E: Retinoblastoma
When a light is shone on the eye (eg. camera flash), the pupil appears red. This is called the pupillary red reflex.
Leukocoria is an abnormal pupillary white reflex. It is caused by many conditions, including congenital cataract and retinoblastoma.
In this case, the family historu of enucleation (removal of eye) makes retinoblastoma the more likely diagnosis. This is because enucleation is a treatment option for retinoblastoma but not congenital cataracts.
Retinoblastoma is caused by mutations of the RB1 tumour suppressor gene. Given that a grandparent also had retinoblastoma, it is likely that they passed on 1 mutated RB1 gene to the granddaughter’s parent. This carrier parent then passed on that mutated RB1 gene to their daughter. At some point thereafter, she acquired a sporadic mutation of her normal RB1 allele, resulting in retinoblastoma of that eye.