Two syndromes associated with the same chromosomal region

Prader–Willi syndrome is characterized by
neonatal muscular weakness and feeding difficulties,
followed in early childhood by reduced
or lack of satiation control leading to massive
obesity in many patients. Several other, variable
features occur, such as mental retardation,
characteristic facial features, short stature, hypopigmentation,
behavioral problems, and
other findings. In Angelman syndrome the
developmental retardation is usually very
severe. Nearly total lack of speech development,
an abnormal electroencephalogram with tendency
to seizures, and hyperactivity are almost
always present.