Autism
The brain size is increased, particularly in young autistic children. Bailey et al., 1998, reported cortical dysgenesis, increased neuronal density, presence of neurons in the molecular layer, and abnormal laminar patterns. Two-thirds of patients had white matter abnormalities. Minicolumns (radially arranged neurons, comprising the smallest level of functional organization in the cortex) were more numerous and narrower in autistic brains.
Cortical spine densities were higher in a subgroup of autistic individuals when compared to control subjects. A volumetric and density study found cerebellar volume deficits in the entire cerebellum by 19% (Wegiel, 2004). There was also a 41% decrease in Purkinje cells and in other structures of the motor system along with a decreased total number of neurons (Wegiel, 2004).
A study of eight types of neurotransmitter receptors from four systems (GABAergic, cholinergic, serotonergic, and glutamatergic) in the hippocampus showed a specific and substantial reduction in the GABAergic system (Blatt et al, 2001). GABA synthesis was also found to be significantly reduced in the parietal cortex and cerebellum (Fatemi et al., 2001).
Abnormalities in the development of amygdala–cortical connectivity, particularly with prefrontal regions that are associated with social information processing in autism have been suggested (Tager-Flusberg, Skwerer, Joseph, 2006)
Williams syndrome
In contrast to autism, in Williams syndrome, there is a reduction in the brain volume, preservation of cerebellum and frontal lobes, and a reduction of posterior cortical systems (Alleva et al., 1999).
Similar to autism, the amygdala dysfunction in Williams syndrome also involves abnormal connectivity, especially with the prefrontal regions required for social information processing (Tager-Flusberg, Skwerer, Joseph, 2006)
In one neuropathological study of a 35-year-old patient with Williams syndrome, there was the presence of Alzheimer-type changes (beta/A4 amyloid-containing senile plaques, scattered neurofibrillary tangles in neocortex and medial temporal lobe structures) (Golden et al., 1995.)
The plaques were most numerous in the amygdala and in the entorhinal cortex. Neurofibrillary tangles were less numerous, except in the hippocampus (Golden et al., 1995.)
In summary, both autism and William’s syndrome have common abnormalities in the development of amygdala–cortical connectivity. In contrast, the brain size in autism increased while there is a reduction in the brain volume in William’s syndrome. While there are cerebellar volume deficits in autism, there is the preservation of cerebellum and frontal lobes in William’s syndrome.
References
Alleva, E, Cirulli, F, Calamandrei, G, Rondinini, C, Capirci, O, Aloe, L, Volterra, V, 1999. Williams syndrome. Ann Ist Super Sanita. 35(2): 211-9.
Bailey, A, Luthert, P, Dean, A, 1998. A clinicopathological study of autism. Brain. 21:889–905.
Blatt, GJ, Fitzgerald, CM, Guptill, JT, 2001. Density and distribution of hippocampal neurotransmitter receptors in autism: An autoradiographic study. J Autism Dev Disord. 31:537–44.
Fatemi, SH, Stary, JM, Halt, AR, 2001. Dysregulation of Reelin and Bcl-2 proteins in autistic cerebellum. J Autism Dev Disord. 31:529–35.
Golden, JA, Nielsen, GP, Pober, BR, Hyman, BT, 1995. The neuropathology of Williams syndrome. Report of a 35-year-old man with presenile beta/A4 amyloid plaques and neurofibrillary tangles. Arch Neurol. 52(2):209-12.
Tager-Flusberg, H, Skwerer, DP, Joseph, RM. 2006.Model syndromes for investigating social cognitive and affective neuroscience: a comparison of autism and Williams syndrome. Social Cognitive and Affective Neuroscience. 1(3): 175-182.
Wegiel, J, 2004. Neuronal deficits in the motor system of people with autism with less pronounced pathology in the memory system. Abstract in the proceedings of the Integrating the Clinical and Basic Sciences of Autism: A Developmental Biology Workshop; Fort Lauderdale, Florida.