Mutations in the BRCA1 gene in families with early-onset breast and ovarian cancer.

We analysed 50 probands with a family history of breast and/or ovarian cancer for germline mutations in the coding region of the BRCA1 candidate gene, using single-strand conformation polymorphism (SSCP) analysis on PCR-amplified genomic DNA. A total of eight putative disease-causing alterations were identified: four of these are frameshifts and two are nonsense mutations. In addition, we found two missense mutations, one of which changes the final cysteine of the BRCA1 zinc finger motif to glycine. These data are consistent with a tumour suppressor model, and support the notion that this candidate gene is in fact BRCA1. The heterogeneity of mutations, coupled with the large size of the gene, indicates that clinical application of BRCA1 mutation testing will be technically challenging.

Precise gene dosage determination by polymerase chain reaction: theory, methodology, and statistical approach.

We developed a general method of quantifying relative copy numbers of specific DNA sequences based on the theoretical accumulation of polymerase chain reaction (PCR) products when two DNA sequences are amplified together (co-amplified). Our experiments illustrate the development and theory of the technique. The precision of our estimates is demonstrated by statistical confidence intervals. Tests for effects introduced by experimental factors were performed. The precision of the technique was established by examining the relative gene dosage of the X-linked dystrophin gene in human genomic DNAs from a male, a normal female, a 47,XXX female, and a 48,XXXX cell line. The sensitivity was sufficient to distinguish three copies of the gene from four copies; equivalent to detecting loss of heterozygosity in half the cells of a tumour. Confidence intervals allowed us to reject the hypothesis that there was no difference between DNA samples. Four sample pairs would be required to demonstrate relative gene dosage ratios of 2.0 to 1.0; eight sample pairs would be required to demonstrate a relative gene dosage ratio of 1.3 to 1.0. This method should be useful in detecting gene amplification and deletion in a variety of situations.

Genetics of common diseases of adulthood. Implications for prenatal counseling and diagnosis.

Genetic factors play an important role in the development of many common diseases of adulthood that result in early morbidity and mortality. Prevention of these disorders and their sequelae is best established through early detection and early intervention. Although it may be feasible to screen the entire population for some disorders (e.g., hypertension), this approach would be expensive and impractical for others (e.g., colon cancer). The family history provides an inexpensive and convenient method of identifying families at risk for premature diseases of adulthood. Family screening for a disorder should be recommended if there is increased risk for the disorder among family members, if screening methods are available to detect the condition at an early age or preclinical stage, and if early intervention will alter the course of the disease. For many disorders screening and intervention can prevent the occurrence of clinical disease. The prenatal counseling session affords an ideal setting for identifying families at risk for diseases of adulthood with major genetic components. By reviewing the family history, key family members can be identified and investigated, in order to establish a specific genetic diagnosis. At-risk relatives can then be counseled and screened for the disorder preclinically and premorbidly. The screening and intervention available for a disease depends on the nature of the disorder, our understanding of its physiology and etiology, and our current technology. The disorders discussed earlier are typical of conditions of adulthood that are influenced strongly by genetic factors, especially when they appear in younger adults. Atherosclerosis, colon cancer, and diabetes are complex phenotypes. Each can be caused by single-gene defects, but commonly the genetics are more complex. Empiric data help to establish the risk to an individual in the latter cases. In all three examples, early detection should lead to treatment, which can prevent more serious sequelae: by treating the dyslipidemia, coronary artery disease can be prevented; by removing the benign polyp, malignant cancer can be avoided; and when impaired glucose tolerance is detected, diet and exercise can prevent or delay frank diabetes and its complications. The complete evaluation of individuals at risk for disorders such as those in Table 1 and their families can be a complicated task. Referral to a center experienced in the genetics of common diseases often may be necessary.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytogenetic characterization of renal cell carcinoma in von Hippel-Lindau syndrome.

We report the case of a 26-year-old man with von Hippel-Lindau syndrome (VHL) and two renal cell carcinomas (RCC), one of which was studied cytogenetically. Chromosomal analysis of the RCC showed a translocation that involved chromosomes 3 and 8 with subsequent loss of the derivative chromosome 8. The patient's peripheral lymphocytes showed a normal karyotype that indicated that there was not a constitutional chromosomal translocation. This is the third reported case of RCC in a patient with VHL in which loss of a portion of the short arm of chromosome 3 (3p) has occurred. Similar chromosomal changes that involve 3p have been reported in both familial and sporadic cases of RCC and have led to speculation that a tumor suppressor gene may be located in this region. Cytogenetic characterization of renal tumors could assume increasing significance in the diagnosis and classification of RCC and potentially may guide therapy. These studies may also lead to a better understanding of the biologic behavior of RCC and result in more informed patient evaluation and counseling.