What is the diagnosis?
Double cortex syndrome (also known as band heterotopia).
What other congenital cortical malformation is associated with subcortical band heterotopia?
Lissencephaly type I (classic). In fact the two conditions are due to similar mutations and form a spectrum.
What is the most common genetic abnormality and what impact does it have on demographics of affected individuals?
DXC gene located on the X chromosome tends to present as band heterotopia in females, whereas in males it presents with lissencephaly.
MRI of an 8 year old demonstrates a continuous ribbon of grey matter seen just deep to the cortex, separated from it with a thin layer of white matter. The overlying brain demonstrates some shallowness of sulci. Incidental cavum septum pellucidum et vergae is noted.