Newborn screening for fragile X syndrome

Abstract

Fragile X syndrome (FXS), caused by a trinucleotide expansion (>200 CGG repeats) in the fragile X mental retardation gene (FMR1), is currently not included in newborn screening (NBS) panels in the United States as it does not meet the standards for recommendation. Although in the past few years FXS has met many of the criteria for population screening and studies have shown that NBS for FXS is feasible, the idea is still controversial and the debate is open. The recent advances in genomic testing as well as groundbreaking advances in targeted treatment for FXS have been challenging the dogma and principle of the national NBS program: screen only if you can intervene. Arguments in favor of NBS include benefits of early intervention and follow-up for the identified baby, which would justify NBS even in the absence of medical benefit to the child. In addition, the extended family members may benefit from genetic and reproductive counseling, informed decision making before a subsequent pregnancy, and access to treatment and services. However, communicating the results and the potential consequences to families is a challenge and could lead to a heavy psychosocial burden. A controversial issue is the identification of premutation carriers (55-200 CGG repeats), because it not only can lead to information on the reproductive possibility of having a child with FXS but also leads to information about personal health risks associated with the premutation. Yet, knowledge of carrier status could stimulate and encourage lifestyle changes and preventive measures likely to reduce the risk of medical problems reported in premutation carriers. If NBS for FXS is developed, it must be carried out with clear awareness of the potential impact on the lives of the children, and it should be done after counseling and parents' informed consent. Importantly, the infrastructure to support testing, counseling, treatment, and follow-up will have to be made available to the families.

Figure 1

Diagram of the newborn-screening process. From the left, blood collected on a bloodspot card from a heel prick is used to screen newborns for Fragile X. Isolation of DNA, PCR and Capillary Electrophoresis analysis allow measurement of CGG-repeat allele size. The identification of individuals with an FMR1 expanded allele can lead to cascade testing of extended family members. The benefits of cascade testing include early intervention, genetic and reproductive counseling, access to behavioral and pharmacological treatment, and long-term follow-up services.