Inbreeding coefficients and degree of consanguineous marriages in Spain: a review

The landscape of autosomal-recessive pathogenic variants in European populations reveals phenotype-specific effects

The number and distribution of recessive alleles in the population for various diseases are not known at genome-wide-scale. Based on 6,447 exome sequences of healthy, genetically unrelated Europeans of two distinct ancestries, we estimate that every individual is a carrier of at least 2 pathogenic variants in currently known autosomal-recessive (AR) genes and that 0.8%-1% of European couples are at risk of having a child affected with a severe AR genetic disorder. This risk is 16.5-fold higher for first cousins but is significantly more increased for skeletal disorders and intellectual disabilities due to their distinct genetic architecture.

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.

Frequency and characteristics of familial melanoma in Spain: the FAM-GEM-1 Study

INTRODUCTION

Familial history of melanoma is a well-known risk factor for the disease, and 7% melanoma patients were reported to have a family history of melanoma. Data relating to the frequency and clinical and pathological characteristics of both familial and non-familial melanoma in Spain have been published, but these only include patients from specific areas of Spain and do not represent the data for the whole of Spain.

PATIENTS AND METHODS

An observational study conducted by the Spanish Group of Melanoma (GEM) analyzed the family history of patients diagnosed with melanoma between 2011 and 2013 in the dermatology and oncology departments.

RESULTS

In all, 1047 patients were analyzed, and 69 (6.6%) fulfilled criteria for classical familial melanoma (two or more first-degree relatives diagnosed with melanoma). Taking into account other risk factors for familial melanoma, such as multiple melanoma, pancreatic cancer in the family or second-degree relatives with melanoma, the number of patients fulfilling the criteria increased to 165 (15.8%). Using a univariate analysis, we determined that a Breslow index of less than 1 mm, negative mitosis, multiple melanoma, and a history of sunburns in childhood were more frequent in familial melanoma patients, but a multivariate analysis revealed no differences in any pathological or clinical factor between the two groups.

CONCLUSIONS

Similar to that observed in other countries, familial melanoma accounts for 6.6% of melanoma diagnoses in Spain. Although no differences in the multivariate analysis were found, some better prognosis factors, such as Breslow index, seem more frequent in familial melanoma, which reflect a better early detection marker and/or a different biological behavior.

Reproductive pattern in consanguineous and non-consanguineous marriages in La Cabrera, Spain

BACKGROUND

Among determinants of the structure of human populations, consanguineous marriages can be useful in determining to what extent they influence the genetic structure of the population. This knowledge may be gained by comparing the reproductive performance of related and non-related couples. The population studied, La Cabrera, is a mountainous region in the Leon province (north-western Spain). It includes four neighbouring municipalities with similar geographic, climatic and ecological features with 37 parishes occupying an area of 784.2 km(2), of which only 1.5% is arable. The number of inhabitants remained stable from 1887 (9526 inhabitants) to 1960 (8984), when due to emigration it began to decrease. The average inbreeding coefficient (alpha) for the period 1880-1989 (up to third degree) was 4.82 x 10(-3).

AIM

The objective of this analysis was to evaluate the possible factors determining the differences between consanguineous and non-consanguineous families residing in La Cabrera during the period 1880-1959.

SUBJECTS AND METHODS

To study the structure and dynamics of each couple, families were reconstituted for the period 1880-1959 using demographic data corresponding to births, deaths and marriages obtained from parish registers. This procedure provided information on each couple's reproductive history through information concerning the mates' deaths as well as their offspring's births and deaths. Principal component analysis revealed the existence of three factors that together explained 57% of the reproductive pattern variability of La Cabrera.

RESULTS

The first component (eigenvalue: 3.56) correlated positively with the number of live births and with the duration of the reproductive period. Component II (eigenvalue: 1.54) had a positive correlation with variables describing the beginning of the marital union, and with those indicating its ending. Finally, component III (eigenvalue: 1.13) reflected a negative association with the two variables that described neonatal and post-neonatal mortality. The above demographic variables represented the reproductive process in La Cabrera adequately. Fertility was the variable that offered the best explanation of the reproductive pattern (32%), followed by the marital structure (13%) and the infant mortality (12%).

CONCLUSION

In the La Cabrera population, consanguinity appears as a socio-cultural process that affects the reproductive dynamic. Consanguinity modifies the marital structure and alters the reproductive pattern, prolonging the reproductive period, which results in a greater number of offspring. Lower infertility rates and the possible compensatory effect for infant mortality may reflect biological factors making the wife's reproductive period more efficient.