RB1 and retinoblastoma: However, 45% of all reported cases encompass the heritable form of retinoblastoma, a biallelic germline mutation of the retinoblastoma tumor suppressor gene RB1. [1] In 80% of children with heritable disease, retinoblastoma affects both eyes (bilateral) and 5% of the cases are associated with an intracranial tumor (trilateral).