A genetic view of the Samaritan isolate

Abstract

Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at [email protected]. Thank you.The Samaritan community in the Middle East is the solitary heir of a continuous religious and cultural tradition, probably going back to an early stage in Biblical history. From a national unit of several thousand souls they have gradually become a small sect of only a few hundred individuals. There are today a total of about 381 Samaritans divided into two groups that live under different political allegancies, Jordan and Israel, but in the same geographical area that they have never left for a period of more than 2000 years. There are about 225 Samaritans residing in Nablus, Jordan, and 156 in Cholon (near Tel-Aviv) Israel. Once a year, at their Passover, all the members of the two communities join in a pilgrimage to Mt. Gerizim, near the city of Nablus. A genetic and anthropological survey of the Samaritan community in Israel carried out in the autumn of 1963 included tests for about 30 blood group antigens, several serum proteins, hemoglobin variants, Glucose-6-Phosphate Dehydrogenase activity, secretor status, color-blindness and some 18 anthropometric measurements and 18 morphological observations. About 90% of the total group were studied. All typings of red cell antigens, G6PD and hemoglobin variants were performed by conventional methods at the Tel Hashomer Hospital in Israel. Sera specimens were frozen and shipped to the U.S.A. and were tested for the following plasma components: 1. Haptoglobins and transferrins (by starch-gel electrophoresis) 2. Groups Specific Component (Gc types, by immunoelectrophoresis) 3. Lipoproteins (by the Ouchterlony procedure) 4. Gamma Globulins and Inv (a) factors by the methods used in Steinberg's Laboratory at Western Reserve University, Cleveland, Ohio. The tests for PTC taste sensitivity followed the sorting technique of Harris and Kalmus, and deficiency in color-vision was detected by the Ishihara charts and the Pickford-Nicolson anomaloscope. The anthropometry procedures followed the standard techniques of Martin. The results obtained show that the Samaritans possess a characteristic gene frequency picture which does not resemble that of any other community in the same region; in blood groups they have the highest 0 frequency in the Middle East; A2 is more common than A1 and the N gene is more frequent than M. Not a single case of G6PD deficiency was found. The incidence of color-blindness is very high (27%). There is heterogeneity in physical type and large variations between individuals are also manifested in hair and eye-color distribution. Comparison of gene frequencies within the isolate as observed in 1933 and in 1963 as well as in an age-group analysis shows that the differences between generations are very small and below magnitude that might be expected on the basis of random genetic drift. The genetic diversity of the community suggests that is spite of their being genetically isolated for a very long time no genes have been "fixed" or "lost" although the statistical probability for such an occurrence is high. This fact, and the apparent state of equilibrium in most of their genetic systems suggests that compensating selecting forces are acting to stabilize the gene frequencies. It seems likely that the isolate has developed its own unique integrated polygenic system, one that tends to persist. Examination of the degree of consanguinity in the population indicates that in 84% of the matings the partners are first cousins or second cousins. The mean coefficient of inbreeding (as computed by an IBM 1620 computer) for the present generation is 0.069: the highest value recorded for any human community. The inbred nature of this small isolate, however, is not reflected in an excess of homozygotes nor in a high incidence of congenital malformations and abnormalities. Also, sterility, abortions and infant mortality were not proportional to the degree of inbreeding. Lack of evidence for specific deleterious effects in the Samaritans leads to the suggestion that inbreeding has been practiced in this isolate for such a long time that the population has "purged" itself of many of its detrimental genes.2031-01-0