh disease) is a mitochondrial disease that usually affects young children. It is a severe neurological condition that typically affects development of movement, posture and mental abilities, with children sometimes losing these skills after a period of what appeared to be normal development.
Mitochondrial DNA depletion syndrome (MDDS)
It is important that mitochondrial DNA (mtDNA) is correctly maintained to allow the mitochondria to function. Problems with mtDNA maintenance can reduce the amount and quality of the mtDNA, which can lead to impaired energy production. This can cause a particular type of mitochondrial disease known as mitochondrial DNA depletion syndrome (MDDS).
Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis and Stroke-Like Episodes (MELAS) 3243 A>G mutation
This is one of the most common causes of mitochondrial disease. Patients with this mutation have variable disease manifestations ranging from no symptoms at all, to being quite severely affected with the syndrome called MELAS , this is the short name for a collection of symptoms calledmitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes.
Mitochondrial Neuro-gastro-intestinal encephalopathy (MNGIE)
This is a rare mitochondrial condition which is due not to a defect in mitochondrial DNA but due to a defect in an enzyme called thymidine phosphorylase. As this is not inherited through the mitochondrial DNA, the disease only occurs if both parents carry a faulty gene, giving the patient two faulty copies of the thymidine phosphorylase gene.
Multiple mitochondrial DNA deletions
“Multiple mitochondrial DNA Deletions” refers to the different sized pieces of mitochondrial DNA that are missing. The genetic problem here is often inherited, but is not due to a mutation in mitochondrial DNA. The defect can occur in one of a number of nuclear genes that control the maintenance, repair or supply of building blocks for mitochondrial DNA.
Myoclonic Epilsepy and Ragged Red Fibres (MERRF 8344 A>G)
This is also a common mutation causing mitochondrial disease. When present it frequently runs in families with families showing a pattern of maternal inheritance. In patients with this particular mitochondrial DNA mutation there are very variable clinical features.
Neurogenic weakness, Ataxia, and Retinitis Pigmentosa (NARP)
This syndrome describes a group of patients who have a combination of features including weakness, unsteadiness of movement, impaired sensation (neuropathy) and visual disturbance. The weakness is usually found in the muscles around the large joints such as the hip and shoulder, rather than the hands or feet (proximal myopathy).