C urrently, researchers don’t know exactly how many people have either the full mutation or the premutation form of the FMR1 gene. Even though researchers can estimate the number of people affected by Fragile X, these estimates can be very different.*
A summary of existing research 5 conducted by the Centers for Disease Control and Prevention in 2001 estimated that approximately one in 3,500 to 8,900 males is affected by the full mutation of the FMR1 gene, and that one in 1,000 males has the premutation form of the FMR1 gene. This study also estimated that one in 250 to 500 females in the general population has the premutation. Another study 6 estimated that one in 4,000 females is affected by the full mutation.
Although these estimates are useful in trying to understand the impact of Fragile X on various communities, keep in mind that these numbers are only the best estimates based on the available information. Many factors can affect the completeness and/or accuracy of the available information, which means that the number of people affected by Fragile X could actually be different. The important thing to remember is that, when you consider the individuals affected by full mutation and premutation forms of the FMR1 gene, their families, and their communities, this condition impacts hundreds of thousands of people.
*The number of people affected by a full mutation or a premutation of the FMR1 gene is still being studied. At the time this booklet was printed, few population-based studies had been done to determine exactly how many people were affected by Fragile X. The estimates included here from Crawford, Acuña, and Sherman differ from other estimates, including those provided by many of the national organizations dedicated to Fragile X (Bailey & Nelson, The Nature and Consequences of Fragile X Syndrome, Mental Retardation and Developmental Disabilities Research Reviews, 1:238-244, 1995; Prevalence of Fragile X Revisited and Revised, The National Fragile X Foundation Quarterly; Winter, 2002). For more information, please consult the specific articles or the national organizations listed in the Where can I go for more information about Fragile X syndrome? section of this booklet.