Reverse mutations in the fragile X syndrome.
Three females were identified who have apparent reversal of fragile X premutations. Based on haplotype analysis of nearby markers, they were found to have inherited a fragile X chromosome from their premutation carrier mothers, and yet had normal size FMR1 repeat alleles. The changes in repeat sizes from mother to daughter was 95 to 35 in the first, 145 to 43 in the second, and 82 to 33 in the third. In the first family, mutations of the nearby microsatellites FRAXAC2 and DXS548 were also observed. In the other two, only mutations involving the FMR1 repeats were found. We suggest differing mutational mechanisms such as gene conversion versus DNA replication slippage may underlie such reversions. We estimate that such revertants may occur among 1% or less of premutation carrier offspring. Our results indicate that women identified to be carriers by linkage should be retested by direct DNA analysis.
Brown
W T
WT
New York State Institute for Basic Research in Developmental Disabilities, Staten Island, New York 10314, USA.
Houck
G E
GE
Ding
X
X
Zhong
N
N
Nolin
S
S
Glicksman
A
A
Dobkin
C
C
Jenkins
E C
EC
D004261:DNA Replication; D005260:Female; D051860:Fragile X Messenger Ribonucleoprotein 1; D005600:Fragile X Syndrome / Q000235:genetics*; D005785:Gene Conversion; D006580:Genetic Carrier Screening; D008040:Genetic Linkage; D005819:Genetic Markers; D006239:Haplotypes; D006801:Humans; D008297:Male; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics*; D009679:Nuclear Family; D010375:Pedigree; D016601:RNA-Binding Proteins; D018911:Trinucleotide Repeats
D051860:Fragile X Messenger Ribonucleoprotein 1; D005819:Genetic Markers; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; C497683:FMR1 protein, human