In the developing brain, neural stem cells must migrate from the areas where they are born to the areas where they will settle into their proper neural circuits.<unk><unk> , which occurs as early as the second month of gestation, is controlled by a complex assortment of chemical guides and signals. When these signals are absent or incorrect, neurons do not end up where they belong. This can result in structurally abnormal or missing areas of the brain in the cerebral hemispheres, cerebellum, brainstem, or hippocampus. Several genetic abnormalities in children with<unk> s have been identified. Defects in genes that are involved in<unk><unk>  have been associated with<unk> s, but the role they play in the development of these disorders is not yet well understood. A study in Sweden investigated the impact of environmental factors on<unk> s. The study indicated that there might be an impact of low or subnormal maternal BMI before and during pregnancy, maternal infection, such as rubella, and maternal smoking on fetal brain development, including<unk><unk> . The roles of maternal BMI and congenital infections should be tested in future analytical studies.<unk> s occur in the instance that 1) neuroblasts do not migrate from all of the ventricles or migrate only part of the way, 2) only some of the neuroblasts reach the cortical layer, 3) neuroblasts overshoot the appropriate cortical layer and protrude into the subarachnoid space, or 4) the late stage organization of the<unk>  layer in the cortex is disrupted. Abnormal<unk>  ultimately results in abnormal gyral formation.
Neuronal migration disorder
Developmental regression
Peroxisomal disorder
Cranio-lenticulo-sutural dysplasia
Developmental disorder
Neuroectodermal neoplasm
Caudal regression syndrome
Trinucleotide repeat disorder