Eaves Lindon J, Silberg Judy L
Virginia Institute for Psychiatric and Behavioral Genetics, Department of Human and Molecular Genetics, Virginia Commonwealth University, Richmond, VA 23298-0003, USA.
J Child Psychol Psychiatry. 2008 Nov;49(11):1201-10. doi: 10.1111/j.1469-7610.2008.01956.x.
If the adaptive significance of specific fears changes with age, the genetic contribution to individual differences may be lowest at the age of greatest salience. The roles of genes and environment in the developmental-genetic trajectory of five common childhood fears are explored in 1094 like-sex pairs of male and female monozygotic and dizygotic twins assessed on up to three occasions during adolescence (ages 8-18 years).
Dichotomous self-ratings of a cluster of five correlated fears from Ollendick's schedule of fears (FSSC-R) were extracted for subjects at each occasion of assessment. The effects of genes and environment on overall level of fears and rates of adolescent decline were explored by fitting an item-response theory ('IRT') model that allowed for individual genetic and environmental differences in initial fear level ('intercept') and rates of adolescent change ('slope') across the repeated waves of measurement. Different forms of the model were explored using Markov Chain Monte Carlo (MCMC) methods to derive the posterior distribution of subject and item parameters from the raw responses.
Additive genetic differences affect the common factor underlying the five fear-items. The same genes also affect rates of change with age, especially in boys. Male adolescents with higher overall genetic predisposition to childhood fears tended to show slower recovery with age than subjects with relatively low initial values. Thus, the genetic variance apparently increases with age.
This finding is consistent with a prediction that the regulation of genetic differences will be strongest, and thus the additive genetic variance will be smallest, at the age when the particular stimulus is most salient. Items differed in the extent to which they were sensitive to underlying random differences in the rate of developmental change. Individual differences in rates of change with age were more marked in boys than girls.
如果特定恐惧的适应性意义随年龄变化，那么在最显著的年龄，基因对个体差异的贡献可能最低。在1094对同性别的男性和女性同卵双胞胎及异卵双胞胎中，研究了基因和环境在五种常见儿童期恐惧的发育遗传轨迹中的作用，这些双胞胎在青春期（8至18岁）接受了多达三次评估。
在每次评估时，从奥伦迪克恐惧量表（FSSC-R）中提取对一组五个相关恐惧的二分法自评数据。通过拟合一个项目反应理论（IRT）模型，探讨基因和环境对恐惧总体水平和青少年恐惧下降率的影响，该模型允许在重复测量的各个阶段，个体在初始恐惧水平（“截距”）和青少年变化率（“斜率”）上存在遗传和环境差异。使用马尔可夫链蒙特卡罗（MCMC）方法探索模型的不同形式，以便从原始反应中推导出受试者和项目参数的后验分布。
加性遗传差异影响五个恐惧项目背后的共同因素。相同的基因也影响随年龄的变化率，尤其是在男孩中。总体上对儿童期恐惧具有较高遗传易感性的男性青少年，与初始值相对较低的受试者相比，随着年龄增长往往恢复较慢。因此，遗传方差显然随年龄增加。
这一发现与一项预测一致，即在特定刺激最显著的年龄，遗传差异的调控最强，因此加性遗传方差最小。不同项目对发育变化率潜在随机差异的敏感程度不同。男孩随年龄变化率的个体差异比女孩更明显。
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