Abstract
How genes contribute to cognition is a perennial question for psychologists and geneticists. In the early 21st century, familial studies, including twin studies, supported the theory that genetic variations contribute to differences in cognition, but have been of little practical use to clinical and educational practitioners as no individual predictions can be made using such data; heritability cannot predict the impact of environmental factors or intervention programs. With the sequencing of animal genomes and the development of molecular genetics, new methodologies have been developed: gene targeting (replacing a functional gene with a neutral gene by homologous recombination), transgenesis (overexpressing one gene or a set of genes from one species in another species), and genome-wide scans and quantitative trait loci mapping (a strategy for identifying chromosomal regions involved in complex traits). Association studies can be performed to find associations between allelic forms and variations in IQ. Genes linked to “normal” variations in cognition have been detected but for the moment such discoveries have had no direct applications in a clinical setting; the number of genes identified as being linked to intellectual impairment has increased rapidly. Links have been reported between chromosomal deletions and triplications and behavioral phenotypes. The identification of mechanisms involved in genetic diseases should have long-term consequences on educational and/or psychological support programs as well as on health care. Psychologists need to keep up to date on advances in research establishing relationships between genetics and intellectual disability and will thus be able to refer children with cognitive impairments to specialized care services.
References
2002). Classical twin studies and beyond. Nature Reviews Genetics, 3, 872–882.
(1981). Familial studies of intelligence: A review. Science, 212, 1055–1059.
(2003). Spatial learning in the 5-HT1B receptor knockout mouse: Selective facilitation/impairment depending on cognitive demand. Learning & Memory, 10, 466–477.
(2005). SNPs, microarrays and pooled DNA: Identification of four loci associated with mild mental impairment in a sample of 6000 children. Human Molecular Genetics, 14, 1315–1325.
(2007). Déficiences intellectuelles et intégration sociale. Wavre, Belgique: Mardaga.
(1992). The separation of genetic from maternal effects. In , Techniques for the genetic analysis of brain and behavior: Focus on the mouse (pp. 111–126). Amsterdam: Elsevier.
(1991). The Y chromosome effect on intermale aggression in mice depends on the maternal environment. Genetics, 129, 231–236.
(1999). Maternal effects in behavior genetic analysis. In , Neurobehavioral genetics: Methods and applications (pp. 187–197). Boca Raton: CRC Press.
(2004). Failure to obtain reliable determination of chorion type using parent information: Confirmation with French data. Twin Research, 7, 13–15.
(2007). Moderation of breastfeeding effects on the IQ by genetic variation in fatty acid metabolism. Proceedings of the National Academy of Science USA. 18860–18865.
(2005). Delineation of the clinical phenotype associated with OPHN-1 mutations based on the clinical and neuropsychological evaluation of three families. American Journal of Medical Genetics, A. 138, 314–317.
(2002). Effects of pre- and postnatal stimulation on developmental, emotional, and cognitive aspects in rodents: A review. Developmental Psychobiology, 41, 373–387.
(1979). Effect of type of placentation on birthweight and its variability in monozygotic and dizygotic twins. Acta Geneticae Medicae et Gemellologiae, 28, 41–50.
(2006). Academic impairment is the most frequent complication of neurofibromatosis type-1 (NF1) in children. Behavior Genetics, 36, 604–660.
(2004). COMT gene polymorphism is associated with declarative memory in adulthood ans old age. Behavior Genetics, 34, 533–539.
(2001). A genetic neuroscience approach to human cognition. European Psychologist, 6, 241–253.
(1998). The uterine environment enhances cognitive competence. Neuro-Report, 9, 619–623.
(1997). The heritability of IQ. Nature, 388, 468–470.
(1976). The Genetics of Behaviour. Sunderland, Mass: Sinauer Associated Inc.
(1963). Genetics and intelligence: A review. Science, 142, 1477–1479.
(2008). Individual differences in executive function are almost entirely genetic in origin. Journal of Experimental Psychology: General, 137, 201–225.
(1960). Behavior genetics. New York, NY: Wiley.
(1981). Mismeasure of Man. New York, NY: Norton & Co. (Revised 1996). Traduit en Français sous le titre La Mal-Mesure de l’Homme (1997). Paris: Odile Jacob.
(1999). Long term effect of placental type on anthropometrical and psychological traits among monozygotic twins: A follow up study. Twin Research, 2, 212–217.
(2009). The heritability of general cognitive ability increases linearly from childhood to young adulthood. Molecular Psychiatry. Advance Online Publication. doi:10.1038/mp.2009.55.
(1967a). Behavior-genetic analysis. New York, NY: McGraw-Hill Book Company.
(1967b). Behavior-genetic, or “experimental”, analysis: The challenge of science versus the lure of technology. American Psychologist, 22, 118–130.
(1975). Jensenism: The bankruptcy of “Science” without scholarship. Educational Theory, 25, 3–27.
(1929). The relative effect of nature and nurture influences on twins differences. Journal of Educational Psychology, 29, 345–348.
(2001). Heritability estimates of intelligence in twins: Effect on chorion type. Behavior Genetics, 31, 209–217.
(2005). The first ‘classical’ twin sutdy? Analysis of refractive error using monozygotic and dygotic twins published in 1922. Twin Research and Human Genetics, 8, 198–200.
(2001). The influence of zygosity and chorion type on fat distribution in young adult twins consequences for twin studies. Twin Research, 4, 356–364.
(2002). A functional polymorphism in the COMT gene and performance on a test of prefrontal cognition. American Journal of Psychiatry, 159, 652–654.
(1997). A twin-pronged attack on complex traits. Nature Genetics, 17, 387–392.
(2002). Genetic approaches to molecular and cellular cognition: A focus on LTP and learning and memory. Annual Review of Genetics, 36, 687–720.
(2001). The genetics of cognitive processes: Candidate genes in humans and animals. Behavior Genetics, 31, 511–531.
(1992). Methodology for genetic studies of twins and families. Kluwer Academic Publishers: Dordrecht.
(2006). Enriched environments, experience-dependent plasticity and disorders of the nervous system. Nature Review Neuroscience, 7, 697–709.
(2006). The quest for quantitative trait loci associated with intelligence. Intelligence, 34, 513–526.
(2001). Genetics and psychology: Beyond heritability. European Psychologists, 6, 229–240.
(1987). Why are children in the same family so different from one another?. Behavioral and Brain Sciences, 10(1), 1–60.
(1980). Behavioral Genetics. New York, NY: Freeman and Co.
(2004). A functional polymorphism in the succinate-semialdehyde dehydrogenase (aldehyde dehydrogenase 5 family, member A1) gene is associated with cognitive ability. Molecular Psychiatry, 9, 582–586.
(2003). Theory and practice in quantitative genetics. Twin Research, 6, 361–376.
(2006). Progress in the molecular-genetic study of intelligence. Current Direction in Psychological Science, 15, 151–155.
(2005). A genowide scan for intelligence identifies quantitative trait loci on 2q and 6p. American Journal of Human Genetics, 77, 318–326.
(2006). Chorion type, birthweight discordance and tooth-size variability in Australian monozygotic twins. Twins Research and Human Genetics, 9, 285–291.
(2007). Neurofibromatosis Type I in genetic counseling practise: Recommendations of the National Society of Genetic Counsellors. Journal of Genetic Counseling, 16, 387–407.
(1962). Parental handling in two strains of mice reared by foster parents. Science, 137, 129–130.
(2005). The equal environments assumption of classical twin studies may not hold. British Journal of Educational Psychology, 75, 339–350.
(2008). Maternal and genetic effects on the acoustic startle reflex and its sensitization in C3H/HeN, DBA/2JHd and NMRI mice following blastocyst transfer. Behavior Genetics, 38, (pp. 596–611). .
(2006). Genetic and environmental influences on social behaviour and health. In , Socioemotional development and health from adolescence to adulthood (pp. 56–75). New York, NY: Cambridge University Press.
(1980). Data from kinships of monozygotic twins indicate maternal effects on verbal intelligence. Nature, 283, 375–377.
(1981). Placentation effects on cognitive resemblance of adult monozygotes. Twin research 3: Intelligence, personality, and development (pp. 35–41). New York, NY: Allen Liss.
(2004). Existe-t-il des gènes du comportement? Paris: Odile Jacob.
(1990). Are intelligence differences hereditarily transmitted?. C.P.C: Cahiers de Psychologie Cognitive European Bulletin of Cognitive Psychology, 10, 555–694.
(1976). Génétique et comportement. Paris: Masson.
(1978). Intelligence : différences individuelles, facteurs génétiques, facteurs d’environnement et interaction entre génotype et environnement. Annales de Biologie Clinique, 36, 101–112.
(2007). From DNA to the mind. EMBO Reports, 8. Science & Society Special Issue S7–S11.
(2005). Attack behaviors in mice: From factorial structure to quantitative trait loci mapping. European Journal of Pharmacology, 526, 172–185.
(in press ). Brain development, genes, epigenetic events and maternal environments. In , Neurobiology of development. Hoboken, NJ: Wiley.2006). Trisomy 21: From chromosomes to mental retardation. Behavior Genetics, 36, 346–354.
(2003). Mitochondrial DNA modifies cognition in interaction with the nuclear genome and age in mice. Nature Genetics, 35, 65–69.
(1994). Enhanced aggressive behavior in mice lacking 5- HT1B receptor. Science, 265, 1875–1878.
(1968). Environmental bias in twin studies. Eugenic Quarterly, 15(1), 34–40.
(2005). The dawn of cognitive genetics? Crucial developmental caveats. Trends in Cognitive Sciences, 3, 126–135.
(2006). Mouse models of cognitive disorders in trisomy 21: A review. Behavior Genetics, 36, 377–386.
(1996). Long term effect of prenatal heterogeneity among monozygotes. CPC Cahiers de Psychology Cognitive Current Psychology of Cognition, 15, 283–308.
(1934). Individual differences. In Comparative psychology, pp. 409–445. Englewood Cliffs, NJ: Prentice-Hall (Reprinted in Behavior-Genetic Analysis, 32–63, by J. Hirch, & T. McGuire, 1982).
(2003). Socioeconomic status modifies heritability of IQ in young children. Psychological Science, 14, 623–628.
(2001). Quantitative trait locus mapping in laboratory mice derived from a replicated selection experiment for open-field activity. Genetics, 158, 1217–1226.
(1989). Genetic and environmental variation in the birth weight of twins. Behavior Genetics, 19, 51–61.
(1971). Attempted replication of, and selective breeding for, instrumental conditioning of Drosophila melanogaster . Animal Behaviour, 19, 454–462.
(