Population prevalence of psychopathology in children and adolescents with intellectual disability: I rationale and methods

Our knowledge of the epidemiology of psychopathology in children and adolescents with intellectual disability (ID) is hampered by a number of factors. These include the relative scarcity of studies of children rather than adults, the study of non-epidemiological samples such as those in institutions or those attending psychiatric clinics, a lack of standardized methods of assessment of psychopathology, studies with numbers too small to provide adequate confidence intervals around identified prevalence rates, insufficient detail concerning symptoms or syndromes as well as disorder, and a lack of consistent data concerning the effects of basic demographic variables such as age, sex and IQ. Despite these limitations, it is clear that psychopathology is several times more prevalent in children and adolescents with ID than in those without this disability. This paper reviews findings from previous studies and describes the methodology of a new study using the Developmental Behaviour Checklist.     

High prevalence of obesity in ambulatory children and adolescents with intellectual disability

Background   Obesity prevalence is unusually high among adults with intellectual disability (ID). There is limited and conflicting evidence on obesity prevalence among ambulatory children and adolescents with ID. The present study aimed to estimate obesity prevalence in this group and to compare with population prevalence.
Methods   Survey of nine schools ( n  = 206, 150 boys) for ambulatory children and adolescents with mild-moderate ID in Scotland in 2007. Obesity was defined as measured body mass index (BMI) at or above the 95th percentile relative to UK 1990 reference data, and using the international definition based on BMI. Obesity prevalence observed was compared against Scottish population data on obesity prevalence from the most recent nationally representative survey.
Results   Obesity prevalence (at or above 95th percentile for BMI) was 36%, and was significantly higher among those attending secondary schools compared with primary schools ( P  < 0.01). Prevalence of obesity was significantly higher than in the general paediatric population in both boys and girls ( P  < 0.01).
Conclusions   The present study suggests that that obesity may be very prevalent among ambulatory children and adolescents with ID, and that increased obesity risk may begin in childhood.     

Assessing emotional and behavioral problems in children with intellectual disability: revisiting the factor structure of the developmental behavior checklist

The objective of the reported study was to reassess the factor structure of the Developmental Behaviour Checklist (DBC) in a large cross-cultural sample representing all levels of intellectual disability. Parent and teacher DBC ratings on a combined sample of 1536 Dutch and Australian children and adolescents (ages 3–22) with mild to profound intellectual disability were used. Principal components analyses produced five subscales: Disruptive/Antisocial, Self-Absorbed, Communication Disturbance, Anxiety, and Social Relating, explaining 43.7% of the total variance. Internal consistencies of these subscales ranged from .66 to .91. The revised factor structure of the DBC appears to be an improved and useful tool for assessing emotional and behavioral problems in children with intellectual disabilities.     

Socioeconomic status and children with intellectual disability in China

Background Intellectual disability (ID) accounts for 70% of all disabilities among children in China's Second National Sampling Survey on Disability. Although studies have shown a relationship between social class and ID in children, none have investigated the association of socioeconomic variables in Chinese children with mild or severe ID. Methods Data for children aged 0–6 years with and without ID were abstracted from the Second National Sampling Survey on Disability in China, conducted in 2006. Crude odds ratios showed the effect of sociodemographic factors on mild and severe ID. Adjusted odds ratios (OR_a) (95% confidence intervals) estimated the independent effects of these factors. Results For both mild and severe ID, risk of having ID increased with male sex, birth to a woman aged 35 years and older, lower maternal education, mother's older age at delivery, lower income and rural residence. After age, gender and parent disability were controlled, mothers aged 35 years and older were more likely to have a child with ID: mild ID, OR_a 1.47 (1.15–1.88); severe ID, OR_a 1.32 (1.00–1.73). There was an approximate increasing monotonic risk of severe ID with increasing socioeconomic disadvantage: lowest income, OR_a 3.00 (2.19–4.12); low income, OR_a 2.28 (1.63–3.19); lower middle income, OR_a 1.72 (1.27–2.33); middle income, OR_a 1.73 (1.28–2.36). Conclusions There is a significant relationship between sociodemographic factors and ID. Similar patterns were found for both mild and severe ID. Recommendations are given for preventing ID in Chinese children.     

Risk factors for psychopathology in children with intellectual disability: a prospective longitudinal population-based study

Background This study examined risk factors for the development of psychopathology in children with intellectual disability (ID) in the developmental, biological, family and social‐ecological domains. Methods A population sample of 968 children, aged 6–18, enrolled in special schools in the Netherlands for educable and trainable ID were assessed at Time 1. A random 58% were re‐contacted about 1 year later, resulting in a sample of 474 at Time 2. Results Psychopathology was highly consistent over 1 year. Risk factors jointly accounted for significant, but small, portions of the variance in development of psychopathology. Child physical symptoms, family dysfunction and previous parental mental health treatment reported at Time 1 were uniquely associated with new psychopathology at Time 2. Conclusions Prevention and early intervention research to find ways to reduce the incidence of psychopathology, possibly targeting family functioning, appear important.     

Early-onset psychosis in youth with intellectual disability

Background Accurate diagnosis of psychotic disorders may be very difficult in youth with intellectual disabilities. Method The authors reviewed the assessment, treatment and follow‐up of 21 youths with ID referred because of early onset of psychotic symptoms. Results Just over one half of the patients had a diagnosis of schizophrenia or schizoaffective disorder. One third of the sample carried the diagnosis of psychosis NOS (not otherwise specified). After careful review, five out of seven of these psychotic‐like cases were assessed as non‐psychotic. Patients with Psychosis NOS associated with moderate or severe ID had the worst outcome. Conclusion This clinical review provides important information about the identification, diagnosis and outcome of psychotic symptoms in youth with low verbal abilities.     

Self-reported anti-social behaviour: prevalence and risk factors amongst adolescents with and without intellectual disability

Background Research has suggested increased risk of anti-social behaviour amongst individuals with intellectual disability (ID). Methods This study reports the results of a secondary analysis of data relating to self-reported anti-social behaviour, obtained from the 1999 Office for National Statistics (ONS) study of the mental health of children and adolescents in Great Britain. Self-report data from 4174 adolescents was available. Within this group, a sub-group of 98 adolescents with ID was identified. Data covered a variety of sub-types of anti-social behaviour. Results Comparisons of individuals with ID and those without ID indicated a significantly higher prevalence of a number of types of self-reported anti-social behaviour in the ID sample. Further analyses indicated however, that these between group differences were accounted for by the higher rates of social deprivation and child mental health problems among the ID sample. Conclusions Rather than ID per se being associated with increased rates of anti-social behaviour, adolescents with ID may be more likely to experience risk factors (lower socio-economic status and mental health problems) known to be associated with anti-social behaviour. The clinical implications of this and possible future directions for research are discussed.     

Psychometric properties of the revised Developmental Behaviour Checklist scales in Dutch children with intellectual disability

The present study assessed the reliability and validity of the revised scales of the Developmental Behaviour Checklist (DBC) in a Dutch sample of children with intellectual disability (ID). The psychometric properties of the parent and teacher versions of the DBC were assessed in various subsamples derived from a sample of 1057 Dutch children (age range = 6–18 years) with ID or borderline intellectual functioning. Good test–retest reliability was shown both for the parent and teacher versions. Moderate inter‐parent agreement and high one‐year stability was found for the scale scores. Construct validity was satisfactory, although limited by high informant variance. The DBC scales showed good criterion‐related validity, as indicated by significant mean differences between referred and non‐referred children, and between children with and without a corresponding DSM‐IV diagnosis. The reliability and validity of the revised DBC scales are satisfactory, and the checklist is recommended for clinical and research purposes.     

Antipsychotic medication, psychiatric diagnosis and children with intellectual disability: a 12-year follow-up study

This study is a follow-up to an original survey carried out in the early 1980s of all children with an identified intellectual disability in Cornwall, England. The purpose of this second study was to review the use of antipsychotic medication in these children and to relate it to their various diagnoses. This is a relatively under-researched area, and the few comparable studies in children have not been designed to specify diagnoses, psychiatric or otherwise. A positive relationship between the diagnosis of autistic spectrum disorders in children and the use of antipsychotic medication was one of the important findings which emerged from the research. The possible reasons for this association are discussed.     

Age-related fractures in people with intellectual disability and epilepsy

The present paper describes age-related fractures in 68 people with intellectual disability and epilepsy (39 females and 29 males). A higher incidence of fractures in epileptic subjects (269%) was noted when they were compared with non-epileptic patients (15%). In the sample of 263 epileptics (121 females and 142 males), a higher number of females (32%) sustained fractures than their male counterparts (20%). The peak period of all fractures is between 40 and 49 years of age. The highest incidence of fractures in females occurred during the periods from 10 to 19 and 40 to 49 years, while the peak was between 30 and 39 years for males. The causes of fractures and preventative measures are discussed, and further avenues for research are indicated.     

Mental health problems in children with intellectual disability: use of the Strengths and Difficulties Questionnaire

Background The assessment of mental health problems in children with intellectual disability (ID) mostly occurs by filling out long questionnaires that are not always validated for children without ID. The aim of this study is to assess the differences in mental health problems between children with ID and without ID, using a short questionnaire, the Strengths and Difficulties Questionnaire (SDQ). Methods We studied 260 children (6–12 years) selected from special education schools for trainable children (response: 57%). Parents completed the extended Dutch version of the SDQ, questions on background characteristics and on the care provided. A non‐ID control group of 707 children (response: 87%) was included to compare mental health problems. Results In total, 60.9% of children with ID had an elevated score on the SDQ, compared with 9.8% of children without ID. Only 45% of the children with ID and an elevated SDQ score had visited a healthcare professional for these problems in the last 6 months. Discussion The SDQ or an adapted version could contribute to the early identification of mental health problems in children with ID. Further research is needed to confirm the validity of the SDQ when used in a sample of children with ID.     

Association between waist circumference and hypertension in children and adolescents with intellectual disabilities

Background: The prevalence of abdominal obesity (AO) is high in individuals with intellectual disability (ID). The aim of this study was to assess the prevalence of hypertension (HPT) in students with ID with different distributions of adipose tissue.

Method: Study involved 568 participants with ID. AO was assessed on the basis of waist circumference (WC) measurements.

Results: The risk of HPT was more than threefold higher in individuals with AO (OR?=?3.38) than in the subjects with normal WC. Correlation between the prevalence of AO and HPT was observed in girls and individuals with mild levels of ID (OR = 6.07 and 7.67 respectively). The prevalence of HPT increases sharply in girls whose WC is greater than or equal to the 90 percentile, and in boys when it exceeds the 75th percentile.

Conclusion: An association between WC and HPT was observed in abdominally obese students with ID.     

Ethnic variation in service utilisation among children with intellectual disability

Background   This study examined whether service utilisation among children with intellectual disability (ID) varied by ethnic cultural group.
Method   Survey carried out in four special schools in London. Information was provided by school teachers using case files, and 242 children aged 7 to 17 years with mild and moderate ID were identified. Ethnic categories were derived from self-reported main categories. Service utilisation categorised as use of: child and adolescent mental health services (CAMHS), social services, physical health and education services.
Results   Child and adolescent mental health services uptake was lower for South Asians than for White British ( P  = 0.0487). There were statistically significant differences among ethnic groups for community-based social services uptake (being the highest for the Black groups and the lowest for South Asians, P  = 0.015) and respite care uptake (being the highest for the Black and White European groups and the lowest for South Asians, P  = 0.009). In regression analysis family structure predicted CAMHS service utilisation and social service community support. Ethnicity predicted use of respite care.
Conclusions   Significant ethnic differences in service utilisation among children with ID were found for both CAMHS and social service contact. There was particularly low service use for the South Asian group. These differences might arise because of differences in family organisation, as more South Asian children lived in two-parent families, which may have been better able to provide care than single-parent families. Other factors such as variation in parental belief systems and variation in psychopathology may be relevant. Implications are discussed.     

Old World—new territory: European perspectives on intellectual disability

People with intellectual disability share the mixed fortunes of the diverse countries in that they live, as well as the social and political changes that mark life in Europe at the close of the twentieth century. The European Union exerts its influence through common policies and centrally funded initiatives which promote the social and vocational integration of people with intellectual disabilities. At the same time, many countries in Central and Eastern Europe are building a new and as-yet untested social order. This paper outlines the distinctive features of European identity. Some of the gains already achieved on behalf of Europeans with intellectual disability are presented, as well as some of the problems which continue to threaten their well-being and inclusion. It is suggested that partnerships between countries and regions can help to chart new territory for citizens of the Old World.     

Sexual abuse in children and adolescents with intellectual disability

The present authors conducted a study of the occurrence of victimization and the perpetration of sexual abuse among 43 in‐patients with intellectual disability aged between 9 and 21 years who were admitted to a child and adolescent psychiatric in‐patient department over a period of 5 years. A retrospective case‐note review was employed that explored the nature and severity of abuse in relation to the age, gender and level of disability. The prevalence of abuse or abusive behaviour, i.e. 14% of 300 admissions, did not change over time. In 13 out of the 43 cases, the issue of sexual abuse was identified after admission. Victimization alone occurred in 21 cases, perpetration alone in six cases, and both victimization and perpetration in 16 cases. Fifty per cent of the victims had been abused by a member of their close or extended family. Most cases (62%) were adolescents. There was only one instance of a victim being abused by a female. However, there were five girls who were perpetrators, all of whom had previously been victims. By contrast, 11 out of the 17 male perpetrators had been victims. Despite difficulties of disclosure, it was possible to establish that severely disabled patients had suffered sexual abuse. The present data support theories which (1) recognize gender differences in sexual abuse patterns and (2) have a developmental perspective, incorporating the influence of adolescence.     

Behavioural and emotional problems in children with intellectual disability attending special schools in Cape Town, South Africa

A sample of 355 children with intellectual disability (ID) attending special schools in Cape Town, South Africa, were assessed on the Developmental Behavioural Checklist – Teacher Version (DBC‐T). A prevalence rate of 31% for psychopathology was found. Boys manifested more behaviour problems than girls, especially in relation to disruptive, self‐absorbed and antisocial behaviours. Children with severe and profound levels of ID showed more behavioural difficulties than those in the mild and moderate categories. Specific behaviour problems were self‐absorbed and autistic behaviours in children with profound ID, communication problems and anxiety in those with severe ID and antisocial behaviour in children with mild ID. Epilepsy, but not cerebral palsy was associated with higher total behaviour scores. Ambulant children were more disruptive and antisocial, while non‐ambulant children were more anxious. Non‐verbal children had higher scores on all of the subscales except for disruptive behaviour.     

Classification, prevalence, prevention and rehabilitation of intellectual disability: an overview of research in the People's Republic of China

The People's Republic of China is a developing country with all the problems and challenges that face such countries all over the world. Progress has been hampered by scarcity of resources, and a lack of relevant information and appropriate skills, as well as by the stigma traditionally attached to people with intellectual disability. The present rapid economic development has made possible further improvement and expansion of educational opportunities, and health and rehabilitation services. According to a recent census and sample surveys conducted in the People's Republic of China, the overall prevalence rate of people with disabilities was estimated to 4.9%. Thus, China has more individuals with disabilities than any other country in the world. According to these figures, the prevalence of intellectual disability in the population is × I %. For children younger than 14 years of age, the prevalence is around 2%, which accounts for 66% of all handicapped children, making it the most frequent childhood disability. Today, the existing medical facilities, and educational and social welfare organizations cannot meet the tremendous need of care and services. The problems of the large number of disabled children and adults are a major challenge for contemporary Chinese society. This paper is devoted to research pertinent to intellectual disability in China. With a few exceptions, only publications in the English language were included in this review, which makes the overview selective rather than comprehensive. Publications on classification systems and diagnostic criteria, screening methods and assessment instruments, prevalence rates, aetiology and risk factors, prevention and intervention efforts, special education, and families with children with intellectual disability are presented.     

Cause-specific mortality of people with intellectual disability in a population-based, 35-year follow-up study

The aim of the present study was to investigate cause‐specific mortality in people with intellectual disability (ID). It was based on a 35‐year follow‐up study of a nation‐wide population of 2369 subjects aged between 2 and 97 years. The 1095 deceased people had accumulated 64 539 person‐years. The research took the form of a prospective cohort study with mortality follow‐up. Observed and expected deaths were calculated as standardized mortality ratios using the Finnish general population as the reference. Cause‐specific mortality ratios were calculated by the level of ID, sex and age. The three most common causes of death were cardiovascular diseases, respiratory diseases and neoplasms. Disease mortality was high up to 40 years of age, but did not increase thereafter. The difference between sexes in cause‐specific mortality was smaller than in the general population. Cause‐specific mortality differed significantly from the general population, with reduced mortality from neoplasms and external causes, but ageing individuals with mild ID had similar mortality patterns to the general population. The disparities in the cause‐specific mortality between younger people with ID and the general population fade with advancing age, producing similar health risks. In preventative work, special attention should focus on common diseases and accidents in the community.     

The development of a new measure for the assessment of psychopathology in adults with intellectual disability

Background   People with intellectual disability (ID) and untreated psychiatric disorder lead unnecessarily difficult and unhappy lives. The prevalence of mental illness in children and adults with ID is greater than that found in the general population. A carer-completed checklist of psychopathology that could be used with both children and adults would help identify those individuals with ID most likely to have a mental health problem, help ensure that they receive the limited services that are usually available and also assist the process of clinical assessment, diagnosis and management.
Method   This research aimed to develop a reliable and valid carer-completed checklist of psychopathology for adults with ID by redeveloping an existing measure for children with ID, the Developmental Behaviour Checklist (DBC-P). The new checklist, The Developmental Behaviour Checklist for Adults (DBC-A) was devised by changing, deleting and adding to DBC-P items. Reliability studies were conducted with paid and family carers, and DBC-A scores were compared with the results from two other measures of psychopathology.
Results   One DBC-P item was deleted, seven items changed and 12 items added. The psychometric properties of this new checklist, the DBC for Adults with ID (DBC-A), were investigated and found to be satisfactory. Intraclass correlations for test-retest and inter-rater reliability ranged from 0.72 to 0.85, and concurrent validity with two measures of emotional and behavioural disturbance was satisfactory.
Conclusions   The carer-completed DBC-A provides a broad and comprehensive survey of the emotional and behavioural problems of adults with ID. It has satisfactory psychometric properties and therefore can be used with confidence in clinical, research and service settings, and its development allows continuous assessment of psychopathology across the lifespan for all people with ID.