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Early development in fragile x syndrome Implications for developmental screening

Fragile X syndrome (FXS), the most common inherited form of intellectual disability, is not obvious at birth. The average age of diagnosis is around 36 months, a figure that has remained unchanged over the past decade. A primary challenge has been the lack of a definitive profile of early development in FXS. This chapter reviews the research that has been conducted relevant to this question. Research has been severely hampered by the fact that in the absence of population screening of newborns, it is virtually impossible to identify a sufficient and representative sample of infants to study. The research that has been conducted suggests that critical neurobiological processes are almost certainly affected in utero and in the early months of development. Consequently, many but not all males with FXS show delays during the latter part of the first year of life. This statement would be less true for females and for premutation carriers. We predict that a best case scenario for promoting earlier identification would be through regular developmental screening of infants in pediatric practice and rapid referral for genetic testing of any infant with developmental delays. Even if these policies could be implemented effectively, however, diagnosis of FXS would, at best, occur at an average age of 16–18 months. More research on early development is needed to further enhance understanding of clinical symptoms during the first year of life, but thus far it appears that a signature FXS profile will be difficult to identify. Population screening, such as newborn screening, will be the only realistic approach to identifying all children with FMR1 gene mutations.


Bailey, D., Hazlett, HC., Roberts, JE., & Wheeler, A. (2011). Early development in fragile x syndrome: Implications for developmental screening. In DJ. Fidler (Ed.), International Review of Research in Developmental Disabilities: Early Development in Neurogenetic Disorders (pp. 75-108). San Diego, CA: Elsevier. https://doi.org/10.1016/B978-0-12-374478-4.00004-6