CONCORDANCE BETWEEN PARENTAL ORIGIN OF CHROMOSOME 13Q LOSS AND CHROMOSOME 6P DUPLICATION IN SPORADIC RETINOBLASTOMA

Two hypotheses are capable of explaining nonrandom loss of one parent' s alleles at tumor suppressor loci in sporadic cases of several pediat ric cancers, including retinoblastoma-namely, preferential germ-line m utation or chromosome imprinting. We have examined 74 cases of sporadi c retinoblastoma for tumors in which at least two genetic events-loss of heterozygosity for chromosome 13q markers and formation of an isoch romosome 6p-have occurred. Sixteen cases were found to contain both ev ents. In 13 of 16 such tumors, the chromosomes 13q that were lost and chromosomes 6p that were duplicated are derived from the same parent. These data may be explained within the framework of the genome imprint ing model but are not predicted by preferential germ-line mutation.