Study of 15 protein polymorphisms in a sample of the Turkish population

A. BREGA, R. SCACCHI,2 M. CUCCIA,3 B. KIRDAR, G. PELOSO, AND R.M. CORBO '

KEY WORDS: TURKISH POPULATION, PROTEIN POLYMORPHISMS, MULTIVARIATE ANALYSIS

Abstract Anatolia, because of its geographic position and its use as an area of settlement, was also a land of transit that accommodated a succession of populations. The last important invasion occurred in the Middle Ages with the arrival of the Turks, an Altaic-speaking nomadic population descended from the Oguz tribes and originating in Mongolia. Although the Turks imposed their culture, their genetic contribution seems to have been modest. To validate this hypothesis, we studied the genetic structure of the Turkish population by examining 15 genetic markers in a sample of 93 subjects. The allele frequencies observed were HP = 0.240; GLO]*l = 0.344, ESD*2 = 0.134, GC*IS = 0.613, GC*IF = 0.129, PGMI*2S = 0.322, PGMI*2F = 0.041, PGMIF = 0.027, F13B*1 = 0.762, F13B*2 = 0.101, ORMI *S = 0.327, AHSG*2 = 0.181, C6*B = 0.239, C7*1 = 0.983, APOC2*1 = 1.0, APOE*3 = 0.868, APOE*2 = 0.063, BF*F = 0.258, BF*S07 = 0.017, BF*SQO = 0.011, C4A*QO = 0.145, C4A*2 = 0.070, C4A*5 = 0.012, C4A*6 = 0.023, C4B*QO = 0.101, C4B*2 = 0.048, C4B*3 = 0.005, and C4B*11 = 0.005. The present Turkish population was compared to other European, Middle Eastern, and North African populations by means of correspondence analysis. Turks cluster with Turkomans, who share the ancient Turks' derivation from the Oguz tribe. Moreover, Turks clearly belong to European groups and resemble the populations of neighboring countries. Therefore the present data support the hypothesis that the ancient Turkish tribes, who started to enter Anatolia 1000 years ago, contributed little to the gene pool of the preexisting Anatolian populations. Alternatively, if the genetic structure of the invading Turks resembled that of the ancient Anatolians, it will be impossible to find traces of their admixture with the autochthonous inhabitants of Anatolia. However, further analysis of other samples from Turkey and from populations living in the homelands of the Turkish tribes, namely, the eastern area of the Caspian Sea and Mongolia, is needed.

Because of its geographic position and high-plain physical conformation, Anatolia must have been, even in nonhistorical ages, not only a place of permanent settlement but also a land of transit for nomadic populations migrating toward Europe, regions of western Asia, and North Africa. Anatolia has been inhabited since the Paleolithic, as evidenced by archeological records found near Adalia (Karain cavern). Toward the end of the Bronze Age (4000 years B.P.), with the arrival of the Hittite Indo-European population, Anatolia entered the historical age. Thereafter, the area underwent a succession of dominations by differing populations: Phrygians, Acheans, Cimners, Assyrians, Lydians, Persians, Macedonians, and Romans. During the Middle Ages, Anatolia experienced its last important invasion: the Turks, who entered the region in repeated waves.

The Turks were nomadic Altaic-speaking populations who originated in Mongolia; as descendants of the T'u-chueh (a Chinese name later transformed to Turk) tribe, the Turks were ethnically distinct from the Mongols. Turkish groups who descended from the Oguz tribes and who mixed with nomadic and indigenous settled populations invaded Anatolia in the twelfth century A.D. and were the definitive conquerors of its capital, Constantinople (A.D. 1453), now Istanbul. The Turkish newcomers were able to impose their culture and language through an elite dominance process (Renfrew 1987, pp. 131-133) but seem to have imparted only a modest genetic contribution (Cavalli-Sforza et al. 1994, pp. 202, 245, and 299), as shown by the scanty existing data (Caglagan et al. 1995; Alper, Meyer et al. 1995; Alper, Wiegand et al. 1995; Calafell et al. 1996; Comas et al. 1996). Given the dearth of data, further genetic information on the Anatolian populations is needed, both for the validation of the stated hypothesis and for an improved understanding of the relationships between the present-day Turks and the populations of the areas surrounding Anatolia, the Mediterranean basin, and Europe. We report the analysis of a sample of 93 Turkish subjects for the following 15 protein polymorphisms: B subunit of coagulation factor XIII (FJ3B), alpha-l-acid glycoprotein or orosomucoid 1 (ORMI), alpha-2HSglycoprotein (AHSG), properdin factor B (BF), the apolipoproteins E (APOE) and C-II (APOC2), the fourth (C4A, C4B), sixth (C6), and seventh (C7) components of the human complement, haptoglobin (HP), group-specific component (GC), glyoxalase 1 (GLOI), esterase D (ESD), and phosphoglucomutase 1 (PGMI). Most of these polymorphisms (ESD, GC, PGM], F13B, ORMI, AHSG, Cd, C7, APOC2, BF, C4A, C4B) have not yet been studied in the population of Turkey.

Materials and Methods

Sample. Blood specimens were collected in tubes containing EDTA at Bogazici University, Istanbul, Turkey, from unrelated consenting individuals of both sexes. The birthplaces of the parents of each subject were ascertained by interview and are indicated in Figure 1. Six of the 93 sampled individuals declared parental birthplaces in European Turkey, and 2 were in Cyprus (Turkish area); for the remaining 85 individuals, parental birthplaces were uniformly distributed in the various regions of Anatolia. After venipuncture, serum, plasma, and red blood cells were separated, immediately frozen at - 80oC, and maintained at this temperature until analysis.