Information about a Clinical Trial (0.1Mb) can be downloaded in Adobe Acrobat pdf format.

You can access the trial website at Web: http://lhon.ncl.ac.uk

Leber's Hereditary Optic Neuropathy: Leber's Optic Atrophy: LHON

This is a rare inherited condition which involves the optic nerves with either complete or partial loss of central vision. This disorder is unrelated to Leber's Congenital Amaurosis - the only connection being that they were described by the same doctor.

The optic nerve is the "information cable" joining the eye, the "camera", to the brain. If damage occurs to the retina or the optic nerve then some of the "wires" in the optic nerve will die. The "finest wires" that allow us to see fine detail are lost in LHON. The nerve health can be assessed by looking into the eye. A healthy nerve looks pink and one that has been damaged pale and is called "atrophic". However, early in LHON the nerve can look abnormally pink and slightly swollen. The genetic defect is in the mitochondria, small bodies inside cells that generate their energy.

Normally males lose their eyesight between the ages of fifteen to forty-five, but visual loss may occur in young children or later in life. Often vision is lost in one eye a few months before the other. There may be spontaneous marked improvement in vision several months or even years after abrupt severe vision loss. This observation makes it difficult to assess efficacy of any treatments.

There is loss of central vision and diminished colour vision. Children will have difficulty with reading and fine detail tasks especially with low contrast and small detail work.

Several studies have shown increased risk of vision loss in smokers, in heavy alcohol drinkers and in those with diets deficient in natural antioxidants (substances that inhibit oxidation or reactions promoted by oxygen). The value of vitamin supplementation to a normal diet is not of proven value. There is some evidence of a possible benefit of drugs including steroids and Idebenone in acute disease.

Very rarely individuals have other problems including mild neurological symptoms and cardiac conduction defects with irregularity of heart beat.

Inheritance patterns
This disorder is due to a mutation in the DNA of the mitochondria passed by a mother to her child. LHON may be passed on by mothers who have no symptoms, as females are often mildly affected or unaffected. Males do not pass on LHON to their child.

Genetic testing in one of UK's National reference laboratories, Web: http://www.lwh.nhs.uk/genetics/molecular/services.html is available for adults who may be asymptomatic but who have a close relative with LHON and who wish to know if they are at risk of developing symptoms and their risk of passing on the genetic defect.

Genetic testing is only advised for children with visual loss in whom a diagnosis of LHON is being considered on clinical signs. The mutation (spelling mistake in the DNA) can be detected in about ninety per cent cases thought clinically to have LHON. The majority have one of the following mutations: 11778, 3460, 14484. Whilst symptomatic individuals with 14484 generally have better vision outcome there is much variation even within each group.

Many individuals with these genetic defects, especially females, may have normal vision throughout life. At the moment there is no way of predicting which people carrying a LHON gene will actually go on to lose their eyesight, or how badly their eyesight will be affected.

Prenatal diagnosis
None.

Medical text written October 2004 by Miss Isabelle Russell-Eggitt FRCS FRCOphth, Consultant Ophthalmic Surgeon, Great Ormond Street Hospital for Children, London, UK.

Further Online Resources
Medical texts in The Contact a Family Directory are designed to give a short, clear description of specific conditions and rare disorders. More extensive information on this condition can be found on a range of reliable, validated web sites and links to them are included in the CD-ROM version of this Directory. Further information on these resources can be found in our Medical Information on the Internet article.

There is currently no effective support group covering Leber's Hereditary Optic Neuropathy. This medical description is retained for information purposes. Families can use Contact a Family's Freephone Helpline for advice, information and, where possible, links to other families. Contact a Family's web-based linking service Making Contact.org can be accessed at http://www.makingcontact.org