Consanguinity in the Bishopric of Ourense (Galicia, Spain) from 1900 to 1979.

BACKGROUND: Knowledge of the levels of inbreeding in the human population is interesting because it is one of the characteristics that conditions its genetic structure and has important genetic-medical repercussions in the descendants of marriages between close relatives. Galicia (north-west Spain) is a region with very special geographic, historic and social characteristics that makes it particularly interesting for consanguinity studies. PRIMARY OBJECTIVE: The object of this investigation is the study of the levels of inbreeding and the structure of consanguinity in rural area of the Dioceses of Ourense (Galicia) during the period 1900-1979. SUBJECTS AND METHODS: In the study, data corresponding to 437 parishes, integrated in 80 municipalities of the rural area of the Dioceses of Ourense were analysed. In the period studied, of a total of 110 128 marriages, 9010 took place between biologically related individuals up to the level of second cousins. The rate of consanguinity and the average coefficient of inbreeding of the population, as well as the percentage of the different types of consanguineous marriages, were calculated. MAIN OUTCOMES AND RESULTS: The rate of consanguinity for the period 1900-1979 is 8.18% and the average coefficient of inbreeding is 3.0662 x 10(-3). The most frequent type of consanguineous marriage is between second cousins (4.00% of all marriages). There is a notably high frequency of marriages of multiple relationships (0.52%) and the frequency of uncle-niece or aunt-nephew marriages is 0.16%. The average value of the M22/M33 ratio is 0.66 and during the 80 years studied, with regard to the temporal variation of the average coefficient of inbreeding, the annual values followed a polynomial curve with an inflection point in 1921. CONCLUSIONS: The highest values of consanguinity detected in Galicia, for the same period, were registered in the Dioceses of Ourense and the high rate of uncle-niece or aunt-nephew marriages habitual in this region was confirmed. The latter is explained by the important incidence in the Galician population of the migration to America at the end of the 19th and beginning of the 20th century. However, when the relative frequency of this type of marriage with respect to the total number of consanguineous marriages is calculated, it has relatively low values due to the high proportion of marriages between second cousins and marriages of multiple relationships, the highest in Galicia for an equal period of time. The rate of marriages between first cousins is also the highest in Galicia, confirming a phenomenon that appears to be common in the rural areas of the northern area of the Iberian Peninsula.

Evolution of consanguinity in the Bishopric of Lugo (Spain) from 1900 to 1979.

BACKGROUND: The levels of consanguinity in human populations are known to be influenced by demographic and geographical factors, and by socio-cultural customs that govern spouse choice. Within the general model applicable to the populations of Western Europe, Galicia (north-west Spain) is a region that is especially interesting, due to its geographical and historical peculiarities that could have conditioned its behaviour pattern with respect to consanguinity. PRIMARY OBJECTIVE: The object of this paper is to analyse the evolution of the consanguinity structure levels in the rural population of the Bishopric of Lugo (Galicia) during the period 1900-1979. SUBJECTS AND METHODS: The study covers a total of 752 parishes included in 52 municipalities of the rural area of the Bishopric of Lugo. Of a total of 117,583 marriages in the period studied, 6701 were between biologically related individuals up to the level of second cousins. The percentage of the different types of consanguineous marriages, the consanguinity rates, and the average coefficient of inbreeding of the population was calculated. Also, for the analysis of the temporal variation of consanguinity, version 3.01 of Jandel Scientific's Table Curve program was used. MAIN OUTCOMES AND RESULTS: The consanguinity rate for the whole of the period is 5.70% and the average coefficient of inbreeding is 2.2477 x 10(-3), values which fall within the observed range for Spanish populations. As for the consanguinity structure, the most frequent types of consanguineous marriages are between second cousins (2.65% of all marriages), but the high proportion of marriages between uncles/nieces or aunts/nephews (0.16%) and first cousins (2.12%) with regard to the total number of marriages should be emphasized. The average value of the M22/M33 ratio is 0.80, and throughout the study period it was above the 0.25 expected in conditions of panmixia. Regarding the evolution of the average coefficient of inbreeding, its annual values fit a polynomial regression curve with one ascending and one descending branch and an inflection point in the year 1919. CONCLUSIONS: As in other rural areas of Galicia, the structure of consanguinity in the Bishopric of Lugo is characterized by the high proportion of marriages between uncles/nieces or aunts/nephews and first cousins, a phenomenon which appears to be generalized in the rural populations of northern Spain. It is suggested that the high proportion of uncle/niece marriages that have been found in the population studied are very probably due to the important migratory phenomenon which took place in this region at the end of the 19th century and in the first third of the 20th century.

Local differences in the Archbishopric of Santiago de Compostela (Galicia, Spain) in relation to the consanguinity structure, 1900-1979.

The microgeographic variability of consanguinity in the Archbishopric of Santiago de Compostela (Galicia) between 1900 and 1979 was studied. This Archbishopric covers 106 local councils integrated by 964 parishes, of which 677 (70.23%) were analyzed. Of the 307,094 marriages counted within this period, 15,739 corresponded to weddings between biologically related couples. Within the Archbishopric, eight geographical regions were considered: six coastal regions (Golfo Artabro, Bergantiños, Fisterra, Xallas, Santiago Oeste, and Rías Baixas) and two inland regions (Santiago Este and Terra de Montes). In order to evaluate the differences and similarities among them, the frequencies of all types of marriages (consanguineous and nonconsanguineous) were considered. First, a hierarchical grouping of the regions based on their chi-squared distances was performed. Then, in order to analyze relationships that are exclusively due to the structure of consanguinity, a correspondence analysis was performed and only the frequency of the different types of consanguineous marriages was taken into account. The results from both statistical analyses indicate special features of the Xallas region, both in the level of inbreeding (8.75%, the highest in the Archbishopric) and in the structure of consanguinity, for which a high proportion of uncle-niece marriages was found (6.22% of all consanguineous marriages). In all cases the structure of consanguinity provides informative nuances on the differences and similarities among population groups.

Evolution of consanguinity in the Archbishopric of Santiago de Compostela (Spain) during 1900-1979.

We present a study of the frequencies of the different types of consanguineous marriages, up to the level of second cousins, using as a source the ecclesiastical dispensations given from 1900 to 1979 in the Archbishopric of Santiago de Compostela (Galicia, Spain). We also report the rate of consanguinity, the average coefficient of inbreeding, and its evolution. From 1900 to 1979, 15,739 consanguineous marriages were registered, corresponding to 25 different categories of relationship. The rate of consanguinity of the total number of consanguineous marriages is 5.13% and the average coefficient of inbreeding is 1.94 x 10(-3), values that are within the wide range of variability found in other Spanish populations. Spain is characterized, with regard to the rest of Western Europe, by a high level of inbreeding with a late and rapid decrease in this factor. The most relevant aspect of the structure of consanguinity lies in the high frequency of marriages between close relatives: 0.16% uncle-niece or aunt-nephew marriages and 1.62% marriages between first cousins, both values with respect to the total number of marriages. This phenomenon appears to be generalized throughout northern Spain. The evolution of the total consanguinity lends itself to a polynomial curve model. The fitted curve of the evolution of the average coefficient of inbreeding has an ascending branch and a descending branch, with the inflection point situated in the year 1918; the regression lines, for both the ascending and the descending branches, have regression coefficients significantly different from 0 (p < 0.001).

Additional data on PGP genetic transmission in family groups.

PGP (phosphoglycolate phosphatase, EC 3.1.3.18.) gentic studies were performed in 188 families including a total of 415 offspring in the Galician population. The results are in agreement with the formal hypothesis of three codominant alleles at an autosomal locus. No silent alleles have been observed.