Simplified strategy for rapid first-line screening of fragile X syndrome: closed-tube triplet-primed PCR and amplicon melt peak analysis.
Premutation and full-mutation hyperexpansion of CGG-triplets in the X-linked Fragile X Mental Retardation 1 (FMR1) gene have been implicated in fragile X-associated tremor/ataxia syndrome, fragile X-associated primary ovarian insufficiency, and fragile X syndrome (FXS), respectively. The currently available molecular diagnostic tests are either costly or labour-intensive, which prohibits their application as a first-line FMR1 test in large-scale population-based screening programs. In this study, we demonstrate the utility of a simplified closed-tube strategy for rapid first-line screening of FXS based on melt peak temperature (Tm) analysis of direct triplet-primed polymerase chain reaction amplicons (dTP-PCR MCA). In addition, we also evaluated the correlation between Tm and CGG-repeat size based on capillary electrophoresis (CE) of dTP-PCR amplicons. The assays were initially tested on 29 FMR1 reference DNA samples, followed by a blinded validation on 107 previously characterised patient DNA samples. The dTP-PCR MCA produced distinct melt profiles of higher Tm for samples carrying an expanded allele. Among the samples tested, we also observed a good correlation between Tm and CGG-repeat size. In the blinded validation study, dTP-PCR MCA accurately classified all normal and expansion carriers, and the FMR1 genotypic classification of all samples was completely concordant with the previously determined genotypes as well as the dTP-PCR CE results. This simple and cost-effective MCA-based assay may be useful as a first-line FXS screening tool that could rapidly screen out the large majority of unaffected individuals, thus minimising the number of samples that need to be analysed by Southern blot analysis.
Department of Pediatrics,Yong Loo Lin School of Medicine,National University of Singapore,Singapore,Singapore.
Indhu-Shree
IS
Rajan-Babu
Department of Pediatric Medicine,KK Women's and Children's Hospital,Singapore,Singapore.
Hai-Yang
HY
Law
Department of Pediatric Medicine,KK Women's and Children's Hospital,Singapore,Singapore.
Chui-Sheun
CS
Yoon
Department of Biochemistry,Yong Loo Lin School of Medicine,National University of Singapore,Singapore,Singapore.
Caroline G
CG
Lee
Department of Pediatrics,Yong Loo Lin School of Medicine,National University of Singapore,Singapore,Singapore.
Samuel S
SS
Chong
D001259:Ataxia / Q000175:diagnosis* / Q000235:genetics*; D051860:Fragile X Messenger Ribonucleoprotein 1 / Q000235:genetics*; D005600:Fragile X Syndrome / Q000175:diagnosis* / Q000235:genetics*; D006801:Humans; D009691:Nucleic Acid Denaturation; D016133:Polymerase Chain Reaction / Q000379:methods*; D013696:Temperature; D014202:Tremor / Q000175:diagnosis* / Q000235:genetics*
D051860:Fragile X Messenger Ribonucleoprotein 1; C497683:FMR1 protein, human