Positron emission tomography methods with potential for increased understanding of mental retardation and developmental disabilities

Positron Emission Tomography (PET) Quantification of GABAA Receptors in the Brain of Fragile X Patients

Over the last several years, evidence has accumulated that the GABAA receptor is compromised in animal models for fragile X syndrome (FXS), a common hereditary form of intellectual disability. In mouse and fly models, agonists of the GABAA receptor were able to rescue specific consequences of the fragile X mutation. Here, we imaged and quantified GABAA receptors in vivo in brain of fragile X patients using Positron Emission Topography (PET) and [11C]flumazenil, a known high-affinity and specific ligand for the benzodiazepine site of GABAA receptors. We measured regional GABAA receptor availability in 10 fragile X patients and 10 control subjects. We found a significant reduction of on average 10% in GABAA receptor binding potential throughout the brain in fragile X patients. In the thalamus, the brain region showing the largest difference, the GABAA receptor availability was even reduced with 17%. This is one of the first reports of a PET study of human fragile X brain and directly demonstrates that the GABAA receptor availability is reduced in fragile X patients. The study reinforces previous hypotheses that the GABAA receptor is a potential target for rational pharmacological treatment of fragile X syndrome.

Are incidental findings on brain magnetic resonance images in children merely incidental?

The purpose of this study was to test the hypothesis that children with developmental delay without regression of unknown etiology are more likely to have intracranial incidental findings than are children with autistic spectrum disorder or children with normal development. Of 771 patients with magnetic resonance images, 363 (47.1%) patients had developmental delay, 55 (7.1%) had autistic spectrum disorders, and 353 (45.8%) were developmentally normal. Developmentally delayed children were more likely than those with normal development (odds ratio [OR], 1.8; 95% confidence interval [CI], 1.3-2.5; P < .001) or those with autistic spectrum disorder (OR, 2.1; 95% CI, 1.1-4.1; P = .019) to have an intracranial incidental finding. We report a higher prevalence of intracranial incidental findings in children with developmental delay as compared with those children with normal development. Future study should confirm whether the result of this study is merely incidental or truly related to a subgroup of children with developmental disability.