Introduction: The aetiology of autosomal dominant mental retardation type 1, also known as pseudo-Angelman, MBD5-associated neurodevelopmental disorder or MBD5 haploinsufficiency, lies in a microdeletion of chromosome 2q23.1 or in a specific alteration of the MBD5 gene, which constitutes the minimum region affected in the aforementioned microdeletion.  Aim: To report the case of a girl with a heterozygous de novo mutation in the MBD5 gene associated with bilateral band heterotopia and polymicrogyria.  Case report: We report the case of an 8-year-old girl who was submitted to a developmental follow-up from the age of 18 months after presenting the association of severe intellectual disability and motor delay, lack of language development, segmental hypotonia, a wide forehead and kyphoscoliosis. Magnetic resonance imaging of the brain revealed the presence of a bilateral band heterotopia and parietooccipital polymicrogiria predominant on the left side. In the exome the de novo heterozygous variant c.397+1G>C was detected in the MBD5 gene.  Conclusion: This is the first observation of a heterozygous mutation in the MBD5 gene associated with a neuronal migration disorder.