Monozygotic twin brothers with the fragile X syndrome: different CGG repeats and different mental capacities

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...

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Bibliographic Details
Published in:Journal of medical genetics 1999-03, Vol.36 (3), p.253-257
Main Authors: Helderman-van den Enden, A T J M, Maaswinkel-Mooij, P D, Hoogendoorn, E, Willemsen, R, Maat-Kievit, J A, Losekoot, M, Oostra, B A
Format: Article
Language:English
Subjects:
Biological and medical sciences
CGG repeat
Child, Preschool
Chromosome fragility (bloom syndrome, ataxia telangiectasia, fanconi anemia, x-linked mental retardation...)
DNA Methylation
Female
Fragile X Mental Retardation Protein
fragile X syndrome
Fragile X Syndrome - genetics
Fragile X Syndrome - metabolism
Fragile X Syndrome - psychology
Humans
Intellectual disabilities
Lymphocytes
Male
Males
Medical genetics
Medical sciences
mental retardation
monozygotic twins
Mutagenesis
Mutation
Nerve Tissue Proteins - genetics
Nerve Tissue Proteins - metabolism
Pedigree
RNA-Binding Proteins
Short Report
Trinucleotide Repeats
Twins
Twins, Monozygotic - genetics
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Summary: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.
ISSN:0022-2593
1468-6244
DOI:10.1136/jmg.36.3.253