Phenotype

Retinoblastoma occurs in one eye or both eyes.
An important early sign is the so-called “cat’s
eye,” awhite shimmer out of the affected eye (1)
or the development of strabismus. One or
several tumors originate from the retina (2).
The tumor progresses rapidly (3). The relative
proportions of the genetic types of retinoblastoma
are about 60% somatic mutations (nonhereditary
form) and 40% germline mutations,
transmitted as an autosomal dominant trait
(hereditary form, in about 10–15%, due to
transmission from a parent; the remainder due
to a new mutation). New mutations usually affect
a paternal allele (about 10: 1). In about 10%
of carriers of a germline mutation no tumor
develops (nonpenetrance).