NDE1 and lissencephaly spectrum disorders: Heterozygous deletions or mutations of LIS1 (also known as PAFAH1B1) result in lissencephaly (smooth brain) [2, 5, 18, 24, 46, 47, 61]; biallelic mutations or deletions in NDE1 have been shown to result in microcephaly (small brain) [46], microlissencephaly [2, 5] or microhydranencephaly [24].