Pre-excitation syndrome is common in families with Leber's hereditary optic 
neuropathy (LHON). 24 Finnish families with LHON were screened for the 11778 and 
the 3460 mitochondrial DNA mutations. 5 of 30 individuals with LHON and the 
11778 mutation had the Wolff-Parkinson-White pre-excitation syndrome. None of 10 
with the 3460 mutation or of 11 with "other" mutations had this syndrome. 
Overall, 5 of 51 LHON patients and 9 of 112 symptom-free maternal relatives had 
Wolff-Parkinson-White syndrome (9%). In paternal relatives, the frequency was 
1.6%. Mitochondrial DNA causal for LHON may contribute to pre-excitation 
syndrome.