Human genetics: past, present, and future, with special reference to major trends in Japan

Fifty years of genetic epidemiology, with special reference to Japan

Genetic epidemiology deals with etiology, distribution, and control of disease in groups of relatives and with inherited causes of disease in populations. It took its first steps before its recognition as a discipline, and did not reach its present scope until the Human Genome Project succeeded. The intimate relationship between genetics and epidemiology was discussed by Neel and Schull (1954), just a year after Watson and Crick reported the DNA double helix, and 2 years before human cytogenetics and the Japan Society of Human Genetics were founded. It is convenient to divide the next half-century into three phases. The first of these (1956-1979) was before DNA polymorphisms were typed, and so the focus was on segregation and linkage of major genes, cytogenetics, population studies, and biochemical genetics. The next phase (1980-2001) progressively identified DNA polymorphisms and their application to complex inheritance. The last phase began with a reliable sequence of the human genome (2002), followed by exploration of genomic diversity. Linkage continues to be useful to study recombination and to map major genes, but association mapping gives much greater resolution and enables studies of complex inheritance. The generation now entering human genetics will have collaborative opportunities undreamed of a few years ago, without the independence that led to great advances during the past half-century.

Allelic loss on chromosome 9q is associated with lymph node metastasis of primary breast cancer

Frequent allelic losses on chromosome 9 are seen in a wide variety of human tumors; moreover, two genes (P16 and PTC) whose mutant alleles confer predispositions to some inherited cancer syndromes have been identified on this chromosome. Using 15 highly polymorphic microsatellite markers distributed on both arms of chromosome 9, we tested 96 primary breast carcinomas for allelic loss in order to define the locations of genes that might be involved in this type of tumor. Allelic loss was observed in 37 of the tumors (39%) and detailed deletion mapping identified target regions at 9p21, 9q22.3 and 9q33. Losses at 9q22.3 and 9q33 were correlated with the presence of lymph node metastasis, and allelic loss at 9q22.3 was observed more frequently in scirrhous tumors than in less aggressive histologic types. Therefore, inactivation of tumor suppressor genes in 9q22.3 and 9q33 regions might play a role in progression of breast cancers, especially in metastasis to lymph nodes and in development of scirrhous tumors.

Somatic mutations of the PTEN/MMAC1 gene in fifteen Japanese endometrial cancers: evidence for inactivation of both alleles

Loss of heterozygosity (LOH) of chromosome 10q is observed in approximately 40% of endometrial cancers. Mutations in PTEN/MMAC1, a gene recently isolated from the 10q23 region, are responsible for two dominantly inherited neoplastic syndromes, Cowden disease and Bannayan-Zonana syndrome. Somatic mutations of this gene have also been detected in sporadic cancers of the brain, prostate and breast. To investigate the potential role of this putative tumor suppressor gene in endometrial carcinogenesis as well, we examined 46 primary endometrial cancers for LOH at the 10q23 region, and for mutations in the entire coding region and exon-intron boundaries of the PTEN/MMAC1 gene. LOH was identified in half of the 38 informative cases, and subtle somatic mutations were detected in 15 tumors (33%). Our results suggest that of the genes studied so far in endometrial carcinomas, PTEN/MMAC1 is the most commonly mutated one, and that inactivation of both copies by allelic loss and/or mutation, a pattern that defines genes as "tumor suppressors," contributes to tumorigenesis in endometrial cancers.