12 Chapter 1 2. Restrictive and repetitive behavior Further potential precursors of early onset ASD include more pronounced repetitive behavior with objects and atypical body movement (Barber et al., 2012; Bryson et al., 2007; Lim et al., 2021; Matson et al., 2009; Miller et al., 2021; Patterson et al., 2022). However, it is important to note that restricted and repetitive behaviors are also part of typical development, especially in the first year of life (Arnott et al., 2010; Leekam et al., 2007). Later, stereotypical, restrictive and repetitive behaviors become more prominent. Toddlers with ASD may display hand and finger mannerisms, show repetitive interests, or play behavior, engage in self-injury behaviors (for example head banging), self-stimulatory use of objects, insistence on sameness, and/ or unusual sensory behaviors (for example hyper- or hyposensitivity to sounds, textures or other sensory stimuli). Non-specific markers, such as early motor impairments in the 0-24 month age range, encompassing differences in fine, gross, and generalized motor functions, have been identified in infants later diagnosed with autism (Lim et al., 2021). © P. Brouwers Note. These pictures illustrate a specific interest in toys and a fascination with spinning objects Importance of early detection and timely intervention of autism Over the last years there has been an increased scientific and clinical interest in the potential of early interventions changing developmental trajectories in young children with or at elevated likelihood of autism spectrum disorder (ASD) (French & Kennedy, 2018). Multiple studies show that intervening at an early age can have a positive impact on child development, on family and society functioning and cost-effectiveness (e.g. Dawson et al., 2012; Fuller & Kaiser, 2020; Horlin et al., 2014; Tinelli et al., 2023), although results of very early interventions vary amongst studies (Hamptom & Rodriguez, 2022; McGlade et
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