Mitochondrial ND3 As The Novel Causative Gene For Leber Hereditary Optic Neuropathy And Dystonia

Leber hereditary optic neuropathy and dystonia (LDYT) characterized by maternal hereditary optic neuropathy variably associated with dystonia and other systemic disorders has been recognized as a unique oxidative phosphorylation disorder caused by mutations in mitochondrial ND6, ND4 or ND1 gene. A Chinese Han family lived in Anhui province with 18 patients and 46 family members was investigated. The patients developed visual loss and optic atrophy from teenage to the third decades, variably associated with generalized dystonia with onset in childhood and prominent symmetric lucencies in the basal ganglia revealed by CT and MRI. Blue-green achromat, pyramidal signs and other central nerve system disorders were found in certain family members. Histochemistry stain of biopsied muscles from two patients with generalized dystonia did not show evidence of abnormal oxidative phosphorylation. Electrical microscopy did not reveal prominent changes on amount or construction of mitochondrion. After analyzed the high frequency mutations of LHON named as 'primary mutation' and ntl4459A which is a well-known LDYT causative mutation, the nucleotide sequences of the entire mitochondrial genomes in four selected family members (one LHON, one LDYT, one asymptomatic maternal relative and one asymptomatic paternal relative) were determined by employing a DNA microarray designed for mitochondrial DNA (Affymetrix^TM). The base changes identified by the microarray were further confirmed by conventional direct nucleotide sequence analysis. The mutant loading was analyzed by SSCP and RFLP based on genetic analysis system. There are 51 mitochondrial DNA variants were identified in the entire mitochondrial DNA among the four family members. But 50 variants are synonymous polymorphisms referring to rCRS (Human mtDNA Revised Cambridge Reference Sequence). Only one nonsynonymous mutation (G10197A) substituting a hydroxymethyl-sided threonine for a highly conserved hydrophobic alanine at the codon 47 of mtND3 on the background of mitochondrial haplogroup D4b was identified in the mitochondrial DNA of all the affected members and two asymptomatic maternal relatives, while it was not present in paternal relatives or 101 normal individuals with same genetic background or 70 patients with mitochondriopathies including two siblings with LDYT phenotype. SSCP and RFLP demonstrated the mutant loading in all maternal relatives was 100%, which means it is a homoplasmic mutation at the site of nt10197. Although absent direct evidence of respiratory chain defect in the family until now, there are several lines of evidence to supporting the pathological role of nt10197A mutation. Although several mutations around MT10197 involving ND3 gene have been reported as the causes of Leigh syndrome or Leigh-like encephalopathy, this is the first description of the ND3 mutation causing LDYT. The reported The variable phenotype on the background of same mitochondrial mutation suggests that mitochondrial haplogroup and nuclear factors affect the onset of LDYT.