lissencephaly spectrum disorders (MONDO_0018838) is the term lissencephaly covers a group of rare malformations sharing the common feature of anomalies in the appearance of brain convolutions (characterized by simplification or absence of folding) associated with abnormal organization of the cortical layers as a result of neuronal migration defects during embryogenesis. Also known as: Lissencephaly, lissencephaly, lissencephaly (disease).