External Ophthalmoplegia, POLG and mtDNA Mutations

Clinical Characteristics
Ocular Features: 

Progressive external ophthalmoplegia of these types is often associated with widespread neurological and muscle manifestations.  The ophthalmoplegia is adult in onset and frequently combined with exercise intolerance.  Significant lens opacities may be seen in early childhood but may not cause vision problems until early adulthood. Progressive ptosis is often an early and disabling sign.

Systemic Features: 

Facial muscles can be weak, generally in older individuals.  Some patients complain of dysphagia.  Sensoirneural hearing loss, dysarthria, and dysphonia are often associated.  Neurological symptoms include ataxia, sensory neuropathy, tremors, depression and symptoms of parkinsonism but these are variable.   Some patients experience rhabdomyolysis following alcohol consumption.  Dilated cardiomyopathy can be a part of the autosomal recessive form of this disease.

A possible subcategory of this disease is associated with hypogonadism evidenced by delayed sexual maturation, primary amenorrhea, early menopause and testicular atrophy.  Other features as described above may be associated.  Muscle biopsy shows ragged-red fibers with multiple mitochondrial deletions.

Genetics

Progressive external ophthalmoplegia of the type described here is the result of mutations in the autosomal gene POLG combined with deletions in mitochondrial DNA.  POLG mutations account for 13-45% of patients with progressive external ophthalmoplegia who also have mitochondrial deletions.  The inheritance pattern in some families resembles the classical autosomal dominant pattern (PEOA1, 157640) whereas in others the pattern suggests autosomal recessive transmission (PEOB, 258450).  The autosomal defect is in the POLG gene at locus 15q25 which codes for the nuclear-encoded DNA polymerase-gamma gene.  The phenotype in the recessive disease tends to be more severe than in autosomal dominant cases. 

Other autosomal mutations with a less complex clinical picture associated with ophthalmoplegia are located in genes ANT1 (SLC25A4) (609283) at 4q35, and C10ORF2 (606075) at 10q24.

Treatment
Treatment Options: 

No effective treatment is available for the general disorder but consideration should be given to ptosis repair.

References
Article Title: 

References

Hirano M, DiMauro S. ANT1, Twinkle, POLG, and TP: new genes open our eyes to ophthalmoplegia. Neurology. 2001 Dec 26;57(12):2163-5.

PubMedID: 11756592

Filosto M, Mancuso M, Nishigaki Y, Pancrudo J, Harati Y, Gooch C, Mankodi A, Bayne L, Bonilla E, Shanske S, Hirano M, DiMauro S. Clinical and genetic heterogeneity in progressive external ophthalmoplegia due to mutations in polymerase gamma. Arch Neurol. 2003 Sep;60(9):1279-84.

PubMedID: 12975295

Lamantea E, Tiranti V, Bordoni A, Toscano A, Bono F, Servidei S, Papadimitriou A, Spelbrink H, Silvestri L, Casari G, Comi GP, Zeviani M. Mutations of mitochondrial DNA polymerase gammaA are a frequent cause of autosomal dominant or recessive progressive external ophthalmoplegia. Ann Neurol. 2002 Aug;52(2):211-9.

PubMedID: 12210792