A study of contemporary levels and temporal trends in inbreeding in the Tangier Island, Virginia, population using pedigree data and isonymy

Abstract

In this study we describe inbreeding in a large pedigree from Tangier Island, Virginia, in which we compare two commonly used methods to estimate inbreeding in humans: pedigree and isonymy (identical surnames of spouses). Genealogical data on 3,512 individuals dating back to 1722 were used. Using the pedigree method, we determined an average inbreeding coefficient (F) of 0.00873 for the community as a whole, and 0.018 for inbred individuals. Analysis of temporal trends showed that inbreeding began around 1800 and peaked at 0.0109 in 1824-1849 and 1875-1899. Thereafter, inbreeding steadily declined to 0.00565 in 1975-1997. Analysis of pedigree structure complexity over time showed that close consanguinity contributes to inbreeding in the earlier cohorts, and remote consanguinity accounts for much of the inbreeding in the later cohorts. The number of common ancestors increases over time, as does the number of paths connecting inbred individuals to these common ancestors. Inbreeding estimates based on the isonymy approach yielded a 2.2-fold higher value of F (0.01945) compared to the pedigree method. Total isonymy estimates over 25-year cohorts overestimated inbreeding values from pedigree data between 1. 5-8-fold. We speculate that the overestimation is probably due to the inability of our data to satisfy the method's assumption of monophyletic origin of each surname. In conclusion, inbreeding in the Tangier Island population is consistent with the isolated nature of its population, and temporal trends reflect patterns in emigration and a breakdown in isolation over time.

FADS genetic variants and ω-6 polyunsaturated fatty acid metabolism in a homogeneous island population

“…This has been demonstrated in other isolated populations, such as the Hutterites, Finish, and Amish, for multiple complex disorders like bipolar disease, allergic asthma, and familial combined hyperlipidemia, among others ( 39 ). Although the Tangier Island population is isolated and inbred, our previous work has demonstrated that inbreeding levels are refl ective of an avoidance of close consanguinity ( 26 ), rendering Tangier Island generalizable to other European-ancestry populations as refl ected in similar LD patterns and allele frequencies to publicly available databases ( Fig. 2 ; R. A. Mathias, unpublished observations).…”

“…At the time of subject recruitment (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001), the population was composed of approximately 650 individuals, and the isolated nature of the island has led to sustained low levels of inbreeding ( 26 ). Briefl y, the average inbreeding coeffi cient (F) for the entire Tangier Island population (dating back to 1722) is 0.009 (range, 0.000-0.156; n = 3,512).…”

“…All participants are connected in a single, 13-generational pedigree with an average inbreeding coeffi cient refl ective of an avoidance of close consanguinity (average F = 0.003 per mating summed over an average number of paths connecting each pair = 300) ( 26,27 ). All subjects gave written, informed consent as approved by The Johns Hopkins University Institutional Review Board.…”

Analysis of the French National Registry of unrelated bone marrow donors, using surnames as a tool for improving geographical localisation of HLA haplotypes

“…Surnames have proved to be useful for describing the population structure, and isonymy makes it possible to evaluate isolation and consanguinity (see the recent bibliography in Barrai et al, 13 Mathias et al, 14 RodriguezLarralde, 15 Lasker et al, 16 Sykes et al, 17 Manni et al, 18 Barrai et al, 19,20 Caravello et al, 21 Gagnon et al, 22 ). They are also frequently used as a tool to identify individuals' geographical origin (see the recent bibliography in Chan, 23 GarzaChapa et al, 24 De Silvesti and Guglielmino, 25 Pollock et al, 26 Jacobs and Landerdale, 27 Rudan, 28 Carta et al, 29 Brancatelli et al 30 ).…”

Pedigree Structure and Kinship Measurements of a Mid-Michigan Community: A New North American Population Isolate Identified

“…While such isolates exist, including the Hutterite communities (Steinberg AG 1967), Old Order Amish communities (Agarwala et al 2003), and residents of Tangier Island (Mathias et al 2000), the relatively short time since initial immigration, the high mobility of citizens, and the paucity of distant historical and genealogical records make the identification of new population isolates difficult.…”