Human Molecular Genetics, Vol 6, 1063-1068, Copyright © 1997 by Oxford University Press
Y Takiyama, K Sakoe, M Soutome, M Namekawa, T Ogawa, I Nakano, S Igarashi, M Oyake, H Tanaka, S Tsuji and M Nishizawa
To investigate the mechanism of the meiotic instability of expanded CAG
repeats in the gene for Machado-Joseph disease (MJD1), we analyzed the CAG
repeat sizes of 1036 single sperm from six individuals with Machado- Joseph
disease (MJD). The segregation ratio between single sperm with an expanded
allele and those with a normal allele is significantly different (P
<0.0001) from the expected 1:1 segregation ratio, which demonstrates
segregation distortion of expanded alleles in male meiosis. In single sperm
from individuals with the [expanded (CAG)n- CGG]/[normal (CAG)n-GGG]
genotype, significantly greater instability of the CAG repeat was observed
compared with single sperm from individuals with the [expanded
(CAG)n-CGG]/[normal (CAG)n-CGG] genotype (F-test, P <0.001). These
findings in single sperm confirm non-Mendelian transmission of the MJD1
gene and the effect of the intragenic CGG/GGG polymorphism on the
intergenerational instability of the CAG repeats in the MJD1 gene, which
have been observed in clinical and genetic studies. Our results indicate
similarities and dissimilarities between MJD and Huntington's disease or
myotonic dystrophy in terms of the inter-allelic interaction, segregation
distortions and size distribution of trinucleotide repeats in mutant
alleles. Further study is required to determine whether there is a common
mechanism underlying the instability of the triplet repeats in 'triplet
repeat diseases'.
ARTICLES
Single sperm analysis of the CAG repeats in the gene for Machado-Joseph disease (MJD1): evidence for non-Mendelian transmission of the MJD1 gene and for the effect of the intragenic CGG/GGG polymorphism on the intergenerational instability
Department of Neurology, Jichi Medical School, Minamikawachi, Tochigi, Japan.
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