Introduction
The term "behavioural phenotype" refers to those aspects of an individual's development 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 concept is not a new one. However it has only recently been widely accepted because of the earlier emphasis on social determinants of psychological state and behaviour. The emphasis is on a predisposition towards certain behavioural tendencies. Not all individuals with the same genetic anomaly will show a particular behaviour, and not all those that do will show it to the same degree. Such behaviours are important in that they may give a clue 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 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 created their son's or daughter's difficulties. Such a diagnosis is important for a number of other reasons as well:
- The individuals' and families' basic human rights to know of underlying causes of developmental and behavioural 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 focussing on the future and developing suitable plans
- Awareness of the need for familial genetic counselling
- Potential to relate to appropriate support groups.
The first use of such a concept was by Langdon Down in his original description of individuals with Down syndrome. He described a characteristic profile of personality traits. These included strong powers of imitation, a lively sense of humour and the ridiculous, obstinacy and amiability. His proposal has received substantial criticism over the years, not least because of the wide variability in personality profiles witnessed in people who have Down syndrome, just as in the general population. But recent research has supported the notion that there is a greater similarity personality and temperament-wise between people with Down syndrome than would be expected by chance. It has also confirmed the increased risk amongst people with Down syndrome of developing Alzheimer's presenile dementia and depression - two common causes of "challenging behaviour" in people with learning disabilities. Conversely, young people with Down syndrome show relatively low rates of the two major neurodevelopmental disorders of childhood, namely Autism Spectrum disorders and Attention Deficit-Hyperactivity Disorder. Note that people with Down syndrome can and do get both these conditions. On such occasions they are often overlooked with subsequent failure to institute a suitable learning programme. The issue is one of "diagnostic overshadowing" where all the individual's problems tend to be attributed to their having Down syndrome (or learning disability) rather than other diagnoses being considered.
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 problem is transmitted on the X chromosome, hence 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-like 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 one's surroundings are structured and organised. However the likelihood of self-injury and its nature or type appear to be driven substantially by the underlying genetic cause of the learning disability. There are many examples of this in addition to the above. Individuals with Cornelia de Lange syndrome are prone to lip biting. People with Prader-Willi syndrome overeat voraciously unless helped to resist the overwhelming urges. They are thus 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, caused by a micro-deletion on the short arm of chromosome 17, frequently head-bang and pick and pull at their finger and toenails. They have also been reported as being at increased risk of inserting objects into their bodily orifices. 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:
- Profile of 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, anxieties, mood disorders and aggression
- Interaction with physical features which affect behaviour, for example enlarged tongue affecting language in people with Down syndrome, joint laxity predisposing to clumsiness in people with Fragile X 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 learning disability is not discovered despite intensive investigation. The most common known genetic cause of learning disability is Down syndrome which has a prevalence of approximately one in 650 individuals. Most people with Down syndrome have an extra chromosome 21 which has occurred as a new mutation rather than having been inherited. There is a rare cause of Down syndrome known as a translocation where a fragment of one chromosome has become detached, and stuck on to another one. This form is inherited. People with Down 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 learning disability is Fragile X syndrome, which occurs in one in 4,000-6,000 individuals. People with Fragile X syndrome experience very variable intellectual abilities but these are usually in the mild to moderate learning disability range. They often have strengths with language skills yet particularly special needs with numeracy and visuo-spatial abilities. In addition, their rate of intellectual growth may slow down towards adolescence because of particular difficulties with dealing with sequences of information ("sequential information processing"). 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 so-called female carriers experience developmental and behavioural difficulties. These may be extreme for example severe learning difficulties and autism. Conversely they 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 velocardiofacial (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 X's) have problems more with language and other verbal tasks. Most individuals with Williams syndrome (idiopathic hypercalcaemia) have learning disability and need special schooling. They too have particular difficulties with visuo-spatial and motor skills yet have strikingly good expressive language even though their comprehension lags somewhat behind.
Speech & 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 up and down ("litanic") swings of pitch and many perseverations (going on and on about the same thing) and repetitions (saying the same word or phrase repeatedly). They also show language features suggestive of Autism Spectrum disorders 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 which may lead to overestimation of general intellectual ability. In some conditions, such as Angelman syndrome (caused by problems on chromosome 15), verbal communication is usually absent. In others such as velocardiofacial syndrome, there is early onset receptive and expressive language impairment.
Attentional Skills & 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 learning disability and often reflect their general developmental level. Occasionally they may be indicative of a specific developmental delay as in Attention Deficit-Hyperactivity Disorder. 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, 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 velocardiofacial 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 conditions are known to be associated with learning disability. Over two thirds of people with autism have learning disabilities 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 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 still frequently have great problems making friends with others of similar age. Social impairments are frequent in girls with Turner's syndrome where it has been proposed that the risk of autistic disorders is dependent on which parent you have inherited your single X chromosome from.
Other Psychological Difficulties
Common childhood difficulties may be associated with particular genetic conditions. For example people with Down syndrome and Prader-Willi syndrome are prone to breathing difficulties while sleeping ("sleep apnoea"). 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's syndrome, "self-hugging" ("spasmodic upper body squeeze") in Smith-Magenis syndrome and the midline hand wringing and hyperventilation (overbreathing) 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 have an influence. For example, congenital rubella (German measles) is a well-established cause of autism as well as severe learning difficulties 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 disorder is a very common cause of diminished intellectual ability, expressive and receptive language problems, irritability, hyperactivity and difficulty perceiving social cues. Hydrocephalus ("water on the brain") 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 aspects. 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 have received genetic counselling. They should have had attention paid to the suitability of their living environment and whether they are receiving all appropriate benefits. They should be offered the opportunity to link with appropriate support groups. 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, familial difficulties coping and the needs of siblings. Early intervention packages such as Portage should be in place. Occasionally the judicious use of medication in addition to the above may be helpful for specific behavioural problems.
REFERENCES
GRAHAM, P.J., TURK, J. & VERHULST, F. (1999) Child Psychiatry: A Developmental Approach. (Pp. 84-109 "Intelligence & Learning Disorders") Oxford: Oxford University Press.
O'BRIEN, G. & YULE, W. (1995) Behavioural Phenotypes. London: MacKeith Press.
O'BRIEN G. (2002) Behavioural Phenotypes in Clinical Practice. London: MacKeith Press.
TURK, J. & SALES, J. (1996) Behavioural Phenotypes and their Relevance to Child Mental Health Professionals. Child Psychology & Psychiatry Review, 1, 4-11.
Medical text written October 2000 by Professor J Turk. Last reviewed July 2004 by Professor J Turk, Professor of Developmental Psychiatry and Consultant Child & Adolescent Psychiatrist, Department of Clinical Developmental Sciences, St. George's Hospital Medical School, London, UK.
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