A novel constitutional mutation affecting splicing of retinoblastoma tumor suppressor gene intron 23 causes partial loss of pRB activity.

Hereditary predisposition to retinoblastoma is caused by germ line mutations in the RB1 gene. Genetic counseling of affected individuals and accurate risk prediction for their families requires identification of the disease causing mutation. Furthermore, the nature of a mutation can determine genetic penetrance, disease presentation and prognosis. We describe, and functionally characterize here, a novel mutant allele of RB1 present in the germ line of a patient with sporadic bilateral retinoblastoma. The mutation generates an operational splice acceptor site resulting in a predicted protein product with loss of 81 amino acids from its carboxy terminus. We demonstrate that the aberrantly spliced transcript is present in substantial amounts in peripheral blood of the patient and present evidence that the predicted protein product displays partial loss of activity reflecting in degree and presentation that of the partially penetrant RB1 missense mutant R661W. This infers that disease with reduced expressivity and incomplete penetrance may arise in individuals that carry the mutation and predicts such presentation for similar mutations with found in sporadic cases in the past.