TUBA1A and lissencephaly spectrum disorders: Table 5 provides TUBA1A mutations linked to microcephaly. In this review, we use the broadest definition of microcephaly and include cases where the OFC is 2 SD below the appropriate mean (i.e., less than the 3rd percentile). Using this classification, ~74% of TUBA1A mutations lead to “microcephaly”, or smaller than normal head size. It is important to note that microcephaly is never the primary cortical malformation associated with TUBA1A mutants, but is a common accompaniment to both lissencephaly and polymicrogyria cortical phenotypes.