More than 70% of Angelman syndrome (AS) cases are caused by a deletion in chromosome 15q11-13. The deletion is visualized  beautifully as a purple signal by the FISH-technique. In AS epilepsy is extremely common and this is related to a dysfunctional GABRB-3 –gene, causing a defect GABA-A receptor. Epilepsy in AS is highly responsive to GABA-ergic drugs like benzodiazepines. 

This is an example how making a correct diagnose can be helpful in planning optimal treatment.  

In  Hallervorden-Spatz syndrome a characteristic “eye of the tiger” appearance is seen on MR-imaging of the brain. The intense signal of the pallida is related to abnormal presence of iron in the basal ganglia.