Transcript 2B of RB1 is imprinted and paternally expressed whereas the main RB1 transcript shows
preferential maternal expression (Kanber
D et al, 2009). A DMR (PPP1R26P1) within a 1.2 kb CpG island (CpG 85) within intron 2 of RB1 is
from a retrotransposition of part of exon 3 and exon 4 of PPP1R26 (KIAA0649). In 5 individuals this
CpG island was methylated on the maternal allele and unmethylated on the paternal allele. CpG island
85 contains a novel start exon (2B). Limited evidence suggests paternal expression of the
2B-transcript which is postulated to interfere with the paternal full length RB1 transcript.
Nakabayashi K et al (2011) confirmed
maternal methylation of the maternal RB1 allele.
Prickett AR et al (2015) reported
hypermethylation of a CpG island (1 kb from the reported DMR) in 13/18 patients with Silver Russell
Previous evidence suggested the retinoblastoma gene itself does not appear to be imprinted, but there
may be parent-of-origin effects on the transmission of retinoblastoma susceptibility in humans (Naumova
A et al, 1994), and in mice (earlier onset of tumours when mutant Rb is paternally inherited)
AY et al, 1997). In isolated unilateral retinoblastoma, tumours having loss of the maternally
derived RB1 allele had an
earlier age of onset than those having paternal loss (Schuler A et al, 2005).
In an unexplained observation, the parental origin of a chromosomal rearrangement near RB affected
the NruI restriction enzyme
digestion pattern (Blanquet V et al, 1991).
De novo mutations of RB preferentially occur during male gametogenesis - this is not usually
regarded as an imprinting effect (see parental origin of de novo mutations section of this database).