Brief report Cancer incidence among persons with fragile X syndrome in Finland: a population-based study R. Sund, 1 E. Pukkala 2 & K. Patja 3 1 National Research and Development Centre forWelfare and Health (STAKES), Helsinki, Finland 2 Finnish Cancer Registry, Helsinki, Finland; University of Tampere,Tampere, Finland 3 National Public Health Institute, Helsinki, Finland Abstract Background Fragile X syndrome is a common inheritable cause of intellectual disability (ID) and is characterised by a large number of CGG repeats at the gene FMR located on the X-chromosome. It has been reported that this genetic mechanism may protect against malignant transformations. Methods We extracted from the Finnish registry on persons with ID a cohort of  persons with a fragile X diagnosis during –. Follow-up for cancer incidence was performed in the Finnish Cancer Registry until the end of the year . Results There were  reported cancers during the mean follow-up of . years per person. The expected number of cancers based on the average Finnish population was . and no statistically sig- nificant protective effect was detected [standardised incidence ratios (SIR) ., confidence interval (CI) % .–.]. An increased risk for lip cancer was found (SIR , CI % .–). Conclusions Confirmation of hypotheses about the mechanisms linking FXS and cancer needs further research. Keywords cancer, fragile X syndrome, incidence, intellectual disability Introduction Fragile X syndrome (FXS) is a common inheritable cause of intellectual disability (ID). In FXS a person has regions in X-chromosome prone to breakage (Verkerk et al. ). A full mutation with more than  repeats typically disables the activity of the FMR gene and the expression of the FMR protein (FMRP). FMRP is a selective RNA-binding protein implicated in regulating translation of its mRNA ligands. The functional absence of FMRP leads to ID as well as to different learning and emo- tional problems without necessarily severe cognitive deficits (Hagerman PJ ). The physical phenotype in FXS includes a long face, prominent ears, a high-arched palate, hyperex- tensible finger joints, double-jointed thumbs, flat feet and macroorchidism (Merenstein et al. ; Hagerman RJ ). A recurrent otitis media and an attention-deficit hyperactivity disorder are medical problems that are encountered among more than two-thirds of persons with FXS (Hagerman RJ ). FMRP is an mRNA carrier protein, but it is not known whether the FXS phenotype is due to Correspondence: Dr Reijo Sund, National Research and Develop- ment Centre forWelfare and Health (STAKES), PO Box , FI- Helsinki, Finland (e-mail: reijo.sund@stakes.fi). Journal of Intellectual Disability Research doi: 10.1111/j.1365-2788.2008.01116.x 1 ©  The Authors. Journal Compilation ©  Blackwell Publishing Ltd