Newborn screening and prenatal diagnosis for Rett syndrome: implications for therapy.

Most girls with Rett syndrome develop normally prior to the appearance of the typical symptoms. A presymptomatic phase is also observed in many inborn errors of metabolism that are included in newborn screening programs. Diagnostic testing for mutations or large genomic rearrangements involving methyl-CpG binding protein 2 gene (MECP2) is highly sensitive and identifies mutations in up to 95% of female individuals with classic Rett syndrome. This has prompted some to ask whether MECP2 testing should be included in newborn and prenatal screening programs. We review current and evolving practices in these programs, emphasizing their relevance to Rett syndrome. The availability of a reliable test and the characteristic early latent phase, which creates a window of opportunity for early treatment, favor universal newborn screening for Rett syndrome. However, the high cost and the lack of an effective presymptomatic treatment make universal newborn screening for Rett syndrome impractical at present. In contrast, prenatal diagnosis should be offered to the parents of an affected child if the responsible mutation has been identified in the index case.