What is the California Twin Program?

The California Twin Program at the University of Southern California School of Medicine was begun in 1992, and is directed by Thomas Mack, M.D., a Professor in the Department of Preventive Medicine. All 265,000 twins born in California between 1908 and 1982 are eligible for enrollment in the Program. We have succeeded in locating approximately 150,000 individuals now living in and out of the state.
As resources are made available, twins will be asked to check answers to a set of questions which address occupation and education, lifestyle (including diet and exercise habits), family structure, personal and family history of disease. The general goals of the program are to describe the characteristics of native California twins, as themselves and as representatives of all native Californians. The more specific goal is to permit the identification of twins with special characteristics who might be willing to participate in the study of specific medical problems.

Progress We've Made

 Our first questionnaire was sent to twins who in 1992 were over the age of 37 (at that time) and for whom we had an address. We received approximately 20,000 responses, a majority of those who were sent the questionnaire. Some of the general information provided by these responses is described under results. Some very important studies are being conducted with small groups of twins chosen from among these 20,000. We are trying to learn whether or not the characteristics of normal mammograms provide any hint of risk from breast cancer, and if so if such a hint is inherited or acquired.
We are continuing ongoing studies of twins with early-onset diabetes, with psoriasis, and with rheumatoid arthritis. Healthy identical female twins have been selected for a study of the reasons why there are differences in the level of blood estrogens, an important risk factor for breast cancer. Twins who differ in their history of smoking are helping us to learn about the long-term effects of smoking on the function of the lymphocytes, the white cells in the blood. We have now received support for the purpose of enrolling a large set of slightly younger twins, those over about 30. Letters of introduction, along with a decal displaying the twin bear logo, have been put in the mail.