Oncogenic Point Mutations in the Human Retinoblastoma Gene: Their Application to Genetic Counseling

TLDR

Mutations in the retinoblastoma gene, often undetectable by Southern blotting, underlie both hereditary and nonhereditary retinoblastoma and predispose to other cancers, with germ‑cell mutations conferring risk for additional tumors and transmission to offspring. The authors employed primer‑directed enzymatic amplification followed by DNA sequencing to detect single‑nucleotide changes in tumors from seven simplex retinoblastoma patients. The method revealed that four patients had tumor‑specific mutations, three had new germ‑cell mutations absent in parents, and point mutations were also identified in bladder, lung, and another retinoblastoma, demonstrating the technique’s ability to differentiate hereditary from nonhereditary disease and aid risk assessment and counseling.

Abstract

Mutations of the retinoblastoma gene, most of which cannot be detected by conventional Southern blotting, are known to cause both the nonhereditary and hereditary forms of retinoblastoma and have been implicated in the development of other cancers. Nonhereditary retinoblastoma is caused by a somatic mutation. Hereditary retinoblastoma is caused by a germ-cell mutation, most often a new one, and thus there is usually no family history of the disease. Unlike patients with the nonhereditary disease, those with the hereditary form are at risk for additional retinoblastomas, and their progeny are at risk for the tumors. We used a sensitive technique of primer-directed enzymatic amplification, followed by DNA sequence analysis, to identify mutations as small as a single nucleotide change in tumors from seven patients with simplex retinoblastoma (with no family history of the disease). In four patients the mutation involved only the tumor cells, and in three it involved normal somatic cells as well as tumor cells but was not found in either parent; thus, these mutations appeared to be new, germ-cell mutations. In addition, we found point mutations in cells from a bladder carcinoma, a small-cell carcinoma of the lung, and another retinoblastoma. We conclude that the technique that we have described can distinguish hereditary from nonhereditary retinoblastoma and that it is useful in risk estimation and genetic counseling.