Child psychopathology and lower cognitive ability: a general population twin study of the causes of association

Abstract

Previous work has demonstrated associations between lower cognitive ability and childhood and adult non-psychotic psychopathology. As both cognitive ability (CA) and child psychopathology (CP) are influenced by genetic factors, one explanation for the association is that they are the pleiotropic manifestations of the same underlying genetic factors.

Genetics, genes, genomics and g

“…38,39 An association with g has also been reported for a gene involved in controlling homocystein/folate metabolism. 40 Because research on dementia will be the immediate source of more molecular genetic research on g as in the CTSD study in this issue, 4 it is worth noting that the apolipoprotein gene, which shows a strong association with dementia, shows no association with g in childhood 41,42 or in adults. 43 Despite the power of the two studies in this issue to detect QTL associations, replication will be crucial because the track record for replicating candidate gene associations is not good.…”

“…35 Two papers on molecular genetics in this issue are distinctive in that they focus on normal variation in g using large unselected samples. 1,4 They report positive associations between normal variation in g and two candidate genes: Cathepsin D (CTSD; 4) and cholinergic muscarinic 2 receptor (CHRM2; 1). The effect sizes are small (heritabilities of 3 and 1%, respectively) as expected for QTLs, but are easily detected as significant with the large sample sizes of these studies (767 and 828, respectively).…”

“…One such issue is the use of functional polymorphisms. In the CTSD study, 4 the candidate gene polymorphism is functional (C4T, Ala4Val); in the CHRM2 study, 1 the single nucleotide polymorphism (SNP) is in the 3 0 untranslated region of the gene. The use of functional polymorphisms involves direct association that greatly increases power because it tests the hypothesis that the polymorphism is the QTL rather than relying on the marker being in linkage disequilibrium with the QTL associated with the trait (indirect association).…”

“…There was also a related article in a previous issue of Molecular Psychiatry. 4 These four papers represent the range of research on genetics (quantitative genetic twin studies), genes (molecular genetic attempts to identify genes) and genomics (understanding the function of genes). The goal of this editorial is to put these papers in perspective.…”

Heritability of Intelligence

“…Moreover, at least 200 single-gene disorders include mental retardation among their symptoms (Inlow & Restifo, 2004 (Goodman, 1995). In a study (Jacobs et al, 2002) conducted in a sample of 376 twin pairs aged 8 to 14 from the EFPTS, it was found that genetic factors accounted for 84% of this modest but significant phenotypic correlation (r = -.19; see Figure 1). It was concluded that in children three different genetic factors may exist: one that solely affects the liability to child psychopathology, one that had only an effect on 'g' and one that influences both phenotypes.…”