Avon Longitudinal Study of Parents and Children (ALSPAC)
Cohort description: ALSPAC is a population based longitudinal pregnancy-ascertained birth-cohort in the Bristol area of the UK. Specifically, recruitment sought to enrol all pregnant women with an estimated delivery date between 1st April 1991 and 31st December 1992
1, who where residents within three Health Districts of the former administrative county of Avon
2. The initial cohort included 14,541 pregnancies and additional children eligible using the original enrolment definition were recruited up to the age of 18 years, increasing the total number of pregnancies to 15,247 (4.1% Non-White mothers). Information on the children from these pregnancies is available from questionnaires, clinical assessments, linkage to health and administrative records as well as biological samples including genetic and epigenetic information. Ethical approval was obtained from the ALSPAC Law and Ethics Committee (IRB00003312) and the Local Research Ethics Committees, and written informed consent was provided by all parents.
Intelligence measure: Intelligence in ALSPAC children at the age of 8 years was measured with the Wechsler Intelligence Scale for Children (WISC-III). A short version of the test consisting of alternate items only (except the Coding task) was applied by trained psychologists. Verbal (information, similarities, arithmetic, vocabulary, comprehension) and performance (picture completion, coding, picture arrangement, block design, object assembly) subscales were administered, each subtest was age-scaled according to population norms and a summary score for total IQ derived. Pertinent to this analysis, we generated sex and principal component (i.e. the two most significant principal components from Eigenstrat analysis, see below) adjusted Z-standardised intelligence quotient (IQ) scores for independent ALSPAC children with information on total IQ and genome-wide data. For this, IQ scores within a range of ±4SD relative to the total ALSPAC sample were regressed on sex (coded as 1 = male and 2 = female) and the principal components. The residuals were Z-transformed and subjected to genome-wide analysis.