RB1 germ-line deletions in Argentine retinoblastoma patients.
BACKGROUND
Retinoblastoma (RB) is a malignant tumor originating in the retinal cell precursors and can be presented as a unilateral or bilateral form in childhood (one or both eyes affected). Development of this tumor is caused by mutations in the RB1 gene on chromosome 13q14; the first mutation may occur in the germ line (hereditary RB) or in somatic cells (non-hereditary RB). The hereditary form of RB is transmitted with a high penetrance to offspring (90%). Because early diagnosis is necessary for implementing effective treatment and preserving vision, it is important to identify the mutations in the affected family.


OBJECTIVE
The aim of this study was to identify large and small RB1 germ-line mutations and to correlate them with the RB phenotype.


METHODS
Constitutional RB1 gene gross deletions were studied in 40 patients with bilateral or unilateral familial RB by a segregation assay of four intragenic polymorphisms located in introns 1, 4, 17, and 20 of the RB1 gene, along with fluorescence in situ hibridization (FISH) analysis. Small mutations were ascertained in a subgroup of ten patients by heteroduplex/sequence analysis of RB1-exons.


RESULTS
In the course of our study, we have found three large deletions, which probably represent whole gene deletions, and two small deletions of 1bp in length. One large deletion was found in a family with several members affected. This represents a rare case of familial RB, which is usually caused by small mutations. Phenotype analysis of the family revealed a low penetrance inheritance, with an 'affected eyes : number of mutation-carriers' ratio of approximately 1.0, whereas this ratio in families with small loss-of-function mutations is 1.5-2.0.


CONCLUSIONS
Our results emphasize the usefulness of a combined methodology that includes segregation of polymorphisms, FISH, and heteroduplex/sequence analyses for detection of gross and small DNA rearrangements in familial and sporadic RB. Identification of mutations in sporadic cases is important for risk-assessment in patients' relatives. The degree of penetrance in the inheritance of RB not only depends on the occurrence of the second mutation in the RB1 gene but also on the extent of inactivation of the first mutation.
Fernández
Cecilia
C
Genetics and Molecular Biology Department, Faculty of Pharmacy, Jose de San Martin Hospital, Buenos Aires University, Buenos Aires, Argentina.
Repetto
Karina
K
Dalamon
Viviana
V
Bergonzi
Fenanda
F
Ferreiro
Veronica
V
Szijan
Irene
I
D001118:Argentina; D002882:Chromosomes, Human, Pair 13; D005091:Exons; D005134:Eye Neoplasms / Q000235:genetics*; D007839:Functional Laterality; D017353:Gene Deletion; D018095:Germ-Line Mutation; D006801:Humans; D018598:Minisatellite Repeats; D012175:Retinoblastoma / Q000235:genetics*; D016160:Retinoblastoma Protein / Q000235:genetics*
D016160:Retinoblastoma Protein