Oncogenic point mutations in the human retinoblastoma gene: their application to genetic counseling

Article Abstract:

Retinoblastoma is a cancer of the retina, the portion of the eye that receives images and transmits them to the brain through nerve impulses. There are hereditary and nonhereditary forms of the cancer, with 40 percent of the cases being hereditary. However, only one quarter of the hereditary cases have a family history of retinoblastoma. Three quarters of the cases are caused by mutations in the germ cells, the developing egg or sperm of the individual, from which all the cells of the body are derived. Patients with the hereditary form of the cancer can pass the disease to their offspring, which occurs in 90 percent of the cases. Because the inheritance of the disease is not straightforward and survival is greatly increased if treatment occurs early, there is a need for early diagnosis of the disease. The DNA (deoxyribose nucleic acid) which codes for the gene responsible for the disease has been identified and characterized. Using molecular biological techniques that are very sensitive, mutations or abnormal changes were found in the DNA of the retinoblastoma gene in tumors from seven patients who had no family history of retinoblastoma. If the changes appearing in the DNA from the tumor cells also occurred in other, nontumorous cells, it is posited that the mutations must have occurred in the patients' germ cells, and thus could be passed on to their offspring. If the changes occurred only in the tumor cells and not in other cells, the disease would not be inheritable. Thus heritable and noninheritable forms of retinoblastoma can be distinguished. This information is important for genetic counseling regarding the risks of transmittance of the disease to offspring.

Research, Genetic screening, Genetic testing, Molecular biology, Retinoblastoma

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Mutations within the rhodopsin gene in patients with autosomal dominant retinitis pigmentosa

Article Abstract:

Retinitis pigmentosa, a hereditary and degenerative eye disease, affects as many as 100,000 people in the US. An early sign of the disease is night blindness, which progresses to total blindness in most cases by late adulthood. To learn more regarding the genetic control of this condition, investigators analyzed a segment of chromosome 3 known to be linked to the disease trait in one family. This is also the same gene that controls production of rhodopsin, the visual pigment essential for night vision. Blood samples were obtained from 150 patients with a family history of retinitis pigmentosa, which had been passed on in an autosomal dominant manner, and analysis of the rhodopsin gene was performed on white blood cells; 106 normal control subjects were also tested. Three mutations were found; their locations are described. Codon 23, which was discovered in an earlier study, along with codons 58 and 347, are three mutations now known to be involved in retinitis pigmentosa; 18 percent of the 150 patients had one of these defects. Additional genetic techniques revealed that at least one of the mutations (that on codon 23) had probably originated in a common ancestor. One of the codon 347 mutations probably arose independently in at least two ancestors. Knowledge regarding these mutations can make blood screening available for members of families with retinitis pigmentosa to determine if they carry the defective gene. (Consumer Summary produced by Reliance Medical Information, Inc.)

Methods, Testing, Medical screening, Health screening, Retinitis pigmentosa

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Prevalence and spectrum of germline mutations of the p53 gene among patients with sarcoma

Article Abstract:

Germline mutations in the tumor-suppressor gene p53 may be common among sarcoma patients who have a personal or family history of cancer, but not among those who do not. Of 196 sarcoma patients whose DNA was analyzed, eight germline mutations in the p53 gene were found. Five mutations were found in patients who had had multiple types of cancer or with a known family history of cancer. Three mutations were found in patients with no personal or known family history of cancer. Two of these mutations were considered to be new with the patient. Four mutations changed the amino acid composition of the protein for which the gene encodes, and four resulted in an abrupt termination of protein synthesis. None of these mutations were found among 200 healthy individuals. Individuals who have inherited mutations in tumor-suppressor genes may be more likely to develop cancer than other individuals. Identification of these mutations allows for genetic counseling of individuals who have inherited them.

Health aspects, Tumor suppressor genes, Sarcoma

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