Complex neurologic syndrome associated with the G1606A mutation of mitochondrial DNA.
OBJECTIVE
To confirm the pathogenicity of the G-to-A substitution at nucleotide 1606 (G1606A) mutation in the mitochondrial DNA (mtDNA) tRNA(Val) gene, and to characterize genotype-phenotype correlation.


METHODS
A 37-year-old man since childhood developed a complex clinical picture characterized by hearing loss, migraine, ataxia, seizures, cataracts, retinitis pigmentosa, mental deterioration, and hypothyroidism. Magnetic resonance imaging revealed diffuse calcification of the basal ganglia and cerebral cortical atrophy. Morphologic and biochemical studies of respiratory chain complexes were performed in skeletal muscle. All 22 mitochondrial tRNA genes were screened for mutations by direct sequencing.


RESULTS
Biochemical analysis showed normal activities of respiratory chain enzymes and citrate synthase; morphologic examination showed scattered ragged-red fibers and poor or absent cytochrome c oxidase staining in 10% of the fibers. A heteroplasmic G1606A transition in the mtDNA tRNA(Val) gene was found. Mutant DNA was 70% of the total in the proband's muscle. The mutation was absent in blood samples and urinary sediment from his healthy brother and mother.


CONCLUSIONS
This second patient with the G1606A mutation confirms both the pathogenicity of the mutation and its association with a characteristic complex neurologic phenotype.
Sacconi
Sabrina
S
Department of Neurology, Columbia University, New York, NY, USA.
Salviati
Leonardo
L
Gooch
Clifton
C
Bonilla
Eduardo
E
Shanske
Sara
S
DiMauro
Salvatore
S
D000225:Adenine; D000328:Adult; D001921:Brain / Q000201:enzymology / Q000473:pathology; D004272:DNA, Mitochondrial / Q000235:genetics* / Q000378:metabolism; D006147:Guanine; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000201:enzymology; D009154:Mutation / Q000235:genetics*; D009422:Nervous System Diseases / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D012343:RNA, Transfer / Q000235:genetics; D013577:Syndrome
D004272:DNA, Mitochondrial; D006147:Guanine; D012343:RNA, Transfer; D000225:Adenine