METABOLIC ABNORMALITIES IN DEVELOPMENTAL DYSLEXIA DETECTED BY H-1 MAGNETIC-RESONANCE SPECTROSCOPY

Background Neurological and physiological deficits have been reported in the brain in developmental dyslexia. The temporoparietal cortex has been directly implicated in dyslexic dysfunction, and substantial ind irect evidence suggests that the cerebellum is also implicated. We wan ted to find out whether the neurological and physiological deficits ma nifested as biochemical changes in the brain. Methods We obtained loca lised proton magnetic resonance spectra bilaterally from the temporo-p arietal cortex and cerebellum of 14 well-defined dyslexic men and 15 c ontrol men of similar age. Findings We found biochemical differences b etween dyslexic men and controls in the left temporo-parietal lobe (ra tio of choline-containing compounds [Cho] to N-acetylaspartate [NA] p less than or equal to 0.01) and right cerebellum (Cho/NA, p less than or equal to 0.01; creatine [Cre] to NA p less than or equal to 0.05; ( not significant). We found lateral biochemical differences in dyslexic men in both these brain regions (Cho/NA in temporo-parietal lobe, lef t vs right, p less than or equal to 0.01; Cre/NA in cerebellum, left v s right, p less than or equal to 0.001). We found no such lateral diff erences in controls. There was no significant relation between the deg ree of contralateral chemical difference and handedness in dyslexic or control men. Interpretation We suggest that the observed differences reflect changes in cell density in the temporo-parietal lobe in develo pmental dyslexia and that the altered cerebral structural symmetry in dyslexia is associated with abnormal development of cells or intracell ular connections or both. The cerebellum is biochemically asymmetric i n dyslexic men, indicating altered development of this organ. These di fferences provide direct evidence of the involvement of the cerebellum in dyslexic dysfunction.