Schwerwiegende kognitive Verzögerung mit fröhlichem Auftreten: Differentialdiagnose jenseits des Angelman-Syndroms

Several genetic syndromes combine severe intellectual disability with a notably happy, sociable affect. Differential includes:

1. Down Syndrome (Trisomy 21): Characteristic facies, hypotonia, congenital heart defects. Typically cheerful, affectionate.
2. Williams Syndrome (7q11.23 deletion): Elfin facies, cardiovascular disease, hypersociability, musicality, anxiety.
3. Prader-Willi Syndrome (15q11-q13 paternal deletion): Neonatal hypotonia, hyperphagia/obesity, mild-moderate ID, sweet temperament.
4. Fragile X Syndrome (FMR1 CGG expansion): Most common inherited ID; social anxiety but often friendly, eye contact avoidance.
5. Smith-Magenis Syndrome (17p11.2 deletion): Self-hugging, sleep disturbance, behavioral challenges, but often engaging affect.
6. Other: 22q13.3 deletion (Phelan-McDermid), ATR-X syndrome, etc.

Diagnosis requires: Clinical genetics evaluation, chromosomal microarray, targeted gene testing, and specialist assessment. Each syndrome has distinct medical management needs.