In medical genetics, the information given by the patient and his/her family is often a clue to diagnosis. One important piece of information is whether the parents of the patient are consanguineous. In most western societies, consanguineous marriages are rare, and this information is usually well known; however, this is not always the case in inbred populations.
We recently completed a study on the prevalence of genetic disorders in a Muslim Arab village of 8,600 inhabitants. We collected data on married couples by personal interviews, mostly of both spouses, including details about health problems, the number of children, and the existence and the type of relationship between the spouses. In addition, each individual interviewed gave us details on the existence and the type of relationship between his parents. The couples were divided into two groups, according to the way the information was obtained: directly, by at least one member of the couple, or indirectly, by at least one of the children of the couple. In 77 of the 331 couples interviewed, the spouses were first cousins (23.2%), whereas, among the 256 couples on whom we obtained the information indirectly, 29 of the spouses were first cousins (11.3%). The rate of first-cousin marriages in the couples from whom we obtained the information directly was similar in range to that obtained in the rural Arab population [Freundlich and Hino, 1984;Jaber et al., 1994]. However, there was a very significant difference in the percentages of first-cousin marriages between the couples from whom information was obtained directly and the couples on whom information was obtained indirectly ( 2 ס 20.1; P < 0.005). The couples were from the same background, and the main difference between the groups studied was the age of the spouses. The couples interviewed by us were of various ages, including those that were newly married, whereas those from whom the data were obtained indirectly had at least one adult married child, who gave us the information; in general, these couples were older. Thus, the significantly higher percentage of first-cousin marriages in the first group