To the Editor: In her Special Communication, Dr Migeon1 reviewed the role of X inactivation and cellular mosaicism in women's health and sex-specific diseases. We believe that there is an important error in Table 2, regarding fragile X syndrome.
Migeon correctly notes that males with fragile X syndrome (full mutation CGG repeat expansion) generally experience moderate to severe mental retardation; however, the phenotype in females with the full mutation was incorrectly listed as “usually normal or mild retardation.” The majority of females with the full mutation are affected cognitively, with 70% demonstrating an IQ in the borderline to mentally retarded range.2 The remaining 30% of females, who have an IQ in the normal range, typically have executive function deficits and often present as learning disabled.2 It is important to recognize the extent of clinical involvement in females to ensure their access to appropriate interventions: special education support and therapy for language, academic, and motor problems; appropriate medication for attention-deficit hyperactivity disorder, anxiety, or mood instability. Such interventions can make a significant difference in school progress and social adjustment.2
Hagerman RJ, Hagerman PJ. X Inactivation and Cellular Mosaicism. JAMA. 2006;296(8):930–931. doi:10.1001/jama.296.8.930-c