Molecular characterization of the deletion in retinoblastoma patients with 13q14 cytogenetic anomalies.

We investigated the molecular deletions of twelve patients presenting with retinoblastoma and a cytogenetic abnormality including band 13q14. Dinucleotide markers spanning the complete chromosome 13 as well as two intragenic markers were analyzed in patients and their two parents. The deletion was considered confirmed when one heterozygous allele was missing, potential when a homozygous allele was observed in continuity with a clearly deleted allele, and noninformative when a homozygous allele was observed adjacent to a nondeleted region. The patients could be classified into three groups based on their cytogenetic abnormalities. In group 1, the cytogenetic deletion was restricted to band13q14 with confirmed or potential molecular deletions extending from D13S328 to D13S153. Although a possible common centromeric deletion breakpoint could exist for three of the patients and a common telomeric deletion breakpoint for two, the cytogenetic deletion was different for most of them. Group 2 included patients with a cytogenetic deletion extending up to 13q22. At the molecular level, the telomeric breakpoints were between the RB1 gene and D13S156. Here again, it is quite unlikely that a common telomeric breakpoint was responsible for the deletion. Group 3 consisted of special cases with either a paracentric inversion or a complex translocation. The cytogenetic abnormalities around 13q14 correlate with the molecular deletions that were observed in this study. Associated malformations cannot be easily predicted from the size of the deletions.