Classifications
The degree of cerebral cortex malformation caused by genetic mutations is classified by the degree of malposition and the extent of faulty grey matter differentiation.Neuronal migration disorders are generally classified into three groups:

lissencephaly/subcortical band heterotopia
cobblestone
‘other’ heterotopias The ‘other’ types are associated with corpus callosum agenesis or cerebellar hypoplasia while the cobblestone lissencephalies are associated with eye and muscle disorders.Classical lissencephaly, also known as type I or generalized agyria-pachygyria, is a severe brain malformation of a smooth cerebral surface, abnormally thick (10-20mm) cortex with four layers, widespread neuronal heterotopia, enlarged ventricles, and agenesis or malformation of the corpus callosum. Classical lissencephaly can range from agyria to regional pachygyria and is usually present along with subcortical band heterotopia (known as ‘double cortex’ to describe the circumferential bands of heterotopic neurons located beneath the cortex). Subcortical band heterotopia is a malformation slightly different from lissencephaly that is now classified under the agyria-pachygyria-band spectrum because it consists of a gyral pattern consistent with broad convolutions and an increased cortical thickness. The established classification scheme for lissencephaly is based on the severity (grades 1-6) and the gradient. Grade 1: generalized agyria
Grade 2: variable degree of agyria
Grade 3: variable degree of pachygyria
Grade 4: generalized pachygyria
Grade 5: mixed pachygyria and subcortical band heterotopia
Grade 6: subcortical band heterotopia alone
Gradient ‘a’: from posterior to anterior gradient
Gradient ‘b’: from anterior to posterior gradient Grade 1 and Grade 4 are very rare. Grade 2 is observed in children with Miller–Dieker syndrome (a combination of lissencephaly with dysmorphic facial features, visceral abnormalities, and polydactyly).
"While NVLD is not classified into any distinct diagnosis in DSM-5 (American Psychiatric Association, 2013) or ICD-10 (World Health Organization, 1992), it does have a robust research base." "The majority of researchers and clinicians agree that the profile of NLD clearly exists...but they disagree on the need for a specific clinical category and on the criteria for its identification." (One researcher notes, "just because we cannot reasonably place such children into our present classification scheme does not mean they do not exist.") Assorted diagnoses have been discussed as sharing symptoms with NVLD. In some cases, especially the form of autism previously called Asperger syndrome, the overlap can be so significant as to render NVLD a pointless duplication in the mind of its detractors, with the only difference being that NVLD criteria do not mention the presence or absence of either repetitive behaviors or narrow subject-matter interests. (These are not required for a diagnosis of autism.) These overlapping conditions include, among others:

attention deficit hyperactivity disorder (ADHD)
autism spectrum disorders, especially high-functioning autism
developmental coordination disorder
social communication disorder
right hemisphere brain damage and developmental right hemisphere syndrome
social-emotional processing disorder
Gerstmann syndromeThere is diagnostic overlap between nonverbal learning disorder and autism spectrum disorder, and some clinicians and researchers consider them to be the same condition. In clinical settings, some diagnoses of attention deficit hyperactivity disorder would be more appropriately classified as NVLD.