60-80% of pt's have interstit delet of 15q bands 11-13
origin of deleted chromosome is maternal (mnemonic: girls are angels, boys are hungry devils)
"genomic imprinting" = genes on 15q11q13q on maternally inherited chromosome are expressed differently from paternally inherited xsome
paternal uniparental disomy is a rare cause of the d/o
all cases are sporadic with exception of familial chromosomal rearrangement of Angelman locus

main features ("left handed, laughing puppet")
"puppet-like" gait
paroxyms of laughter
characteristic facies

Development: severe MR with motor delay (100%); profound speech deficit: absent speech or <6words
Head/Facies: microbrachycephaly; blond hair (65%); ocular abnormalities (decreased choroid/iris pigmentation -> resulting in pale blue eyes); deep set eyes; large mouth (macrostomia) protruding tongue/widely spaced teeth; maxillary hypoplasia and prognathia (prominent chin)
Coloring: ocular or skin hypopigmentation (pale eyes).
Behavior: paroxysms of inappropriate laugher often accompanied by hand flapping; hyperactivity; ataxia/jerky arm movemts (~ puppet gait; 100%, becomes apparent around time child begins to sit); arms in characteristic position (upheld with wrist/elbow flexion)
Neuro stuff: seizures (variable type; usually begin 18-24mos; 86%; relatively easy to control); characteristic EEG findings; hypotonia c occas hyperreflexia; cerebral atrophy (33%)
L hand preference

natural hx
MR is nonprogressive but severe
sz's most severe ~4yrs; may stop by 10yrs
laughter NOT assoc c happiness but probable brain stem abnL
decr sleep from 2-6yrs
vast majority communicate nonverbally (eg, sign language)
may be able to follow simple commands

CHLA board review course 2005
Baraitser and Winter, 1996. Color Atlas of Congenital Malformation Syndromes