Siblings of retinoblastoma patients: Are we underestimating their risk?

PURPOSE: To describe the clinical presentation of probable germ-line mosaic ism in four retinoblastoma kindreds. METHODS: Review of 255 retinoblastoma patients and their family records in a University of California, San Francisco-Bascom Palmer database to identif y those with potential germ-line mosaicism. Parents and siblings of retinob lastoma patients were given comprehensive ophthalmologic examinations. RESULTS: Four kindreds were identified, wherein retinoblastoma was diagnose d in two siblings and both parents demonstrated no evidence of retinoblasto ma or retinocytoma. CONCLUSION: Clinical appearance of germ-line mosaicism is demonstrated in o ur retinoblascoma patient populations. We recommend routine clinical screen ing of all parents and siblings of retinoblastoma patients to provide more accurate genetic counseling and to allow earlier examination and treatment of children at presymptomatic disease stages. Germ-line mosaicism must be c onsidered as a genetic transmission pattern in these patients, and genetic counseling should specifically recognize this possibility. If a parent is g erm-line mosaic, the possibility of bearing a second child with retinoblast oma is clearly higher than conventionally believed. (C) 2000 by Elsevier Sc ience Inc. All rights reserved.