Chromosomal region 15q11–13 and imprinting center

Five genes known to date are transcribed from
the paternal allele only, not from the maternal
allele where they are constitutively repressed
(blue squares). From the more distal gene
UBE3A (a ubiquitin-protein ligase E3) only the
maternal allele is transcribed. About 25% of
cases of Angelman syndrome are caused by
deletion or mutation of this gene. The breakpoints
of the common large deletions occur predominantly
in three breakpoint cluster regions.
The imprinting center (IC) was originally defined
by small deletions outside of the known
imprinted genes. About 1% of patients with
PWS and 4% with AS have imprinting center defects.
The imprinted region on 15q11–13 shows
a difference in methylation pattern between the
maternal and the paternal allele. This is the
basis of a diagnostic test.
(Data in E. kindly provided by Dr. Karin Buiting).
Other imprinted chromosomal regions are also
associatedwithhumandiseases, e.g.,Beckwith–
Wiedemann syndrome and some patients with
Russell–Silver syndrome, among others.