ABSTRACT
BACKGROUND: Retinoblastoma is a neuroblastic tumor of childhood with an incidence of 1: 20 000. Retinoblastoma gene (Rb1) is a tumor suppressor gene that is located on the long arm of chromosome 13 at region 14. This study was to evaluate the constitutional monoallelic Rb1 deletion among retinoblastoma families. METHODS: Nine families with an affected Rb proband were evaluated. Clinical examination, pedigree analysis, and complete eye examination were given to patients, their sibs and parents. Standard cytogenetic and fluorescence in situ hybridization (FISH) analyses were carried out for all of them. Also, two sib fetuses were tested for Rb1 deletion. RESULTS: No dysmorphic features were detected in any patient. Developmental milestones were within normal limit except in one proband who had a mild delay. The age of onset ranged from one month to 4 years. Positive family history was found in two families. In one, the father and 3 sibs had retinoblastoma, and in the other, 2 sibs were affected, but the parents were free. Chromosomal study revealed no abnormalities in all parents and sibs. Two patients had mosaic chromosome 13 abnormalities, 46,XY/46,XY,del(13)(pter-->q14:) and 46,XX/46,inv(13)(q14q22). FISH analysis detected mosaic Rb1 deletion in two patients and excluded Rb1 deletion in two fetuses. CONCLUSIONS: The detection of genetic alterations affecting the Rb1 locus is important for the establishment of carriers, and prenatal and presymptomatic diagnosis. The search for deleted Rb1 mosaic cell lines is important for genetic counseling. Germline mutation may be considered as genetic transmission method of the Rb1 gene.