Initially, researchers proposed that Fragile X syndrome (FXS) should be called AFRAX syndrome because it was thought to be caused by an autism gene (Gillberg, Persson, & Wahlström, 1986). However, as research into FXS has progressed and an exploration of the behavioural phenotype has taken place important differences have emerged. The systematic review (Paper 1) aims to delineate a behavioural phenotype for Fragile X Syndrome (FXS). Ten papers were included in the review. All papers were of a standard to demonstrate a behavioural phenotype for FXS. There are attributes of the FXS behavioural phenotype that meet the criteria for both Attention Deficit Hyperactive Disorder (ADHD) and/or Autism Spectrum Condition (ASC). However, there is robust evidence to support a broad FXS behavioural phenotype comprising: 1) social behavioural and communication difficulties, 2) emotional regulation difficulties, 3) repetitive and restrictive behaviour and speech. Several recommendations for research and clinical practice are discussed. The aim of the empirical study (paper 2) was to examine if there are differences between the behaviour phenotype profiles of those with FXS who have a diagnosis of ASC and those that do not. Parents were asked to complete an online questionnaire that included the Social Responsiveness Scale (SRS), the Wessex Questionnaire, and standard demographic information. The findings of the 38 parents who completed the questionnaire are discussed below. Finally, the research review (Paper3) will explore the author’s research process. This includes a discussion about the decisions to undertake the research, as well as a review of the methodological limitations, implications for policy direction, further research and clinical implications.