Introduction
The term ‘behavioural phenotype’ refers to those aspects of an individual’s development, psychological state and behaviour which can be attributed to the presence of a specific genetic or other biological anomaly. It covers vulnerability to psychiatric and psychological disturbance as well as cognitive (intellectual) abilities. The emphasis is on a predisposition towards certain intellectual, emotional, behavioural and temperamental tendencies. Not all individuals with the same genetic anomaly will show a particular tendency, and not all of those that do will show it to the same degree. Such behaviours are important in that they may provide clues to the presence of an underlying genetic cause for the individual’s developmental and behavioural difficulties. They may also indicate what combinations of interventions are likely to be most effective.
Acknowledgement of a biological basis to certain behavioural traits does not reduce the importance of psychological and social factors which can have an added effect, for better or for worse, on the biologically caused tendencies. It is also important to note that psychological, educational and social interventions are often highly effective. Nonetheless, accepting that such problems are primarily caused by genetic, as opposed to family or other social factors, can be an enormous relief for parents who may be feeling guilty, believing they have caused their son’s or daughter’s difficulties. Such a diagnosis is important for a number of other reasons as well:
- the individual’s and family’s basic human rights to know of underlying causes of developmental and psychological difficulties which may affect the ability to lead a full and satisfying life without assistance
- the potential to receive information on likely developmental progress and challenges (including behavioural ones) the individual is likely to experience
- facilitation of the grief process relating to having a disability, or having a family member who has a disability or genetic disorder
- assistance in focusing on the future and developing suitable plans
- awareness of the need for family genetic counselling
- potential to be given information and get in touch with appropriate support groups or other parents.
The first use of the behavioural phenotype concept was by Langdon Down in his original description of individuals with Down’s syndrome. He described a characteristic profile of personality traits. These included strong powers of imitation, a lively sense of humour and the ridiculous, obstinacy (stubbornness) and amiability (friendliness and agreeability). His proposal has generated substantial debate over the years, not least because of the wide variability in personality profiles witnessed in people who have Down’s syndrome, just as in the general population. However, substantial research now supports the notion that there is a greater similarity personality- and temperament-wise between people with Down’s syndrome than would be expected by chance. Research has also confirmed the increased risk amongst people with Down’s syndrome of developing Alzheimer’s Presenile Dementia and depression (see entry Depression in Children and Young People). Two common causes of challenging behaviour (see entry) in people with intellectual disability. Conversely, young people with Down’s syndrome show relatively low rates of the two major neurodevelopmental disorders of childhood, namely autism spectrum conditions (see entry Autism Spectrum disorders, including Asperger syndrome) and Attention Deficit Hyperactivity disorder (ADHD). Note that people with Down’s syndrome can and do get both these conditions. On such occasions, the problems are often overlooked with subsequent failure to institute a suitable learning and therapeutic programme. This issue is one of ‘diagnostic overshadowing’, meaning that all the individual’s problems tend to be attributed to their having Down’s syndrome (or intellectual disability) rather than other diagnoses. As well as usually causing intellectual disability, young adults with Down’s syndrome appear to be more at risk of experiencing low mood and depression than others of similar age. It is important that this is identified promptly and accurately so that it can be treated effectively.
The first modern use of the term behavioural phenotype was in relation to young people with the X-linked condition Lesch Nyhan syndrome. This rare condition is transmitted on the X chromosome, so all known sufferers are males. Individuals with Lesch Nyhan syndrome often seem normal at birth but later develop marked limb movement difficulties as well as severe self-mutilation, including knuckle gnawing and lip biting. This compulsive behaviour is a major cause of ill health and personal distress for the individuals concerned and their carers, yet remains extremely resistant to psychological and medical treatments.
Much research has confirmed that the frequency, duration and intensity of self-injurious behaviour is closely linked to personal experiences, how one has been treated by others and how the person’s surroundings are structured and organised. However, the likelihood of self-injury, its nature, or type, appear to be driven substantially by the underlying genetic cause of the intellectual disability. There are many examples of this in addition to those given above. Individuals with Cornelia de Lange syndrome are prone to lip biting. People with Prader-Willi syndrome overeat unless helped to resist the overwhelming urges. Therefore, they are at high risk of serious obesity with all its associated health problems including diabetes mellitus. Those with fragile X syndrome often bite their hands (usually at the base of the thumb) in response to anxiety or excitement. Individuals with Smith-Magenis syndrome frequently head-bang and pick and pull at their finger and toenails. They have also been reported as being at an increased risk of inserting objects into their bodily orifices (eg nose, ears, mouth and anus). Individuals with the rare condition hypomelanosis of Ito often display self-injury in the form of wrist and knuckle biting. However, self-injury may be explicable largely in terms of the individual’s social and environmental circumstances. For example, people with another rare condition, Aicardi syndrome, do head bang a lot, but probably no more than expected for their general levels of developmental ability and social circumstances.
When considering behavioural phenotypes it is useful to separate psychological processes which may be involved into several categories:
- intellectual strengths and needs
- speech and language skills
- concentration skills, impulse control and freedom from distractibility
- social functioning
- self-injurious tendencies
- other psychological difficulties such as obsessive-compulsive tendencies (see entry Obsessive Compulsive disorder), anxieties, mood disorders and aggression
- interaction with physical features that affect behaviour, for example enlarged tongue affecting language in people with Down’s syndrome, joint laxity predisposing to clumsiness in people with fragile X syndrome, and oesophageal reflux causing distressing heartburn in individuals with Cornelia de Lange syndrome.
Intellectual strengths and needs
Some genetic conditions have a specific effect on the likely level of intelligence. They may even cause a particular pattern of strengths and needs. Usually an underlying specific genetic cause for a person’s intellectual disability is not discovered despite intensive investigation. The most common known genetic cause of intellectual disability is Down’s syndrome. Most people with Down’s syndrome have an extra chromosome 21 that has occurred as a new mutation rather than having been inherited. There is also a rare cause of Down’s syndrome known as a translocation and this form is inherited. People with Down’s syndrome have very variable intellectual abilities, usually in the mild-to-moderate learning disability range. Their social functioning is typically higher than their cognitive (intellectual) abilities. The most common inherited cause of intellectual disability is fragile X syndrome. People with fragile X syndrome experience very variable intellectual abilities, but these are usually in the mild-to-moderate intellectual disability range. They often have strong language skills and need assistance in relation to their numeracy and visuospatial (relating to visual perception of spatial relationships among objects) abilities. In addition, their rate of intellectual growth may slow down towards adolescence because of particular difficulties with dealing with ‘sequential information processing’ (sequences of information). The genetics of fragile X syndrome is extremely complicated. A few boys and men may have quite a substantial genetic abnormality, yet appear relatively unaffected. Conversely, as many as a third of female carriers experience developmental and behavioural difficulties. These may be extreme, for example severe learning disability and autism. Psychological issues may be very subtle, showing themselves as specific difficulties with mathematics, or problems in organising information in one’s mind and planning ahead. Children with velo-cardio-facial (VCF) syndrome, caused by a microdeletion on the long arm of chromosome 22, also typically attain higher verbal than performance IQ scores, as do girls and women with Turner syndrome, who have just the one X chromosome. In contrast, individuals with Klinefelter syndrome, who have three sex chromosomes (one Y and two Xs) have problems more with language and other verbal tasks. Most individuals with [Williams syndrome][17] have a learning disability and need special schooling. They too have particular difficulties with visuospatial and motor skills, yet have strikingly good expressive language, even though their comprehension lags behind somewhat.
Speech and language skills
Speech and language abilities and styles can be surprisingly affected by having a particular genetic syndrome. People with fragile X syndrome often have a jocular style to their conversation with ‘litanic’ (up and down) swings of pitch as well as perseverations (going on and on about the same thing) and repetitions. They also show language features suggestive of autism spectrum conditions, such as echolalia (repetition of phrases) even in the presence of a friendly and socially aware personality. Williams syndrome characteristically produces superficially grammatically correct, complex and fluent language that may lead to overestimation of general intellectual ability. In some conditions, such as [Angelman syndrome][18] caused by problems on chromosome 15, verbal communication is usually absent. In others, such as VCF syndrome, there is an early onset of receptive and expressive language impairment.
Attentional skills and overactivity
The association of high activity levels with inattentiveness, restlessness, fidgetiness, impulsive tendencies and marked distractibility is well recognised. Such features are common in people who have a learning disability and often reflect their general developmental level. Occasionally, they may be indicative of a specific developmental delay as in ADHD. Many genetic conditions seem to predispose to such problems – to the extent that it is tempting to speculate on a general, non-specific genetic predisposition. However, some genetic syndromes have been shown to have a particular association with these problems. These include fragile X syndrome, tuberous sclerosis (see entry Tuberous Sclerosis Complex), Williams syndrome, Cornelia de Lange syndrome, Sotos syndrome, Sanfilippo syndrome (see Mucopolysaccharide diseases and Associated diseases), Marfan syndrome, Smith-Magenis syndrome and Turner syndrome. In some instances, the problem is more one of inattentiveness rather than overactivity, as in Turner’s syndrome. Gross motor overactivity may be the major concern as in Smith-Magenis syndrome and Tuberous Sclerosis. There is sometimes evidence for at least some of the above behavioural difficulties to be far more severe than expected for the individuals’ ages and general levels of developmental ability. For example, boys with fragile X syndrome are usually more inattentive, restless and fidgety than their learning disabled peers, even though their activity levels may be similar. Furthermore, boys with fragile X syndrome do not seem to automatically grow out of these problems, unlike many individuals without genetic anomalies or learning difficulties. Overactivity, poor concentration and distractibility are also common in Williams syndrome, and attentional deficits and hyperactivity have been reported as common in Sotos syndrome and VCF syndrome. Restlessness, hyperactivity and inattentiveness may develop after three or four years of life, as in Sanfilippo syndrome.
Social functioning
The ability and drive to relate to other people, to have some idea of their needs and how they are feeling, and to be able to let others know one’s own thoughts and feelings are crucial developmental skills. The combination of multiple qualitative impairments in social functioning with language difficulties, poor imagination skills and marked obsessional tendencies is consistent with a diagnosis of autistic spectrum disorder. These impairments are also known to be associated with a learning disability. Over two thirds of people with autism have a learning disability as well.
As above, the presence of autistic features in people with so many different genetic anomalies suggests a general vulnerability. Again, however, certain genetic syndromes do seem to have a particular association, and even sometimes a strikingly characteristic profile of ‘autistic-like’ features. People with fragile X syndrome often display shyness and social anxiety, an aversion to direct eye contact, delayed imaginary (make-believe) play, echolalia and repetitive speech and self-injury in the form of hand biting, as well as some repetitive activities, in particular hand flapping. There is an increased rate of autism in fragile X syndrome, but the profile of autistic-like features is often seen even in those without autism. There is also good evidence that autism spectrum disorders are unusually common in Tuberous Sclerosis and that they can not be explained by the presence of epilepsy, or the associated learning disability. Conversely, autism may be surprisingly rare, as in Down’s syndrome. Over-sociability may be a problem as in Williams syndrome. Individuals may be very chatty with a particularly well-developed social use of language. They are often outgoing, socially disinhibited and excessively affectionate, yet often still have great problems making friends with others of similar age. Social impairments are frequent in girls with Turner syndrome, where it has been proposed that the risk of autistic disorders is dependent on which parent they have inherited their single X chromosome from.
Other psychological difficulties
Common childhood difficulties may be associated with particular genetic conditions. For example, people with Down’s syndrome and Prader-Willi syndrome are prone to sleep apnoea (breathing difficulties while sleeping). This may contribute to excessive daytime drowsiness. People with Smith-Magenis syndrome and Sotos syndrome are also prone to severe sleep difficulties. In addition, people with Sotos syndrome are vulnerable to frequent severe tantrums, as are those with XYY syndrome, who also show an increased rate of conduct disorders. Some behaviours may be quite unusual, such as the paroxysmal (sudden excessive) laughter in Angelman syndrome, spasmodic upper body squeeze (‘self-hugging’) in Smith-Magenis syndrome and the midline hand wringing and hyperventilation (over breathing) in Rett syndrome.
Other biological causes of behavioural difficulties
It is not only genetic problems that can create patterns of behavioural difficulty. Infections, particularly before birth or early in life can cause behavioural difficulties. For example, congenital rubella or German measles is a well established cause of autism, as well as severe learning disability and visual and hearing problems. Obsessive compulsive disorder may result from infection with the streptococcus bacterium, paediatric autoimmune neurodevelopmental disorder associated with streptococcus (PANDAS). Fetal alcohol spectrum disorders is a very common cause of diminished intellectual ability, expressive and receptive language problems, irritability, hyperactivity and difficulty perceiving social cues. Hydrocephalus can be associated with problems sequencing information and impulse control.
Helping people who have a genetically determined behavioural phenotype and their families
Knowledge and awareness of behavioural phenotypes is not just of use diagnostically. It is also critical in the early development of a suitable support package covering medical, psychological, educational and social needs. For example, people with Prader-Willi syndrome need help from an early age to acquire healthy eating habits and routines. The family should be fully informed and aware of the condition and its consequences and should, where appropriate, receive genetic counselling. They should have attention paid to the suitability of their living environment and whether they are receiving all appropriate benefits. They should also be offered the opportunity to link with appropriate support groups and other parents.
The individual concerned should receive a thorough educational evaluation incorporating knowledge of the genetic condition along with the person’s unique profile of developmental strengths and needs. Careful consideration is required regarding educational placement and curriculum, including essential therapeutic components such as speech and language work. Help should be available for associated challenging behaviours and the needs of siblings. Early intervention packages such as support from a Portage worker should be in place. Occasionally the careful use of medication in addition to the above may be helpful for specific behavioural problems.
References
Bernard S, Turk, J. Developing mental health services for children & adolescents with learning disabilities: a toolkit for clinicians. 2009; London, UK: Royal College of Psychiatrists.
Courtenay K, Soni S, Strydom A, Turk J. Behavioural phenotypes and mental disorders. Psychiatry. 2009;8:391–7.
Mijovic A, Turk J. Behavioral phenotypes and child and adolescent mental health. Current Medical Literature Pediatrics. 2008;21:1–9.
O’Brien G. Behavioural Phenotypes in Clinical Practice. 2002; London, UK: MacKeith Press.
Turk J, Graham PJ, Verhulst F. Child & Adolescent Psychiatry: A Developmental Approach (4th Edition). 2007; Oxford, UK:Oxford University Press.
Turk J. Behavioural phenotypes in relation to ADHD. ADHD in Practice. 2009;1:8–12.
Turk J. Behavioural phenotypes: Their applicability to children and young people who have intellectual disability. Advances in Mental Health in Learning Disabilities. 2007;1: 4–13.
Medical text written October 2000 by Professor J Turk. Last updated November 2010 by Professor J Turk, Professor of Developmental Psychiatry, St George’s and the Institute of Psychiatry, University of London and Consultant Child & Adolescent Neuropsychiatrist, Child & Adolescent Mental Health Developmental Neuropsychiatry Services, South London & Maudsley Foundation NHS Trust, London, UK.
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