The characterizing features of autism spectrum disorder (ASD) are continuously distributed in nature; however, prior twin studies have not systematically incorporated this knowledge into estimations of concordance and discordance. We conducted a quantitative analysis of twin–twin similarity for autistic trait severity in three existing data sets involving 366 pairs of uniformly-phenotyped monozygotic (MZ) twins with and without ASD. Probandwise concordance for ASD was 96%; however, MZ trait correlations differed markedly for pairs with ASD trait burden below versus above the threshold for clinical diagnosis, with R²s on the order of 0.6 versus 0.1, respectively. Categorical MZ twin discordance for ASD diagnosis is rare and more appropriately operationalized by standardized quantification of twin–twin differences. Here we provide new evidence that although ASD itself is highly heritable, variation-in-severity of symptomatology above the diagnostic threshold is substantially influenced, in contrast, by non-shared environmental factors which may identify novel targets of early ASD amelioration.

自闭症谱系障碍（ASD）的特征在自然界中是连续分布的；然而，先前的双生子研究并未系统地将该知识纳入对一致性和不一致性的估计中。我们在三个现有数据集中，对366对具有和没有ASD的统一表型单合子（MZ）双胞胎进行了自闭症特征严重程度的双胞胎相似性定量分析。ASD的先行一致性为96％；然而，对于ASD特质负荷低于或高于临床诊断阈值的配对，MZ特质相关性显着不同，R ²s分别为0.6和0.1的数量级。用于ASD诊断的分类MZ孪生不一致是罕见的，并且可以通过对孪生孪生差异的标准化量化来更适当地加以操作。在这里，我们提供了新的证据，尽管ASD本身具有很高的遗传力，但高于诊断阈值的症状严重程度变化却受到非共享环境因素的显着影响，这些环境因素可能会确定ASD早期缓解的新目标。