Screening for Fragile X Syndrome (Murray et al.) - NIHR Journals ...

Health Technology Assessment 1997; Vol. 1: No. 4List of abbreviations and glossaryTechnical terms and abbreviations are used throughout this report. The meaning is usually clear fromthe context but a glossary is provided for the non-specialist reader. In some cases usage differs in theliterature but the term has a constant meaning throughout this review.AGG (adenine–guanine–guanine)Trinucleotide usually interspersed in theCGG repeat sequence in the FMR-1 gene.Carrier Individual with an FM or PM.Cascade screening Testing members of aproband’s family.Case-finding Actively trying to diagnoseprobands for cascade screening.CGG (cytosine–guanine–guanine)Trinucleotide repeated in the FMR-1 gene.CVS (chorionic villus sampling) Invasiveprocedure to obtain placental tissue forprenatal diagnosis.Detection rate Proportion of affectedindividuals with positive results.Expansion Increase in the repeat sequencebetween generations.False-positive rate Proportion of unaffectedindividuals with positive results.FM (full mutation) Array of repeat sizeover 200.FMR (fragile X mental retardation) FragileX syndrome.FMR-1 Gene which is mutated in fragileX syndrome.FMRP Protein product normally transcribedby FMR-1.FRAXA Fragile site associated with fragileX syndrome.FRAXE Fragile site on the X chromosomewhich is associated with mildmental handicap.FRAXD & F Fragile sites close to FRAXA & E.Haplotype Combination of linkedgenetic markers.LCR Ligase chain reaction.Mosaicism Individual with more than one cellline of different genetic composition.nCGG A sequence of n repeats.Negative predictive value Probability that anindividual with a negative result is unaffected.NTM (normal transmitting male) Unaffectedmale with a PM.Obligate carrier Person who from pedigreeanalysis must have passed on an affected gene.PCR (polymerase chain reaction) Method ofamplifying small amounts of DNA.PM (pre-mutation) Array of repeat size 53 or55–200.Positive predictive value Probability that anindividual with a positive result is affected.Proband Affected individual through whomattention is drawn to a pedigree.PUBS (peripheral umbilical cord bloodsampling) Invasive procedure to obtain foetalblood for prenatal diagnosis.Pure repeat size The largest contiguousnumber of CGG repeats in an array withoutintervening AGGs.RED Repeat expansion detection.Repeat sequence Section of DNA containingthe CGG repeats.Repeat size Total number of repeats in anarray, both CGG and AGG.Triplet Trinucleotide.Xq27.2 Locus of FRAXD.Xq27.3 Locus of FRAXA.Xq28 Locus of FRAXE & F.i