Fragile X Syndrome (FXS) is the leading known cause of inherited intellectual disability and results from a mutation of the FMR1 gene on the long arm of the X chromosome (Hagerman & Hagerman, 2002). In addition to cognitive delay, the behavioral phenotype of FXS often includes features of autism (e.g., poor eye contact, perseverative behavior) and attention-deficit/hyperactivity disorder (e.g., inattention, hyperactivity), as well as symptoms of social anxiety (Bailey et al., 2008; Hatton et al., 2002). Mothers of individuals with FXS report high levels of distress as compared to both the general population and to mothers of children with certain other disabilities (e.g., Down syndrome; Abbeduto et al., 2004; Sarimski, 1997; Wheeler et al., 2007); however, considerable variability in well-being exists (Poelhmann et al., 2003; Lewis et al., 2006). As is the case for mothers of children with other developmental disabilities (e.g., Davis & Carter, 2008; McIntyre et al., 2002), variability in well-being among mothers of individuals with FXS appears to be tied in part to behavioral characteristics of the child. Behavior problems in individuals with FXS have been associated with maternal stress and distress (e.g., depression, anxiety) in studies focusing on childhood, adolescence, and young adulthood (Abbeduto et al., 2004; Hall et al., 2007; Johnston et al., 2003; Wheeler, et al., 2007). Although the link between children’s behavior problems and poorer well-being in mothers of children with FXS is relatively well established, the degree to which behavior problems and poor maternal mental health might affect broader aspects of family functioning has been investigated less frequently. It is likely that maternal distress brought on and/or amplified by difficult child behavior might spillover beyond the parent-child dyad, challenging more distal dyadic relationships and the broader family climate (Bailey et al., 2007). The current study examined associations between behavior problems in adolescents and adults with FXS, maternal internalizing symptoms, and two key family outcomes: family cohesion and mothers’ marital satisfaction. One of the most studied aspects of interpersonal functioning within families of individuals with FXS has been family-level cohesion, or the closeness and supportiveness of the family unit. Johnston and colleagues (2003) found that behavior problems in a sample of children and adolescents with FXS were positively associated with aspects of maternal stress, which were, in turn, linked to lower family cohesion. Interestingly, behavior problems in this study were associated directly with family cohesion at the level of a trend only. Hall et al. (2007), found associations between children’s behavior problems and maternal internalizing symptoms (anxiety and depression), but did not find significant links between behavior problems and broad family functioning; however, cohesion was not examined specifically and the association between internalizing symptoms and the family environment was not a focus. The few findings to date suggest that either the behavior problems of individuals with FXS are unrelated to family cohesion or that the effects may be indirect, through compromised maternal well-being. To our knowledge, no study has examined the marital relationships of parents of individuals with FXS. Findings involving families of children with other developmental disabilities are mixed, suggesting that the presence of a child with a disability may or may not impart risk for poor marital functioning (see Hartley, Seltzer, Barker, et al., in press, for a review). Examinations of the correlates of marital functioning within families of children with developmental problems have produced somewhat mixed results. Baker and colleagues (2002) found that the behavior problems of preschoolers with developmental delays related to parents’ reports of a negative impact on their marriages. Kersh et al. (2006) reported an association between the behavior problems of 10-year-old children with developmental disabilities and marital quality for mothers but not for fathers. Depressive symptoms in this study were related to both child behavior, and to marital quality — again raising the possibility of indirect effects. Research and theory related to indirect effects in genetic syndromes has tended to focus on children’s behavior as a mechanism for associations between syndrome status and parental stress or coping (Hodapp, 1997; Hodapp & Dykens, 2009). The current study expands upon investigations of indirect effects between genotype and family response to examine potential pathways among specific areas of functioning within families of individuals with FXS. In addition to experiences shared with other families of children with developmental disabilities, families of individuals with FXS may also encounter unique challenges. Unlike many commonly studied developmental disorders, FXS has a known genetic inheritance linked to particular family members who themselves may exhibit certain vulnerabilities as a function of their carrier status (Bailey et al., 2008; Franke et al., 1998). Family interaction and communication around issues related to FXS are likely to be challenging for these families (Bailey, 2010), potentially complicating family dynamics and marital relations. The majority of studies on FXS and family process have focused on children and adolescents or very young adults with FXS (e.g., Abbeduto et al., 2004; Hall et al., 2007; Johnston et al., 2003; Lewis et al., 2006; Wheeler et al., 2007). However, changes in the FXS phenotype over time (Dykens et al., 2000) and in parenting challenges related to caring for an adult child with a disability (Seltzer et al., 2001), make consideration of family process in FXS important across the continuum of the family life cycle. Although considerable variability exists, many adults with FXS continue to require significant care (Bailey et al., 2009), and recent findings from our laboratory have linked the behavior of adolescents and adults with FXS to maternal daily stress, using daily diaries and cortisol measurement (MASKED). Understanding the pathways by which behavior problems might affect mental health and relationships in families of adolescents and adults with FXS could identify the most beneficial avenues for interventions aimed at improving the lives of these families. The Current Study We hypothesized that behavior problems in the individuals with FXS would be positively associated with maternal internalizing (i.e., depressive and anxiety) symptoms, which would, in turn, relate negatively to both marital satisfaction and family cohesion. Furthermore, we predicted significant indirect effects between behavior problems and the family relationship variables through maternal internalizing symptoms. The possibility of maternal internalizing symptoms as a pivotal mechanism for the influence of children’s behavior problems on families of individuals with FXS is particularly intriguing given the suggestion that maternal carrier status (i.e., the premutation of the FMR1 gene) may lead to increased risk for internalizing problems, above and beyond the effects of caring for a child with a disability (Bailey et al., 2008; Franke et al., 1998). The current study therefore accounted for variations in the genotype of the mothers (i.e., the number of CGG repeats) and focused only on mothers with the FMR1 premutation (CGG = 55 to 200), due to the qualitatively different phenotype of individuals with the full mutation (CGG > 200; Bailey et al., 2008; Hagerman & Hagerman, 2002). We also considered additional factors found or suspected to relate to our variables of interest (Abbeduto et al., 2004; Johnston et al., 2003; Seltzer et al., 2009).