LHON

How LHON is passed on

A LHON Gene passing through a family tree

Family Tree


This family tree shows how a LHON gene can be passed on from generation to generation.


At the top of the tree, in Generation 1, there is one couple. The woman in the couple is carrying a LHON gene. She may not show any symptoms herself.

The couple have three children, who are in Generation 2. All three of the children will carry the LHON gene, although they may not lose their eyesight. The first child is a girl who has no further children. The second child is a boy, who does have children, and the third child is another girl, who has children.

The grandchildren in this family form Generation 3. The first two grandchildren had a father carrying the LHON gene, and will not have inherited it from him. The other two grandchildren had a mother carrying the LHON gene, and will both have inherited the LHON gene from her.

In Generation 1

 There is a couple, a man not carrying the LHON gene and a woman who is carrying the LHON gene.

In Generation 2

 All of the children of the woman carrying the LHON gene now also carry the LHON gene.

In Generation 3

 The children of the man in Generation 2 cannot carry the LHON gene as men do not pass on the gene.

The children of the woman in Generation 2 do carry the LHON gene.

LHON is inherited only from the mother.
A man CANNOT pass on a LHON gene to his children.


Important note

Carrying a LHON gene does NOT mean someone will definitely lose their eyesight. Many people in a family can carry a LHON gene without ever losing sight due to LHON. We do not yet know what extra factor triggers loss of sight.


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This page last updated 03 August 1997 Copyright © Jim Leeder 1997