title: Detection of mosaic RB1 mutations in families with retinoblastoma.
abstract: The RB1 gene mutation detection rate in 1,020 retinoblastoma families was increased by the use of highly sensitive allele specific-PCR (AS-PCR) to detect low-level mosaicism for 11 recurrent RB1 CGA>TGA nonsense mutations. For bilaterally affected probands, AS-PCR increased the RB1 mutation detection sensitivity from 92.6% to 94.8%. Both RB1 oncogenic changes were detected in 92.7% of sporadic unilateral tumors (357/385); 14.6% (52/357) of unilateral probands with both tumor mutations identified carried one of the tumor mutations in blood. Mosaicism was evident in 5.5% of bilateral probands (23 of 421), in 3.8% of unilateral probands (22 of 572), and in one unaffected mother of a unilateral proband. Half of the mosaic mutations were only detectable by AS-PCR for the 11 recurrent CGA>TGA mutations, and not by standard sequencing. This suggests that significant numbers of low-level mosaics with other classes of RB1 mutations remain unidentified by current technology. We show that the use of linkage analysis in a two-generation retinoblastoma family resulted in the erroneous conclusion that a child carried the parental mutation, because the founder parent was mosaic for the RB1 mutation. Of 142 unaffected parental pairs tested, only one unaffected parent of a proband (0.7%) showed somatic mosaicism for the proband's mutation, in contrast to an overall 4.5% somatic mosaicism rate for retinoblastoma probands, suggesting that mosaicism for an RB1 mutation is highly likely to manifest as retinoblastoma.
authors.affiliation: Retinoblastoma Solutions, Toronto Western Hospital, Toronto, Ontario, Canada.
authors.forename: Diane
authors.initials: D
authors.lastname: Rushlow
authors.forename: Beata
authors.initials: B
authors.lastname: Piovesan
authors.forename: Katherine
authors.initials: K
authors.lastname: Zhang
authors.forename: Nadia L
authors.initials: NL
authors.lastname: Prigoda-Lee
authors.forename: Mellone N
authors.initials: MN
authors.lastname: Marchong
authors.forename: Robin D
authors.initials: RD
authors.lastname: Clark
authors.forename: Brenda L
authors.initials: BL
authors.lastname: Gallie
mesh_terms: D001483:Base Sequence; D004252:DNA Mutational Analysis; D005260:Female; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009030:Mosaicism; D009154:Mutation / Q000235:genetics*; D016133:Polymerase Chain Reaction; D012175:Retinoblastoma / Q000235:genetics*; D016160:Retinoblastoma Protein / Q000235:genetics*
chemical_list: D016160:Retinoblastoma Protein