Behavioral abnormalities in the Fmr1-KO2 mouse model of fragile X syndrome: The relevance of early life phases.
In fragile X mice social deficits vanish after youth, so test early or miss them.
01Research in Context
What this study did
Gaudissard et al. (2017) watched Fmr1-KO2 mice grow up. These mice lack the fragile X gene.
They tracked social, repetitive and anxiety-like behaviors from babyhood to adulthood.
What they found
Social problems showed up only in early life. By adolescence the mice looked typical.
Other fragile-X signs stayed across ages. Repetitive jumping and mild anxiety remained.
How this fits with other research
Capio et al. (2013) also saw weak social change in standard Fmr1 knockouts, but only when the pups were raised alone. Julie’s group used group-housed KO2 mice and still caught early-only social deficits, showing the timing matters more than rearing.
Mottolese et al. (2024) tested a different autism model (Cdkl5-KO) and found social deficits that lasted into adulthood. The contrast warns us that fragile X social problems close early, while some other gene models stay open for longer testing windows.
Guy et al. (2020) moved the story to children with fragile X. Kids showed less initial looking at social items, matching the early-only mouse pattern. Together the papers flag infancy-toddlerhood as the key window for social attention in FXS.
Why it matters
If you screen or treat fragile X, test social skills before school age. Waiting until later may miss the problem and underestimate need. Mouse and human data now line up: early childhood is when social symptoms peak.
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02At a glance
03Original abstract
Fragile X syndrome (FXS) is a developmental disorder caused by a mutation in the X-linked FMR1 gene, coding for the FMRP protein which is largely involved in synaptic function. FXS patients present several behavioral abnormalities, including hyperactivity, anxiety, sensory hyper-responsiveness, and cognitive deficits. Autistic symptoms, e.g., altered social interaction and communication, are also often observed: FXS is indeed the most common monogenic cause of autism. Mouse models of FXS are therefore of great interest for research on both FXS and autistic pathologies. The Fmr1-KO2 mouse line is the most recent FXS model, widely used for brain studies; surprisingly, little is known about the face validity of this model, i.e., its FXS-like behavioral phenotype. Furthermore, no data are available for the age-related expression of the pathological phenotypes in this mouse line, a critical issue for modelling neurodevelopmental disorders. Here we performed an extensive behavioral characterization of the KO2 model at infancy, adolescent and adult ages. Hyperactivity, altered emotionality, sensory hyper-responsiveness and memory deficits were already present in KO mice at adolescence and remained evident at adulthood. Alterations in social behaviors were instead observed only in young KO animals: during the first 2 weeks of life, KOs emitted longer ultrasonic vocalizations compared to their WT littermates and as adolescents they displayed more aggressive behaviors towards a conspecific. These results strongly support the face validity of the KO2 mouse as a model for FXS, at the same time demonstrating that its ability to recapitulate social autistic-relevant phenotypes depends on early testing ages. Autism Res 2017, 10: 1584-1596. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.
Autism research : official journal of the International Society for Autism Research, 2017 · doi:10.1002/aur.1814