TMTC3-related syndrome is an autosomal recessive disorder resulting in intellectual disability, psychomotor retardation and absent speech. Affected individuals also exhibit microcephaly, muscular hypotonia and seizures. Interestingly, while its allelic disorder, 'Lissencephaly 8' (OMIM 617255) has been associated with neuronal migration defects such as cobblestone lissencephaly or periventricular hypertopia, TMTC3-related syndrome does not present with these anomalies.