Sex linked versus autosomal inbreeding coefficient in close consanguineous marriages in the Basque country and Castile (Spain): genetic implications

Abstract

SummaryPedigree structures of 161 uncle/niece-aunt/nephew and 4420 first cousin consanguineous marriages registered during the 19th and 20th centuries in two large and very different Spanish regions have been analysed and their genetic consequences evaluated. The frequencies of the different pedigree subtypes within each degree of relationship were quite similar in both populations despite significant heterogeneity in inbreeding patterns. The mean X-linked inbreeding coefficient (Fx) for each type of cousin mating was calculated and compared to that expected for autosomal genes (F). The effect of genealogical structure on theFx/Fradio was compared to different cultural populations worldwide. Preferentiality and avoidance of close consanguinity along with specific types of pedigrees are discussed on the basis of premarital migration and sociocultural rules still deeply rooted in certain human groups. By admitting that the observedFxcoefficient is usually higher thanFin most human populations some remarks have been made in terms of population genetic risk.

Inbreeding Coefficients for X‐linked and Autosomal Genes in Consanguineous Marriages in Spanish Populations: The Case of Guipúzcoa (Basque Country)

“…Maternal first cousin pedigree subtypes ( f x > 0) are slightly more common in Spain than paternal subtypes (Calderón et al 1995; present study) but this difference varies considerably from region to region (χ 2 = 25.028, df = 9, p = 0.003). The distortion seems to be caused by Guipúzcoa, which has a rather high rate of maternal parallel first cousin subtypes (M22–0: f x = 3/16); the χ 2 test yielded a high adjusted residual value.…”

“…As can be seen in Table 3, the F x / F ratios for first cousins are higher in all cases than 1.25. A review of variations in F x / F values among a number of worldwide human populations can be found elsewhere (Calderón et al 1995).…”

“…The frequency of X‐linked disease is obtained using a similar formula: K x = c ( q 2 + (1 − q ) q f 22 X )/( q 2 + (1 − q ) q F X ) where f 22X is the pedigree inbreeding coefficient for first cousin subtypes and F X is the mean population inbreeding coefficient for X‐linked genes. For empirical values of c and q , K x ≈ c ( q + F x ) (see Calderón et al 1995). Interestingly, recent consanguinity studies have suggested that population substructures need to be taken into account to accurately estimate disease incidence (Overall et al 2003).…”

“…To date, little is known about the mean inbreeding coefficient for X‐linked genes ( F x ) in Spanish or other European populations, or about how it compares to the mean inbreeding coefficient for autosomal genes ( F ). Research in this field would be of particular interest for furthering knowledge of human population genetics, the relationship between biology and culture, and genetic risk (Barrai et al 1962; Hajnal, 1963; Hedrick & Parker 1997; Calderón et al 1995).…”

Consanguinity in two Uruguayan cities: historical evolution and characteristics (1800-1994)

“…More recently, Orioli et al (1982) analysed 70 first cousin marriages and determined that A unions are the most frequent, followed by D unions (both parallel marriages), in agreement with our study. For Spain, a comprehensive analysis of marriages from the Basque Country and Castile (Spain) showed a preference for subtypes A and B in the Basque Country and a preference for subtypes B and A in Central Spain (Caldero´n et al 1995).…”