Methylation analysis in newborn screening for fragile X syndrome.

Methylation Analysis in Newborn Screening for Fragile X Syndrome To the Editor In a recent issue of JAMA Neurology, Tassone1 presented arguments for and against newborn screening (NBS) for fragile X syndrome (FXS), which is caused by large CGG expansion mutations (FM) in the gene FMR1. Tassone described the drawbacks of detecting the smaller gray-zone (GZ) and premutation (PM) alleles, which do not cause FXS but are nonetheless detected by assays based on CGG-expansion sizing. A contentious ethical issue is the detection of the late-onset conditions, fragile X–associated tremor/ataxia syndrome and fragile X–associated primary ovarian insufficiency, in infant carriers of PM alleles and the incomplete understanding of the clinical significance of GZ and PM alleles in child development. The justification for including GZ alleles in the screen is debatable because follow-up cascade testing of relatives of GZ allele carriers would yield very few carriers of PM or FM alleles. Furthermore, because the reported prevalence1 of GZ in the general population is approximately 1 in 26, from a funding and infrastructure perspective, the task of providing pretest counselling and posttest follow-up would be monumental if not impossible. We propose an alternative screening protocol, where FMR1 methylation analysis would be used as the first-line test to selectively identify only FM carriers, followed by a tripleprimed CGG-based test to confirm the positive results. This would ensure that the benefits of NBS are focused on FXS, where the genetic pathology is well understood and the ethical and counseling problems1 are avoided. In 2009, Coffee et al2 demonstrated the feasibility of screening using FMR1 CpG island methylation testing in 36 124 NBS spots and provided prevalence of FM as 1 in 5161 in the US male general population. This is a similar prevalence estimate to that reported using CGG sizing.1 More recently, we described several assays targeting methylation of FMR1 intron 1 biomarkers3,4; these can be used to detect the FXS-causing methylated FM alleles in NBS spots of boys and girls while excluding between 97% and 100% of the smaller PM expansions and 100% of the GZ expansions.3-5 This approach offers the possibility of providing a costeffective screen for FXS, a disorder that is comparable in terms of prevalence and family health burden to cystic fibrosis, which is included widely in NBS programs.