Inbreeding in Southeastern Spain : The Impact of Geography and Demography on Marital Mobility and Marital Distance Patterns (1900-1969)

Genetic variation patterns of β-thalassemia in Western Andalusia (Spain) reveal a structure of specific mutations within the Iberian Peninsula

BACKGROUND

Analyses of the genomic variation in the western Mediterranean population are being used to reveal its evolutionary history and to understand the molecular basis of particular diseases.

AIM

To observe the β-thalassemia mutational spectrum in western Andalusia, Spain, in the context of the Mediterranean. In addition, associations between disease and neutral gene variants within the β-globin gene (HBB) were also evaluated.

SUBJECTS AND METHODS

This study included 63 unrelated individuals diagnosed with β-thalassemia. In addition, 97 unrelated, healthy subjects of the same territory were also analysed as proxies of the normal genetic background. Allele associations and population genetic structure analyses were performed using different methodologies.

RESULTS

Data have revealed a rather restricted spectrum of β-thalassemia mutations in the analysed sample. Although the detected variants fit well with the Mediterranean pattern, certain singularities support a structure of some specific β-thalassemia alleles. The IVSI-1 (G > A) shows a strong regionalisation. The spatial correlogram revealed a typically narrow wave structure, presumably linked to genetic isolation and genetic drift.

CONCLUSIONS

The long history of endemic malaria in the study territory, the rather high consanguinity rates among its autochthonous population, and other demographic features have been used here to understand the western Andalusian β-thalassemia molecular portrait.

Fine-scale population structure in five rural populations from the Spanish Eastern Pyrenees using high-coverage whole-genome sequence data

The area of the Spanish Pyrenees is particularly interesting for studying the demographic dynamics of European rural areas given its orography, the main traditional rural condition of its population and the reported higher patterns of consanguinity of the region. Previous genetic studies suggest a gradient of genetic continuity of the area in the West to East axis. However, it has been shown that micro-population substructure can be detected when considering high-quality NGS data and using spatial explicit methods. In this work, we have analyzed the genome of 30 individuals sequenced at 40× from five different valleys in the Spanish Eastern Pyrenees (SEP) separated by less than 140 km along a west to east axis. Using haplotype-based methods and spatial analyses, we have been able to detect micro-population substructure within SEP not seen in previous studies. Linkage disequilibrium and autozygosity analyses suggest that the SEP populations show diverse demographic histories. In agreement with these results, demographic modeling by means of ABC-DL identify heterogeneity in their effective population sizes despite of their close geographic proximity, and suggests that the population substructure within SEP could have appeared around 2500 years ago. Overall, these results suggest that each rural population of the Pyrenees could represent a unique entity.

Consanguineous marriages among Andalusian Gitanos/Calé: a genealogical analysis (1925-2006)

Using data from the family and genealogical reconstitutions of the Gitano population of 22 contiguous localities in eastern Andalusia, Spain, this study analysed the intensity, structure and historical evolution of consanguinity in 3056 couples formed from 1925 to 2006. Of these unions, 54.8% were consanguineous, and 28.7% involved relatives up to and including second cousins, resulting in a mean coefficient of inbreeding up to the third degree α3 = 12.4 × 10-3. The rest of the consanguineous unions (26.1% of all) involved more-distant relatives, such as third cousins, fourth cousins and so forth. When all consanguinity degrees found in the genealogical reconstitution were considered, the total mean coefficient of inbreeding was αt = 14.8 × 10-3. The merging of families and pedigrees generated a complex genealogical network with many inbreeding loops and important founder effects. This network revealed a high rate (62%) of Multiple Consanguineous Marriages (MCMs) in which second and subsequent consanguineous ties increased inbreeding levels by a fifth (20.5%). The accumulation of multiple degrees of distant relatedness, many of which had little social or biological importance, has contributed to a significant increase in inbreeding rates. Among Gitano people, intra-family marriages have remained common in the last decades, in sharp contrast to other Spanish populations. Hence the highest rates of close consanguinity (34%) and inbreeding (α3 = 14.6 × 10-3) were found in the 1960s, the decade that saw the onset of Spain's socioeconomic modernization, internationalization and massive migration. These are among the highest rates of inbreeding found in any European population, including the most endogamous Spanish isolates. They reveal marriage strategies not constrained primarily by geographical barriers, but by ethnocultural separation. Interestingly, in recent decades mixed marriages have been increasing rapidly in this minority, although they are compatible with high rates of consanguinity. Gitano secular endogamy is breaking up, but not uniformly.