Incidence of Fragile X Syndrome by Newborn Screening for Methylated FMR1 DNA

Abstract

Fragile X syndrome (FXS) results from a CGG-repeat expansion that triggers hypermethylation and silencing of the FMR1 gene. FXS is referred to as the most common form of inherited intellectual disability, yet its true incidence has never been measured directly by large population screening. Here, we developed an inexpensive and high-throughput assay to quantitatively assess FMR1 methylation in DNA isolated from the dried blood spots of 36,124 deidentified newborn males. This assay displays 100% specificity and 100% sensitivity for detecting FMR1 methylation, successfully distinguishing normal males from males with full-mutation FXS. Furthermore, the assay can detect excess FMR1 methylation in 82% of females with full mutations, although the methylation did not correlate with intellectual disability. With amelogenin PCR used for detecting the presence of a Y chromosome, this assay can also detect males with Klinefelter syndrome (KS) (47, XXY). We identified 64 males with FMR1 methylation and, after confirmatory testing, found seven to have full-mutation FXS and 57 to have KS. Because the precise incidence of KS is known, we used our observed KS incidence as a sentinel to assess ascertainment quality and showed that our KS incidence of 1 in 633 newborn males was not significantly different from the literature incidence of 1 in 576 (p = 0.79). The seven FXS males revealed an FXS incidence in males of 1 in 5161 (95% confidence interval of 1 in 10,653-1 in 2500), consistent with some earlier indirect estimates. Given the trials now underway for possible FXS treatments, this method could be used in newborn or infant screening as a way of ensuring early interventions for FXS.

Use of State Administrative Data Sources to Study Adolescents and Young Adults with Rare Conditions

“…FXS rates are slightly lower than reported prevalence rates, [38][39][40] whereas SB and MD rates are similar to reported prevalence rates. [41][42][43] The strengths of this method include the diverse types of information available, including data from medical claims, hospital discharges, education, social, and disability services.…”

Fragile X syndrome due to a missense mutation

“…The full mutation leads to transcriptional silencing of FMR1 and is the most common cause of FXS with a prevalence of B1 in 5000 males. 21 Diagnostic testing for FXS is largely limited to full mutation screening. However, a number of conventional mutations have also been demonstrated to lead to FXS.…”

A survey of patients with mental retardation of unknown origin

“…Laboratory diagnosis of FXS by various methods, such as Southern blot, PCR and Karyotype is detected and which in this study two methods, karyotype and PCR were used. Power to detect a suspected diagnosis of FXS karyotype is 99 percent for men and 95 percent for women have been reported (16)(17)(18). Due to high PCR accuracy for diagnosis of FXS, in 7 patients who showed signs of phenotypic Better, PCR analysis was used to identify these individuals.…”

“…Alleles with between 60 and 230 CGG repeats are called permutation. They are generally unmethylated with normal transcript and protein level, but are extremely unstable during transmission to next generation (17). Expansion of premutation into full mutation can only occur by maternal transmission and depends on the length of the maternal pre mutation.…”