Neuroimaging studies in Rett syndrome.

Neuroimaging is a key instrument for determining structural and in vivo functional status of the brain, non-invasively. Multiple approaches can now determine aspects of anatomic and neurochemical changes in brain, and have been utilized effectively in Rett Syndrome patients to understand the biological basis of this neurodevelopmental disorder. Studies performed at our institute include volumetric analyses of MRI, magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), cerebral blood flow measurements with MRI, and positron emission tomography scans (PET). These studies have provided considerable insight into mechanisms underlying the clinical features of this disease. Volumetric analyses suggest that decreased brain volume in RS results from global reductions in both gray and white matter of the brain. A selective vulnerability of the frontal lobes is evidenced by the preferential reduction of blood flow, increased choline and reduced n-acetyl aspartate (NAA) by MRS, and increased glucose uptake in these same regions as shown by ((18)F)-fluorodeoxyglucose (FDG) PET scans. We hypothesize that the increased glucose uptake relates to increased glutamate cycling in synapses. The resulting neuroexcitotoxic injury to the developing brain contributes to the seizures, behavioral disturbance and respiratory irregularities commonly seen in phases 1 and 2 of this disorder.