Redcay Elizabeth, Courchesne Eric
Department of Psychology, University of California, San Diego, USA.
Biol Psychiatry. 2005 Jul 1;58(1):1-9. doi: 10.1016/j.biopsych.2005.03.026.
Multiple studies have reported increased brain size in autism, while others have found no difference from normal. These conflicting results may be due to a lack of accounting for age-related changes in brain enlargement, use of small sample sizes, or differences in data acquisition methods.
Reports of autism head circumference (HC), magnetic resonance imaging (MRI), and post-mortem brain weight (BW) that met specific criteria were identified and analyzed. Percent difference from normal values (%Diff) and standardized mean differences (SMD) were calculated to compare brain size across studies and measurement methods. Curve fitting, analysis of variance, and heterogeneity analyses were applied to assay the effects of age and measurement type on reported brain size in autism.
A fitted curve of HC and MRI %Diff values from 15 studies revealed a largely consistent pattern of brain size changes. Specifically, brain size in autism was slightly reduced at birth, dramatically increased within the first year of life, but then plateaued so that by adulthood the majority of cases were within normal range. Analysis of variance of MRI and post-mortem %Diff values by age group (young child, older child, adult) and measurement type (MRI, BW) revealed a significant main effect of both age and measurement type, with the youngest ages (2-5) showing the greatest deviation from normal. Random effects heterogeneity analysis revealed a significant effect of age on HC and MRI SMD.
These findings reveal a period of pathological brain growth and arrest in autism that is largely restricted to the first years of life, before the typical age of clinical identification. Study of the older autistic brain, thus, reflects the outcome, rather than the process, of pathology. Future research focusing on this early process of brain pathology will likely be critical to elucidate the etiology of autism.
多项研究报告称自闭症患者大脑体积增大，而其他研究则发现与正常人并无差异。这些相互矛盾的结果可能是由于未考虑与年龄相关的大脑增大变化、样本量过小或数据采集方法的差异。
识别并分析符合特定标准的自闭症头围（HC）、磁共振成像（MRI）和尸检脑重量（BW）报告。计算与正常值的百分比差异（%Diff）和标准化平均差异（SMD），以比较不同研究和测量方法之间的大脑大小。应用曲线拟合、方差分析和异质性分析来测定年龄和测量类型对自闭症患者报告的大脑大小的影响。
来自15项研究的HC和MRI %Diff值拟合曲线显示出大脑大小变化的基本一致模式。具体而言，自闭症患者的大脑大小在出生时略有减小，在生命的第一年内急剧增加，但随后趋于平稳，因此到成年时，大多数病例处于正常范围内。按年龄组（幼儿、年长儿童、成人）和测量类型（MRI、BW）对MRI和尸检%Diff值进行方差分析，结果显示年龄和测量类型均有显著的主效应，最年幼的年龄组（2 - 5岁）与正常的偏差最大。随机效应异质性分析显示年龄对HC和MRI SMD有显著影响。
这些发现揭示了自闭症患者大脑病理生长和停滞的时期，这主要局限于临床确诊的典型年龄之前的生命最初几年。因此，对大龄自闭症患者大脑的研究反映的是病理结果，而非病理过程。未来聚焦于大脑病理这一早期过程的研究可能对于阐明自闭症的病因至关重要。
