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 derived 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 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.
Maternal methylation of CpG 85 has been confirmed by Nakabayashi K et al (2011) and Eloy P et al (2016).
Prickett AR et al (2015) reported hypermethylation of a CpG island (1 kb from the reported DMR) in 13/18 patients with Silver Russell syndrome.
Previous evidence suggested 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) (Nikitin AY et al, 1997). This parent of origin effect may be more prominent for hypomorphic alleles (Eloy P et al, 2016; Imperatore V et al, 2018).
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).


Imprinted genes



Last Modified 4/23/2018


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