MVA1 type 1 (OMIM 257,300) is caused by homozygous or compound heterozygous mutations in the BUB1B gene (OMIM 602,860) located in chromosome 15q1 and is clinically characterized by microcephaly, developmental delay/intellectual disability (DD/ID), epileptic seizures, generalized hypotonia, intrauterine growth restriction (IUGR), and postnatal growth retardation. Here, BUB1B is linked to microcephaly.