Twin studies demonstrate the importance of genes and environment in the aetiology of childhood psychiatric and neurodevelopmental disorders. Advances in molecular genetics enable the identification of genes involved in complex disorders and enable the study of molecular mechanisms and gene--environment interactions.
To review the role of molecular genetics studies in childhood behavioural and developmental traits.
Molecular approaches to complex disorders are reviewed, with examples from autism, reading disability and attention-deficit hyperactivity disorder (ADHD).
The most robust finding in ADHD is the association of a variable number tandem repeat polymorphism in exon 3 of the DRD4 gene. Other replicated associations with ADHD are outlined in the text. In autism, there is a replicated linkage finding on chromosome 7. Linkage studies in reading disability have confirmed a locus on chromosome 6 and strongly suggest one on chromosome 15.
In the next 5--0 years susceptibility genes for these disorders will be established. Describing their relationship to biological and behavioural function will be a far greater challenge.
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"Traditional molecular genetic techniques have been supplemented by quantitative trait loci (QTL) mapping, an approach that is useful when traits (such as hyperactivity) are continuously distributed in the population (Plomin, 1999). Molecular genetic studies have shown associations between ADHD and dopamine receptor genes and the dopamine transporter DAT 1 (Asherson & Curran, 2001; Barr, 2001). An international study is currently under way in the IMAGE project (Asherson et al, 2003). "
[Show abstract][Hide abstract] ABSTRACT: The development of the mammalian brain is both a highly organized and chaotic process that is nothing short of a miracle.
The complexity with which the human brain develops from but a mere plate of ectodermal cells is still not fully understood.
Numerous disorders have their etiology seeded in abnormal development during the prenatal and perinatal stages of central
nervous system (CNS) development. Various signaling molecules and the precisely orchestrated expression and silencing of neural-specific
genes may be disrupted in the CNS development of patients suffering from developmental disorders. In this chapter we present
an overview of the normal neural mechanisms of mammalian brain development and how errors in this process contribute to developmental
disorders. Developmental disorders are defined as those disorders of the CNS that impair normal functioning and development
in early childhood. Developmental pathologies encompass various learning disabilities, dyslexias, dyspraxias, metabolic disorders,
and anatomical abnormalities, including those that may result from teratogen exposure. Developmental disorders may affect
one specific area of development, or may involve numerous areas as in the case of pervasive developmental disorders. More
global developmental disorders result from inherent metabolic abnormalities and more recently described immune mediated mechanisms.