Clinical and genetic heterogeneity in progressive external ophthalmoplegia due to mutations in polymerase gamma.
BACKGROUND
The mendelian forms of progressive external ophthalmoplegia (PEO) associated with multiple mitochondrial DNA deletions are clinically heterogeneous disorders transmitted as dominant or recessive traits. Autosomal dominant PEO is caused by mutations in at least 3 genes: adenine nucleotide translocator-1 (ANT1), encoding the muscle-specific adenine nucleotide translocator; chromosome 10 open reading frame 2 (C10orf2), encoding Twinkle helicase; and polymerase gamma (POLG), encoding the alpha subunit of polymerase gamma. Mutations in POLG can also cause autosomal recessive PEO, which is often associated with multisystemic disorders.


OBJECTIVE
To further investigate the frequency and genotype-phenotype correlations of mutations in the POLG gene, we used single-stranded conformational polymorphism analysis and direct sequencing to screen 30 patients with familial or sporadic PEO and multiple mitochondrial DNA deletions in muscle but without mutations in ANT1 and C10orf2.


RESULTS
Four unrelated patients had novel POLG mutations. A woman with PEO and mental retardation had a heterozygous Gly1076Val mutation. Two patients, one with PEO, exercise intolerance, and gastrointestinal dysmotility and the other with PEO, neuropathy, deafness, and hypogonadism, both had a Pro587Leu change. The fourth patient, who was compound heterozygous for Ala889Thr and Arg579Trp mutations, had PEO, gastrointestinal dysmotility, and neuropathy. These mutations were not detected in 120 healthy control alleles.


CONCLUSIONS
Our results demonstrate that POLG mutations account for a substantial proportion of patients (13%) with PEO and multiple mitochondrial DNA deletions and cause both clinically and genetically heterogeneous disorders.
Filosto
Massimiliano
M
Department of Neurology, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA.
Mancuso
Michelangelo
M
Nishigaki
Yutaka
Y
Pancrudo
Jacklyn
J
Harati
Yadollah
Y
Gooch
Clifton
C
Mankodi
Ami
A
Bayne
Lydia
L
Bonilla
Eduardo
E
Shanske
Sara
S
Hirano
Michio
M
DiMauro
Salvatore
S
D000328:Adult; D002874:Chromosome Mapping; D002879:Chromosomes, Human, Pair 10 / Q000235:genetics; D004265:DNA Helicases; D004252:DNA Mutational Analysis; D000074002:DNA Polymerase gamma; D019915:DNA Primase / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D004259:DNA-Directed DNA Polymerase / Q000235:genetics*; D018450:Disease Progression; D005260:Female; D018740:Genetic Heterogeneity; D008040:Genetic Linkage; D005838:Genotype; D006801:Humans; D008297:Male; D008875:Middle Aged; D024101:Mitochondrial Proteins; D009886:Ophthalmoplegia / Q000235:genetics*; D010375:Pedigree; D010641:Phenotype; D017354:Point Mutation / Q000235:genetics*; D012150:Polymorphism, Restriction Fragment Length; D012097:Repressor Proteins / Q000235:genetics; D014764:Viral Proteins / Q000235:genetics
C081160:Ant protein, Enterobacteria phage P22; D017931:DNA Primers; D024101:Mitochondrial Proteins; D012097:Repressor Proteins; D014764:Viral Proteins; D019915:DNA Primase; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase; C413027:POLG protein, human; D004265:DNA Helicases; C431576:TWNK protein, human