Roberts D F, Roberts M J, Johnston A W
Department of Human Genetics, University of Newcastle upon Tyne, UK.
Hum Genet. 1991 May;87(1):57-60. doi: 10.1007/BF01213093.
Pedigrees of all known cases, on Shetland, of Down's syndrome, cytogenetically confirmed as trisomy 21, and of a control for each patient matched by birth date, sex and birth place, were traced over a minimum of eight generations. Mean kinship coefficients in all pairs of Down's syndrome patients and in all pairs of controls were similar. The kinship between the father and mother of each case shows that the parents are more closely related than the general level of relationship in the population, suggesting some recessive element in the etiology. It is argued that the effect of the resulting increased homozygosity would be to prevent the loss of the conceptus that occurs in the majority of trisomy 21 conceptions.
对设得兰群岛上所有已知的唐氏综合征病例（经细胞遗传学确认是21三体）以及为每位患者按出生日期、性别和出生地匹配的对照者的谱系进行了至少八代的追溯。所有唐氏综合征患者对以及所有对照者对的平均亲缘系数相似。每个病例的父母之间的亲缘关系表明，父母之间的亲缘关系比人群中的一般关系更为密切，这表明病因中存在一些隐性因素。有人认为，由此导致的纯合性增加的影响将是防止大多数21三体妊娠中发生的胚胎丢失。
