Siblings of retinoblastoma patients: Are we underestimating their risk?

PURPOSE: To describe the clinical presentation of probable germ-line mosaicism 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 identify those with potential germ-line mosaicism. Parents and siblings of retinoblastoma patients were given comprehensive ophthalmologic examinations. RESULTS: Four kindreds were identified, wherein retinoblastoma was diagnosed in two siblings and both parents demonstrated no evidence of retinoblastoma or retinocytoma. CONCLUSION: Clinical appearance of germ-line mosaicism is demonstrated in our retinoblascoma patient populations. We recommend routine clinical screening 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 considered as a genetic transmission pattern in these patients, and genetic counseling should specifically recognize this possibility. If a parent is germ-line mosaic, the possibility of bearing a second child with retinoblastoma is clearly higher than conventionally believed. (C) 2000 by Elsevier Science Inc. All rights reserved.