Studies of infant siblings of older autistic probands, who are at elevated risk for autism, have demonstrated that the defining features of autism are not present in the first year of life but emerge late in the first and into the second year. A recent longitudinal neuroimaging study of high-risk siblings revealed a specific pattern of brain development in infants later diagnosed with autism, characterized by cortical surface area hyper-expansion in the first year followed by brain volume overgrowth in the second year that is associated with the emergence of autistic social deficits. Together with new observations from genetically defined autism risk alleles and rodent model, these findings suggest a conceptual framework for the early, post-natal development of autism. This framework postulates that an increase in the proliferation of neural progenitor cells and hyper-expansion of cortical surface area in the first year, occurring during a pre-symptomatic period characterized by disrupted sensorimotor and attentional experience, leads to altered experience-dependent neuronal development and decreased elimination of neuronal processes. This process is linked to brain volume overgrowth and disruption of the refinement of neural circuit connections and is associated with the emergence of autistic social deficits in the second year of life. A better understanding of the timing of developmental brain and behavior mechanisms in autism during infancy, a period which precedes the emergence of the defining features of this disorder, will likely have important implications for designing rational approaches to early intervention.

中文翻译：

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建立自闭症早期大脑和行为发展的概念框架。

对自闭症风险较高的年龄较大的自闭症先证者的兄弟姐妹进行的研究表明，自闭症的定义特征并不存在于生命的第一年，而是出现在第一年和第二年的后期。最近对高危兄弟姐妹进行的纵向神经影像学研究发现，后来被诊断为自闭症的婴儿的大脑发育有特定的模式，其特征是第一年皮质表面积过度膨胀，第二年大脑体积过度增长，这与患儿的大脑发育有关。自闭症社会赤字的出现。这些发现与遗传定义的自闭症风险等位基因和啮齿动物模型的新发现一起，为自闭症的出生后早期发展提供了概念框架。该框架假设在症状发生前的第一年神经祖细胞的增殖增加和皮质表面积的过度膨胀，其特征是感觉运动和注意体验受到破坏，从而导致依赖于经验的神经元发育发生改变。减少神经元过程的消除。该过程与大脑体积过度生长和神经回路连接的精细化破坏有关，并与第二年生命中自闭症社会缺陷的出现有关。更好地了解婴儿期（该疾病的定义特征出现之前的一个时期）自闭症的发育性大脑的时机和行为机制，