DNA methylation has recently moved to centre stage in the aetiology of human neurodevelopmental syndromes such as the fragile X, ICF and Rett syndromes. These diseases result from the misregulation of genes that occurs with the loss of appropriate epigenetic controls during neuronal development. Recent advances have connected DNA methylation to chromatin-remodelling enzymes, and understanding this link will be central to the design of new therapeutic tools.

DNA methylation in health and disease

Identification of a deletion in plakoglobin in arrhythmogenic right ventricular cardiomyopathy with palmoplantar keratoderma and woolly hair (Naxos disease).

The discovery of the first gene associated with hereditary breast cancer, BRCA1, was anticipated to greatly increase our understanding of both hereditary and sporadic forms of breast cancer, and to lead to therapeutic and preventive breakthroughs. Much has been learned during the past decade about the genetic epidemiology of breast cancer, the ethnic distribution and clinical consequences of BRCA1 and BRCA2 mutations, and the central role of DNA repair in breast cancer susceptibility. The ability to translate this knowledge into novel treatments, however, remains elusive.

BRCA1 and BRCA2 : 1994 and beyond

Objectives. —To identify predictors of utilization of breast-ovarian cancer susceptibility ( BRCA1 gene) testing and to evaluate outcomes of participation in a testing program. Design. —Prospective cohort study with baseline interview assessment of predictor variables (eg, sociodemographic factors, knowledge about hereditary cancer and genetic testing, perceptions of testing benefits, limitations, and risks). BRCA1 test results were offered after an education and counseling session in a research setting. Outcome variables (including depression, functional health status, and prophylactic surgery plans [follow-up only]) were assessed at baseline and 1-month follow-up interviews. Participants. —Adult male and female members (n=279) of families with BRCA 1 -linked hereditary breast-ovarian cancer (HBOC). Results. —Of subjects who completed a baseline interview (n=192), 60% requested BRCA 1 test results (43% of all study subjects requested results). Requests for results were more frequent for persons with health insurance (odds ratio [OR], 3.74; 95% confidence interval [CI], 2.06-6.80); more first-degree relatives affected with breast cancer (OR, 1.59; 95% CI, 1.16-2.16); more knowledge about BRCA1 testing (OR, 1.85; 95% CI, 1.36-2.50); and indicating that test benefits are important (OR, 1.45; 95% CI, 1.13-1.86). At follow-up, noncarriers of BRCA1 mutations showed statistically significant reductions in depressive symptoms and functional impairment compared with carriers and nontested individuals. Individuals identified as mutation carriers did not exhibit increases in depression and functional impairment. Among unaffected women with no prior prophylactic surgery, 17% of carriers (2/12) intended to have mastectomies and 33% (4/12) to have oophorectomies. Conclusions. —Only a subset of HBOC family members are likely to request BRCA 1 testing when available. Rates of test use may be higher in persons of a higher socioeconomic status and those with more relatives affected with breast cancer. For some high-risk individuals who receive test results in a research setting that includes counseling, there may be psychological benefits. More research is needed to assess the generalizability of these results and evaluate the long-term consequences of BRCA1 testing. ( JAMA . 1996;275:1885-1892)

https://jamanetwork.com/journals/JAMA/articlepdf/404205/jama_275_24_036.pdf

BRCA1 testing in families with hereditary breast-ovarian cancer. A prospective study of patient decision making and outcomes.

The field of epigenetics has recently moved to the forefront of studies relating to diverse processes such as transcriptional regulation, chromatin structure, genome integrity, and tumorigenesis. Recent work has revealed how DNA methylation and chromatin structure are linked at the molecular level and how methylation anomalies play a direct causal role in tumorigenesis and genetic disease. Much new information has also come to light regarding the cellular methylation machinery, known as the DNA methyltransferases, in terms of their roles in mammalian development and the types of proteins they are known to interact with. This information has forced a new view for the role of DNA methyltransferases. Rather than enzymes that act in isolation to copy methylation patterns after replication, the types of interactions discovered thus far indicate that DNA methyltransferases may be components of larger complexes actively involved in transcriptional control and chromatin structure modulation. These new findings will likely enhance our understanding of the myriad roles of DNA methylation in disease as well as point the way to novel therapies to prevent or repair these defects.

DNA methylation, methyltransferases, and cancer.

Although more than 100 different BRCA1 germ-line mutations have already been identified in breast and/or ovarian cancer families, we report for the first time a deleterious genomic rearrangement in BRCA1. A 1-kb deletion comprising exon 17 was found in a large breast and ovarian cancer family, leading to a frameshift in the mutant mRNA due to the absence of exon 17. This deletion is probably the result of a recombination between two closely related Alu sequences. It was not detected by conventional PCR-based methods involving the genomic screening of the 22 coding exons or reverse transcription-PCR because the transcript without exon 17 is unstable in lymphoblastoid cell lines. Therefore, rearrangements in the BRCA1 gene should be sought in breast/ovarian cancer families in which no mutations have been found by PCR-based methods in the coding region or in the splice sites.

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A 1-kb Alu-mediated germ-line deletion removing BRCA1 exon 17.

We have analyzed 20 breast-ovarian cancer families, the majority of which show positive evidence of linkage to chromosome 17q12 for germ-line mutations in the BRCA1 gene. BRCA1 mutations cosegregating with breast and ovarian cancer susceptibility were identified in 16 families, including 1 family with a case of male breast cancer. Nine of these mutations have not been reported previously. The majority of mutations were found to generate a premature stop codon leading to the formation of a truncated BRCA1 protein of 2%-88% of the expected normal length. Two mutations altered the RING finger domain. Sequencing of genomic DNA led to the identification of a mutation in the coding region of BRCA1 in 12 families, and cDNA analysis revealed an abnormal or missing BRCA1 transcript in 4 of the 8 remaining families. A total of eight mutations were associated with a reduced quantity of BRCA1 transcript. We were unable to detect BRCA1 mutations in 4 of the 20 families, but only 1 of these was clearly linked to BRCA1. It is expected that the majority of clear examples of the breast-ovarian syndrome will be associated with germ-line mutations in the coding region of BRCA1.

A high incidence of BRCA1 mutations in 20 breast-ovarian cancer families.

The gene encoding human plakoglobin was mapped to chromosome 17q12-q22. An intragenic restriction fragment length polymorphism was used to localize the plakoglobin gene distal to locus KRT10 and proximal to the marker D17S858. The plakoglobin gene colocalizes with the polymorphic 17q21 marker UM8 on the same cosmid insert. This subregion of chromosome 17 is known to be particularly subjected to genetic alterations in sporadic breast and ovarian tumors. We show loss of heterozygosity of the plakoglobin gene in breast and ovarian tumors. We have identified a low-frequency polymorphism in the plakoglobin coding sequence which results in an arginine to histidine substitution at amino acid position 142 of the protein, as well as a silent mutation at nucleotide position 332 of the coding sequence. This polymorphism allowed us to demonstrate an allelic association of plakoglobin with predisposition to familial breast and ovarian cancers. Our results, together with the present knowledge about the biological function of plakoglobin, suggest that plakoglobin might represent a putative tumor suppressor gene for breast and ovarian cancers.

Delphine Torchard

Papers

A 1-kb Alu-mediated germ-line deletion removing BRCA1 exon 17.

A high incidence of BRCA1 mutations in 20 breast-ovarian cancer families.

The human plakoglobin gene localizes on chromosome 17q21 and is subjected to loss of heterozygosity in breast and ovarian cancers