18F-FDG PET brain findings in disease-discordant monozygotic mosaic twins with Cri du Chat (5p-) syndrome.

We describe the first report on the genotype-phenotype patterns and [18F] fluoro-deoxygluycose ( ¹⁸ F-FDG) Positron Emission Tomography (PET) findings in two disease-discordant monozygotic twins with Cri du Chat syndrome (CdcS) presenting deletion of 5p, 46, XY, del(5)(p14)/46, XY. One twin showed a severe phenotype; significant ¹⁸ F-FDG PET hypometabolism (p=0.001) was revealed in the left and right hemispheres, thalamus, cerebellum, and midbrain, whereas hypermetabolism was detected in the left premotor cortex. The other twin presented a mild phenotype; significant hypometabolism was detected only in the right side (parahippoccampal gyrus and cerebellum). Further studies should investigate the causes of phenotypic discordance in twins with CdcS.