这一时期的遗传和环境的任何异常因素均可导致神经元移行障碍，例如脑裂畸形（schizencephaly）、无脑回（lissencephaly）、多小脑回（polymicrogyria）以及灰质异位（heterotopia），临床常表现为智力和运动发育障碍及惊厥发作。
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