Monozygotic twin brothers with the fragile X syndrome: different CGG repeats and different mental capacities
A Helderman-van Den Enden… - Journal of medical …, 1999 - jmg.bmj.com
A Helderman-van Den Enden, PD Maaswinkel-Mooij, E Hoogendoorn, R Willemsen…
Journal of medical genetics, 1999•jmg.bmj.comLittle is known about the mechanism of CGG instability and the time frame of instability early
in embryonic development in the fragile X syndrome. Discordant monozygotic twin brothers
with the fragile X syndrome could give us insight into the time frame of the instability. We
describe monochorionic diamniotic twin brothers with the fragile X syndrome who had
different CGG repeats and different mental capacities, whereas the normal mother had a
premutation. The more retarded brother had a full mutation in all his cells and no FMR-1 …
in embryonic development in the fragile X syndrome. Discordant monozygotic twin brothers
with the fragile X syndrome could give us insight into the time frame of the instability. We
describe monochorionic diamniotic twin brothers with the fragile X syndrome who had
different CGG repeats and different mental capacities, whereas the normal mother had a
premutation. The more retarded brother had a full mutation in all his cells and no FMR-1 …
Little is known about the mechanism of CGG instability and the time frame of instability early in embryonic development in the fragile X syndrome. Discordant monozygotic twin brothers with the fragile X syndrome could give us insight into the time frame of the instability.
We describe monochorionic diamniotic twin brothers with the fragile X syndrome who had different CGG repeats and different mental capacities, whereas the normal mother had a premutation. The more retarded brother had a full mutation in all his cells and no FMR-1 protein expression in lymphocytes, whereas the less retarded brother had 50%/50% mosaicism for a premutation and full mutation and FMR-1 protein expression in 26% of his lymphocytes.
The differences in repeat size could have arisen either before or after the time of splitting. The time of splitting in this type of twin is around day 6-7. Given the high percentage of mosaicism, we hypothesise that the instability started before the time of splitting at day 6-7.
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