OBJECTIVE The diagnosis of autism spectrum disorder (ASD) has been found to be remarkably stable but few studies have followed children not initially diagnosed with ASD beyond 3 years of age to examine late or delayed diagnoses. The present study used a prospective familial-risk design to identify children who had undergone multiple comprehensive assessments in preschool and were determined to be negative for ASD only to meet criteria for ASD when tested in middle childhood. METHOD Data were pooled across 3 research teams studying later-born siblings of children with ASD. Fourteen children met inclusion criteria for the late-diagnosed group and were compared with a large sample of high- and low-risk siblings from the same sites who had ASD or typical development (TD) outcomes at 3 years of age. RESULTS As a group, the late-diagnosed children scored between the TD and ASD groups on most measures administered at 3 years and differed significantly from the ASD group on most measures. However, there was significant heterogeneity among the late-diagnosed cases. Seven showed very little evidence of ASD in preschool, whereas 7 demonstrated subtle, subthreshold symptomatology. CONCLUSION Some children with ASD might present with a subtle phenotype early in life or show a prolonged time course of symptom development. This emphasizes the need for screening and surveillance schedules that extend past 36 months and continued evaluation of any child who presents with atypical early development and/or high-risk status. The findings also shed light on reasons why the mean age of ASD diagnosis remains older than 4 years.

中文翻译：

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纵向评估自婴儿期以来5岁儿童的自闭症谱系障碍的诊断。

目的发现自闭症谱系障碍（ASD）的诊断非常稳定，但很少有研究对最初未诊断出患有ASD的3岁以上的儿童进行晚期或延迟诊断。本研究使用前瞻性家族风险设计来识别在学龄前接受过多次综合评估的儿童，并确定其对ASD呈阴性，仅在儿童中期进行测试时才符合ASD的标准。方法收集了3个研究小组的数据，这些研究小组研究了ASD儿童的后代兄弟姐妹。14名儿童符合晚期诊断组的入选标准，并与来自同一地点且在3岁时具有ASD或典型发育（TD）结果的高风险和低风险兄弟姐妹的大量样本进行了比较。结果作为一个整体，在3年时进行的大多数测量中，晚期诊断的儿童在TD和ASD组之间得分，并且在大多数测量方面与ASD组显着不同。但是，在晚期诊断的病例中存在明显的异质性。7名儿童在学龄前表现出极少的ASD证据，而7名儿童表现出微妙的亚阈值症状。结论一些自闭症儿童可能在生命早期表现出细微的表型或表现出较长的症状发展过程。这强调了需要进行超过36个月的筛查和监视计划，并持续评估表现出非典型早期发育和/或高危状态的任何儿童。该发现还阐明了为什么ASD诊断的平均年龄仍大于4岁的原因。