Regarding retinoblastoma all of the following are true, EXCEPT:

Hereditary retinoblastoma accounts for 40% of cases. All bilateral and cases and about 15% of the unilateral cases are hereditary. Retinoblastoma gene has been identified as 14 band on the long-arm of chromosome 13 (13q14). Deletion or inactivation of this protective gene by two mutations results in occurrence of retinoblastoma. Inheritance is autosomal dominant and the risk of transmitting the gene mutation is 50%. Because of high penetrance 40% of offspring of a surviver of hereditary retinoblastoma will develop the tumor. 33% are bilateral (1/3rd cases). Ref: Ophthalmology by A K Khurana 4th edition, Page 280