A battle for supremacy between a mother's and father's genes in a developing foetus could explain a spectrum of mental disorders from autism to schizophrenia according to a radical new theory by LSE sociologist Christopher Badcock.
In his new book The Imprinted Brain: How Genes Set the Balance Between Autism and Psychosis, Badcock sets out the hypothesis that a 'win' for the father's genes pushes the developing brain towards the autism spectrum and a 'win' for the mother's pushes it in the direction of psychosis.
Although a child inherits half its DNA from each parent, in normal development a phenomenon called 'genetic imprinting' means that some crucial genes are only expressed if they come from one parent rather than the other. However, if both parent's copies of the gene are either expressed or – conversely – imprinted or silenced this can result in various disorders. These can be seen as beneficial to the parent whose genes 'win'.
For example a gene called IGF2, which codes for a growth hormone, is normally only expressed from the father's gene. If the mother's IGF2 gene is also expressed this results in Beckwith Wiedemann syndrome which results in birth weights that are, on average, 50 per cent above the norm. If the opposite happens and both copies of the gene are silenced, then this causes Silver-Russell syndrome, which results in retarded growth.
From an evolutionary perspective this 'battle' can be seen in terms of the father's gene's being selected to maximize the nutrients they receive during pregnancy and the mother's genes being selected to limit the nutritional costs of pregnancy.
Dr Badcock said: 'Because imprinting is common among genes that drive brain development, it seems to be a reasonable conclusion that this genetic tug-of-war should also affect behaviour, cognition and personality. Autistic children, for example, are notably self-orientated and demanding on their care-givers – usually the mother. So autism may be the result of paternally-biased expression of genes involved with brain development.'
Geneticists have found a region of human chromosome 15, for example, which contains a set of imprinted genes. Children with a paternal bias in gene expression in this area develop Angelman or 'happy puppet' syndrome, which involves hyperactive attention-seeking behaviour in infancy and a very high incidence of autism. Children with a maternal bias in this area develop Prader-Willi syndrome, which features extremely placid, undemanding behaviour in infancy, followed after weaning by compulsive food seeking, which can be seen to reduce the demands on a mother. This is accompanied by rates of psychosis with depression that can approach 100 per cent.
Dr Badcock also argues that most of the most striking symptoms of psychotic illness such as paranoid schizophrenia could be seen as the exact opposite of those found in autism. For example, the autistic inability to monitor and respond to gaze can be seen as the opposite of what happens with paranoia where sufferers think they are being watched or spied upon.
Dr Badcock said: 'The implication is that rather than being totally unconnected, autism and psychosis could represent poles of a spectrum which stretches from the extreme autistic mind-blindness to paranoid hyper-mentalism.'
Given the symmetry of this mentalistic continuum he proposes the existence of 'psychotic savants' who have, for example, extremely well developed people skills which compensate for deficits on the mechanistic front. He says: 'Because the interpersonal skills of psychotic savants are so good, these people don't stand out and haven't been identified as a clinical population in the way that autistic savants have. Because of their skills many of these individuals are probably critically embedded in many social institutions and areas of life where mentalism looms large such as politics, religion, public relations, marketing, fashion, literary and theatrical arts.'
Dr Badcock explains his theory in a video interview
For more information contact LSE Press Office on 020 7955 7060
1 June 2009