Expansion and methylation status at FRAXE can be detected on EcoRI blots used for FRAXA diagnosis: analysis of four FRAXE families with mild mental retardation in males.
The original test for the analysis of the CCG expansion at the FRAXE locus involves Southern blot analysis of HindIII digests. We show that, by using a different probe, the FRAXE mutation can be detected easily on the same EcoRI or EagI+EcoRI blots as are used for detection of FRAXA. Unexpectedly, we found that both the expansion and methylation status can be determined on a single EcoRI digest, because of the presence of a methylation-sensitive EcoRI site very close to the CCG repeat. We thus detected in a series of mentally retarded individuals previously tested for FRAXA expansion a FRAXE proband who led to the identification of a large sibship (7 of 10 children carrying a mutation). We also show that two fragile X families without FRAXA mutation that previously have been described by Oberlé et al. have the FRAXE expansion. In another family also ascertained initially by cytogenetic finding of a fragile X site, we performed the combined cytogenetic and molecular prenatal diagnosis of a mutated male fetus. All nine males (>3 years old) in whom we found a methylated mutation had mild mental retardation. Our results suggest that the threshold of repeat length for abnormal methylation and fragile-site expression may be smaller at FRAXE than at FRAXA.
Biancalana
V
V
Service de Diagnostic Génétique, Institut de Chimie Biologique, Strasbourg, France.
Taine
L
L
Bouix
J C
JC
Finck
S
S
Chauvin
A
A
De Verneuil
H
H
Knight
S J
SJ
Stoll
C
C
Lacombe
D
D
Mandel
J L
JL
D000293:Adolescent; D000328:Adult; D015139:Blotting, Southern; D002648:Child; D002675:Child, Preschool; D043283:Chromosome Fragile Sites; D002873:Chromosome Fragility; D015246:Deoxyribonuclease EcoRI / Q000378:metabolism; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D005260:Female; D051860:Fragile X Messenger Ribonucleoprotein 1; D005600:Fragile X Syndrome / Q000235:genetics*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008607:Intellectual Disability / Q000235:genetics*; D008297:Male; D009419:Nerve Tissue Proteins / Q000235:genetics*; D009687:Nuclear Proteins; D010375:Pedigree; D011506:Proteins / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics*; D015534:Trans-Activators
D015246:Deoxyribonuclease EcoRI; D015252:Deoxyribonucleases, Type II Site-Specific; D051860:Fragile X Messenger Ribonucleoprotein 1; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D011506:Proteins; D016601:RNA-Binding Proteins; D015534:Trans-Activators; C099930:AFF2 protein, human; C497683:FMR1 protein, human; C046751:endodeoxyribonuclease XmaIII