Sleep problems of children with pervasive developmental disorders: correlation with parental stress

Sleep problems of children with pervasive developmental disorders: correlation with parental stress Sylvia Doo MRCPCH, Child Assessment Service, Department of Health; Yun Kwok Wing* MRCPsych MRCP, Department of Psychiatry, Shatin Hospital, The Chinese University of Hong Kong, Hong Kong SAR, China. *Correspondence to second author at Department of Psychiatry, Room 7011, 7th Floor, Shatin Hospital, Shatin, Hong Kong SAR, China. E-mail: ykwing@cuhk.edu.hk This study aimed to investigate the prevalence of sleep problems in Chinese children with pervasive developmental disorders (PDD) in Hong Kong and their relationship to parental stress. A cross-sectional survey was conducted in six child assessment centres. All parents of the children with PDD completed the Children s Sleep Habits Questionnaire, the Parenting Stress Index Short Form, and questions on sleep practice. A total of 210 out of 250 questionnaires (response rate 84%) were returned. Mean age of the children was 3 years 6 months (SD 1y 4mo; range 2y 7y 7mo; 168 males, 25 females). The prevalence of parent-defined sleep problems in various sleep domains ranged from 9.3 to 45.6%, with 67.9% of children having significant problems in at least one sleep domain. The most common problems reported were bedtime resistance and parasomnias. Similar sleep problems occurred in all the PDD subgroups. The factor most significantly associated with sleep problems was the occurrence of sleep problems before the age of 2 years. The parents of children with PDD with sleep problems experienced a higher level of stress than those whose children had no sleep problems. A high prevalence of significant sleep problems was reported in Chinese children in Hong Kong with PDD. A higher stress level among the parents of those children with PDD with sleep problems suggests the need for systematic early detection and management of sleep problems in children with PDD. See end of paper for list of abbreviations. Sleep disturbances are reported as a common clinical feature among children with pervasive developmental disorders (PDD). Varying prevalence rates of sleep problems (44 83%) were reported among white and Japanese children with PDD (Table I; Taira et al. 1988; Richdale and Prior 1995; Wiggs and Stores 1996, 2004; Patzold et al. 1998; Hering et al. 1999; Schreck and Mulick 2000; Honomichl et al. 2002; Williams et al. 2004; Couturier et al. 2005; Polimeni et al. 2005). In particular, problems with sleep onset, night waking, irregular sleep-wake pattern, early waking, and poor sleep routines were commonly reported (Richdale 1999). The exact aetiology remains unclear but it has been hypothesized that some unique features related to PDD may be directly associated with disturbed sleep (Richdale 1999). Children with a primary social-communication deficit may find it difficult to use social and environmental cues to entrain a circadian rhythm (Johnson 1996, Richdale 1999). Abnormal melatonin regulation, arousal, anxiety level, brain pathology, and genetic factors have also been suggested as contributing factors to the sleep problems (Nir et al. 1995, Richdale 1999, Wimpory et al. 2002). Parents of children with autism suffer more stress than those with children without disabilities or intellectual impairment (Koegel et al. 1992). It has been suggested that sleep problems are an additional burden on families with children with PDD (Johnson 1996, Richdale 1999, Honomichl et al. 2002). Children with sleep problems are more likely to exhibit daytime behaviour problems and/or daytime sleepiness that may interfere with their educational and behavioural development (Wiggs and Stores 1996, Patzold et al. 1998). Cultural factors are known to influence both the type and frequency of sleep problems in children (Owens 2004). In this regard, there is a conspicuous absence of literature on this aspect of Chinese children with PDD. This study aimed to examine the prevalence of sleep problems and to explore the possible relationship between parental stress and sleep problems in Chinese children with PDD. Method This was a cross-sectional survey with a self-administered questionnaire completed by the parents. We recruited a consecutive series of children aged 2 to 8 years from six paediatric developmental assessment clinics in Hong Kong. They were all referred for suspected developmental problems. Clinical diagnoses of autism, PDD not otherwise specified (PDD NOS), or Asperger syndrome were made by paediatricians (including first author, SD) or clinical psychologists based on the Diagnostic and Statistical Manual of Mental Disorders, 4th edn (DSM-IV; American Psychiatric Association 1994) criteria. Developmental quotient (DQ) or intelligence quotient (IQ) was examined using the Griffiths Mental Developmental Scale (Griffiths 1970) or the Hong Kong-Wechsler Intelligence Scale for Children (WISC; adapted from WISC-R; Educational Department and Hong Kong Psychological Society 1981) depending on the children s age. During the 6-month study period, all parents of the children with PDD who had at least a primary education level of literacy and were able to read Chinese were invited to participate in the study. A package containing a letter explaining the objectives of the study, an informed parental consent form, and the questionnaire was given through the assessors after their assessment sessions. Parents who consented to participate in 650 Developmental Medicine & Child Neurology 2006, 48: 650 655

the study completed the questionnaire on their own before leaving the clinics. The ethics committee of the Department of Health of Hong Kong approved the study. MATERIALS The questionnaire included a validated Chinese version of the Children s Sleep Habits Questionnaire (CSHQ; Owens et al. 2000; Tso 2001). The CSHQ has 33 items relating to eight key sleep problem subscales: (1) bedtime resistance; (2) sleep onset delay; (3) sleep duration; (4) sleep anxiety; (5) night waking; (6) parasomnias; (7) sleep disordered breathing; and (8) daytime sleepiness. The parents were asked to recall the sleep behaviour of their children that occurred during a recent typical week. The items were rated on a 3-point scale: usually if the sleep behaviour occurred 5 to 7 times per week, sometimes if it occurred 2 to 4 times per week, and rarely if it occurred 0 to 1 time per week. In addition, the parents were asked to indicate whether or not the sleep behaviour for each item represented a problem. The second section was a validated Chinese version of the Parental Stress Index Short Form (PSI-SF; Tam et al. 1994). This consists of 36 items relating to three factors: (1) parental distress; (2) parent child dysfunctional interaction; and (3) difficult child. Most of the items were on a 5-point scale, ranging from strongly agree to strongly disagree. The final section consisted of 20 questions on sleep habit, environment and demographic data, such as room sharing, noise, sleep routine practice, naps, activities before sleep, and medication. The questions were adapted from previous sleep studies (Tso 2001). Table I: Summary of recent studies on sleep problems in children with pervasive developmental disorders (PDD) Study Tools used Number of cases Response rate, % Age, y:m % of problem sleepers Taira et al. Questionnaire 88: autism Not mentioned Not mentioned 65.1 (1988) (Details not mentioned) Richdale and Prior Sleep diary (Study 1) Not applicable (Study1) (Study 1) (1995) (14d) 12: low function autism; 2:6 19:0 Past problem a IQ <55 Case: 83.3 35: comparison Comparison: 54.3 Current problem a (Study 2) (Study 2) (Study 2) 27: high function autism; 4:0 14:3 Past problem a IQ >55 Case: 70.4 26: comparison Comparison: 61.5 Current problem a Case: 44.4 Comparison: 26.9 Wiggs and Stores Questionnaire-Modified 25: autism 43 5:0 16:0 68 (1996) Simonds and Parraga (209: whole sample b ) (44 for the whole Sleep Questionnaire sample) Patzold et al. Sleep diary 31: autism Not applicable 3:8 14:3 Current problem: (1998) (14d) 7: Asperger Case: 63.2 36: comparison Comparison: 22.9 Hering et al. Questionnaire 22: autism Not applicable 3:0 12:0 54.5 (1999) (details in original paper) 8: comparison and actigraphy Schreck and Mulick Questionnaire-Behaviour 38: autism ~60 5:0 12:0 for the Not mentioned (2000) Evaluation of Disorders 17: PDD whole sample of Sleep (BEDS) (169:total) Honomichl et al. Questionnaire-Children s 100: all 5 entities of <10 2:0 11:0 54 (2002) Sleep Habits Questionnaire PDD included (CSHQ) Wiggs and Stores Questionnaire-Modified 69: autism Not applicable 5:0 16:0 67 (2004) Simonds and Parraga Sleep Questionnaire and actigraph Williams et al. Questionnaire-Modified 210: autism 42 2:0 16:0 Maximum: 53.3 for (2004) sleep survey by Kosair Children s individual items Hospital Sleep Center Overall: not mentioned Polimeni et al. Questionnaires-BEDS and 53: autism Not applicable 2:0 17:0 Autism: 73 (2005) another sleep survey c 52: Asperger Asperger: 73 66: comparison Comparison: 50 Couturier et al. Questionnaire-CSHQ 37: PDDs PDD: 82.2 5:0 12:0 PDD: 78 (2005) 43: comparison Comparison: 55.8 Comparison: 26 a Detailed definition of past and current problem not mentioned in paper; b sample was composed of students with differing developmental problems, all of whom attended a special school; c survey modified from one reported by Robinson and Richdale (2004). Sleep Problems of Children with Pervasive Developmental Disorders Sylvia Doo and Yun Kwok Wing 651

All analyses were carried out using SPSS (version 11.5). The descriptive statistics were expressed as mean and standard deviation (SD). The dependent variables were compared by the χ 2 test, Fisher s exact test, Mann-Whitney U test (for skewed continuous data), or an independent t-test where appropriate. Items that yielded a p value less than 0.15 in the univariate test were further analyzed by multivariate logistic regression or multivariate linear regression with a forward stepwise procedure. A p value less than 0.05 was considered significant. Results A total of 210 out of 250 questionnaires were returned (84% response rate). Of the returned questionnaires, 12 were discarded due to grossly incomplete information. Five children younger than 2 years of age were also excluded as the diagnosis of PDD may be difficult before this age. Altogether, 193 children with PDD were included in the final data analysis. As it was an anonymous study, the characteristics of those that did not respond and their reasons for not responding could not be traced. However, the demographic data of respondents Table II: Number of cases and mean age for each diagnosis and cognitive level Cognitive Level PDD diagnosis Total Autism PDD-NOS/ Asperger syndrome Normal development 26; 3:4 (1:3) 35; 4:0 (1:6) 61 Borderline delay 34; 3:1 (1:0) 37; 3:0 (0:9) 71 Global delay/ 34; 3:10 (1:6) 27; 3:9 (1:7) 61 learning disability Total, n 94 99 193 Values are expressed as number of cases; mean age (SD), y:m. Normal development: developmental quotient (DQ)/intelligence quotient (IQ) >85; Borderline delay: DQ/IQ 70 85; Global delay or learning disability: DQ/IQ <70. PDD, pervasive developmental disorders; PPD-NOS, PDD not otherwise specified. was comparable with the general statistics from the six assessment clinics. The sample consisted of 168 (87%) males and 25 (13%) females. The number of cases and the mean age for each diagnosis and cognitive level is shown in Table II. As there were only two cases of Asperger syndrome, they were grouped with the PDD-NOS for further analysis. The mean age of the children was 3 years 6 months (SD 1y 4mo; range 2y 7y 7mo), while for the males it was 3 years 6 months (SD 1y 4mo) and for the females it was 3 years 6 months (SD 1y 5mo). Children with borderline delay were significantly younger than those with normal development (mean difference 0.64y, 95% confidence interval [CI] 0.10 1.19) and those with learning disability* (mean difference 0.75y, 95% CI 0.21 1.30). The majority (74.6%) of the questionnaires were completed by the mothers. The parental occupations were further grouped according to the economically active status as defined by the Census and Statistics Department of Hong Kong (2001). All the fathers except one (who reported as having a physical disability) were economically active, and 52.8% of the mothers (n=102) were economically inactive as most of them were housewives. Most of the children shared a room with family members, and 61.7% of them slept in the same room as their parents. Regular bedtimes were reported for 151 (78.2%) children. SLEEP PATTERN The mean total sleep duration for the entire sample was 10 hours 50 minutes (SD 1h 24min; range 6h 14h 30min). During weekdays, the mean bedtime and wake time were 22:28 (SD 56min; range 20:00 02:10) and 8:00 (SD 1h; range 05:00 11:00) respectively. During weekends, the mean bedtime and wake time were 22:45 (SD 1h 5min; range 19:15 03:00) and 8:30 (SD 1h 9min; range 05:00 13:00) respectively. Eighty-five out of the 193 children (44%) were reported to wake up during the night and the maximum duration of this period of being awake was reported as 3 hours. There was no significant difference in bedtimes, wake times, naptimes, or sleep duration between sexes or among subtypes of PDD. The children were divided into two groups: aged four or below and aged above four. The younger age group had a longer mean wake time (8.60min vs 5.92min; *North American usage: mental retardation. Table III: Bedtime, sleep time, wake time, homework time, naptime, and total sleep duration in problem and non-problem sleepers Problem sleeper Non-problem sleeper Mann-Whitney U z-score p n Median Mean n Median Mean Bedtime weekday (h:m) 125 22:30 22:34 57 22:30 22:14 2827.50 2.25 0.024 Bedtime weekend (h:m) 124 23:00 22:56 57 22:30 22:30 2846.00 2.12 0.034 Sleep time weekday (hr:min) 123 9:00 9:07 57 9:00 9:31 2877.50 1.97 0.049 Sleep time weekend (hr:min) 122 9:00 9:22 57 10:00 9:43 3003.50 1.49 0.135 Night wakening time (min) 119 1 10.20 60 0 3.19 2729.50 2.78 0.166 Wake time weekday (hr:min) 121 8:00 7:59 58 8:00 7:59 3064.50 1.39 0.166 Wake time weekend (h:m) 120 8:30 8:35 58 8:15 8:20 2874.50 1.90 0.058 Naptime (hr:min) 130 2:00 1:33 62 2:00 1:35 3776.50 0.72 0.470 Total sleep duration weekday (hr:min) 122 10:30 10:41 57 11:00 11:07 2826.00 2.03 0.420 Homework time (hr:min) 130 0:00 0:21 62 0:00 0:22 3727.00 0.92 0.356 n, number of children analyzed; h:m, time on a 24-hour clock; hr, number of hours; min, number of minutes. 652 Developmental Medicine & Child Neurology 2006, 48: 650 655

z= 2.835, p=0.005), a longer mean naptime (1h 49min vs 54min; z= 5.632, p<0.001) and a longer mean total sleep duration (11h 5min vs 10h 15min; z= 3.825, p<0.001). PREVALENCE OF SLEEP PROBLEMS AND SPECIFIC SLEEP BEHAVIOURS The prevalence of problem sleepers (at least one sleep problem behaviour identified by the parents of each child according to the 33 items in the CSHQ) was 67.9% (95% CI 61 75%). The number of perceived problems ranged from 1 to 17. There was no significant difference in sex and age between problem sleepers and non-problem sleepers. The problem sleepers were found to sleep later, and their sleep duration was shorter during weekdays but not during weekends (Table III). The prevalence of individual sleep problem subscales ranged from 9.3 to 45.6%. The problem sleeper group had higher scores on all subscales and a higher total score than the nonproblem sleeper group (Table IV). Bedtime resistance was the most common sleep problem: 44.6% usually (5 7 times per wk) needed the presence of a parent when sleeping and 24.9% were usually afraid of sleeping alone. Parasomnia was the second most common problem, reported by 32.5% of the parents. Frequent (5 7 times per wk) nocturnal bedwetting and teeth grinding occurred among 16.1 and 5.2% of the children respectively; 19.7% of them awoke screaming and sweating, while 19.2% were disturbed by scary dreams more than twice a week. Only 1% of the children were reported to sleepwalk more than twice a week. One-third of the parents (33.7%) reported problems in the sleep anxiety subscale. While 25.4% of the parents reported problems in the sleep duration subscale, only 9.3% of the parents reported that their children usually slept too little. Nearly one-quarter (23.8%) of the parents complained of daytime sleepiness in their children. About 7.8% of the children usually had a hard time getting out of bed, 3.6% took a long time to become alert, 4.2% fell asleep while watching television, and up to 18.1% fell asleep while travelling in cars. Sleep onset delay was perceived as a problem in 21.8% of the children. About 18.7% of the children rarely fell asleep within 20 minutes of going to bed. About a third of the children woke up in the middle of the night more than twice a week. Sleep disordered breathing was the least common problem, reported by only 9.3% of the parents. FACTORS ASSOCIATED WITH SLEEP PROBLEMS Using multivariate logistic regression, the practice of regular sleep time was found to be associated with a lower risk of bedtime resistance (OR [odds ratio]: 0.45, 95% CI 0.22 0.95). The presence of a sleep problem before the age of two was the only significant factor associated with a higher risk of sleep onset delay (OR: 2.38, 95% CI 1.12 5.06), sleep duration (OR: 3.75, 95% CI 1.83 7.67), parasomnias (OR: 2.96, 95% CI 1.49 5.86), and daytime sleepiness (OR: 4.94, 95%CI 2.38 10.25). A sleep problem before the age of 2 years was a significant risk factor for night waking problems (OR: 4.15, 95% CI 1.80 9.54). The age of the child was a protective factor; i.e. the older the child was, the fewer night waking problems the children had. Male sex (OR: 4.72, 95% CI 1.32 16.93) was a significant risk factor for sleep anxiety. Sharing a room with parents or grandparents (OR: 0.11, 95% CI 0.012 0.94) and having a working mother (OR: 0.42, 95% CI 0.21 0.84) were associated with a lower risk of sleep anxiety. When considering the overall problem sleepers, Table IV: Children s Sleep Habits Questionnaire (CSHQ): subscale characteristics Subscales Entire sample PS ( 1 subscale item Mean CSHQ Mann-Whitney (n=193) reported as problem) subscales score test Mean SD Freq. % (95% CI) PS (SD) NPS (SD) z score Bedtime resistance 10.87 2.91 88 45.6 (39 53) 12.2 (2.60) 9.74 (2.68) 5.81 a Sleep onset delay 1.80 0.73 42 21.8 (16 28) 2.45 (0.71) 1.62 (0.63) 6.18 a Sleep duration 4.37 1.39 49 25.4 (19 32) 5.37 (1.27) 4.03 (1.27) 5.89 a Sleep anxiety 6.37 1.84 65 33.7 (27 40) 7.58 (1.50) 5.75 (1.69) 6.77 a Night waking 3.90 1.20 41 21.2 (15 27) 5.32 (1.27) 3.52 (0.85) 8.15 a Parasomnias 9.15 1.89 69 35.8 (29 43) 10.35 (2.04) 8.48 (1.43) 6.51 a Sleep disordered breathing 3.47 0.79 18 9.3 (5 13) 4.83 (1.30) 3.33 (0.56) 6.05 a Daytime sleepiness 11.22 2.48 46 23.8 (18 30) 12.67 (2.63) 10.76 (2.26) 4.54 a Overall problem sleeper 47.30 6.61 131 67.9 (61 75) 49.18 (6.44) 43.32 (5.03) 6.30 b a p<0.001; b p<0.001 by independent t-test. Freq., frequency; PS, problem sleeper, NPS, non-problem sleeper, CI, confidence interval. Table V: Parenting Stress Index-Short Form (PSI-SF) scores in problem and non-problem sleepers Problem sleepers Non-problem sleepers Mean 95% CI of t-score (n=62) (n=131) difference difference (df=191) Mean SD Mean SD Parental distress 36.41 7.62 32.18 7.45 4.23 1.93 6.54 3.63 a Parent child dysfunctional interaction 34.58 5.26 30.60 5.67 3.98 2.34 5.62 4.79 a Difficult child 37.69 7.22 32.08 6.19 5.61 3.51 7.71 5.27 a PSI-SF total score 108.68 15.29 94.85 16.01 13.82 9.10 18.55 5.77 a a p<0.001. df, degrees of freedom, CI, confidence interval. Sleep Problems of Children with Pervasive Developmental Disorders Sylvia Doo and Yun Kwok Wing 653

a sleep problem before the age of two was a significant risk factor (OR: 2.42, 95% CI 1.07 5.48) and borderline developmental delay was a protective factor (OR: 0.37, 95% CI 0.17 0.83). PARENTING STRESS AND SLEEP PROBLEMS The mean total PSI-SF score for the mothers was 104.69 while 82.6% of them scored above the cut-off point of 90 that indicated a significant level of stress. The mean total PSI-SF score for the fathers was 102.92 and 77.6% of them had a score above 90. There was no significant difference in the total PSI- SF scores between mothers and fathers. The problem sleeper group had higher scores than the nonproblem sleeper group on all three subscales (particularly for the difficult child subscale, t=5.27) and for total score (108.68 vs. 94.85, t=5.77; Table V). Furthermore, 89.3% (117/131) of problem sleepers and 64.5% (40/62) of nonproblem sleepers scored above the cut-off point. In the multivariate linear regression model, the total parenting stress score was positively associated with the total CSHQ score (β=0.352, t=5.237, p<0.001) and the presence of learning disability (β=0.196, t=2.919, p=0.004). In other words, a higher CSHQ score and a lower cognitive level of the children were associated with a higher level of parenting stress. The adjusted R 2 for the model was 0.141. Discussion We believe that this is the first study of sleep problems among Chinese children with PDD in Hong Kong. To the best of our knowledge, the current sample size is one of the largest among reported studies. The high response rate of 84% was the result of in-house consecutive recruitment. There was no formal registry or epidemiological study for children with PDD in Hong Kong. The high coverage rate of six government-run child assessment centres (seven in total, one being run by a university hospital) in the field of developmental paediatrics, together with the high response rate and the tight age range, supported the validity and how generalized these findings were for children with PDD in Hong Kong. The overall prevalence of problem sleepers as reported by the parents was high (67.9%). This is very close to the findings of other studies on Japanese and white children (Taira et al. 1988; Wiggs and Stores 1996, 2004; Patzold et al. 1998; Hering et al. 1999; Honomichl et al. 2002; Couturier et al. 2005; Polimeni et al. 2005). Although we did not include a comparison group, previous studies suggested a much lower rate (25%) of sleep problems among children without disabilities, even taking into account variation in age, ethnicity, cultural background, or socioeconomic status (Owens 2004). As in other studies, age-related changes in sleep patterns were noted (Taira et al. 1988, Richdale and Prior 1995, Honomichl et al. 2002). Despite the small age range of this sample, those younger than the age of 4 years were reported to have longer night waking times, longer naptimes, and a longer total sleep duration. Problem sleepers tended to sleep later and for a shorter time at night than their non-problem counterparts. In some children, their sleep patterns showed a marked variation. For example, bedtime during weekends ranged from 19:15 to 03:00 and the total sleep time ranged from 6 to 14.5 hours. The presence of sleep problems before the age of 2 was the most consistent factor related to an increased risk in subsequent sleep problems (five of the eight sleep problem subscales sleep onset delay, sleep duration, parasomnias, daytime sleepiness, and night waking and for general sleep problems). This is consistent with other studies which found that sleep problems in children with autism and other disabilities are chronic, have an early onset, and persist as the child grows (Quine 1991, Wiggs and Stores 1996, Richdale et al. 2000). If early identification and treatment can be implemented, the negative consequences of sleep problems, such as behavioural problems, may be reduced. The practice of having a regular bedtime was associated with a more than 50% reduction in bedtime resistance. This finding was consistent with the fact that maintaining a sleep routine is a well-known practice for promoting good sleep health at all ages (Mindell and Owens 2003). Sharing a room with parents or grandparents was associated with a lower risk of sleep anxiety. The implications of cosleeping for children s emotional and physical health remain controversial and show marked cultural differences (Latz et al. 1999, Owens 2004). Details of sleeping arrangements, particularly whether or not the child slept in the same bed as the parents, were not asked in this study. The effects of co-sleeping on children with PDD across different cultures need further investigation. On the other hand, sleep anxiety was positively correlated with males and with non-working mothers. Though it is well known that there is a high correlation between females and various types of anxiety disorders, the relationship between sex and sleep anxieties (particularly night time fears in this questionnaire) is still unclear. With regard to the economic status of the mothers, their mental status or stress levels may have played a mediating role on the children s emotion and behaviour. Housewives may have focused more attention on their children. Alternative postulation is that the children may have learned to deal with changes if their mother works. The association between the children s cognitive level and sleep problems appeared tenuous. After adjusting for age in the multivariate analysis, borderline developmental delay but not normal intelligence was related to a lower risk of sleep problems. However, the difference in overall cognitive level was only marginal (p=0.049). Thus, there may not be any actual differences in sleep problems across different intellectual functions in children with PDD (Patzold et al. 1998, Williams et al. 2004). Stress levels in parents with children with PDD have been found to be higher than in parents whose children have no developmental delay (Johnson 1996). Parents of children with PDD are particularly concerned about the future of their children including their cognitive impairment and ability to function independently, and the community acceptance of their children (Koegel et al. 1992). Local studies on the parental stress of children with PDD have reported a similar high prevalence rate and clinical profile (Fung 2002). Our study demonstrated that the presence of sleep problems was an independent factor leading to increased parental stress and was consistent with previous studies in that parents reported more frequent daily stresses (Schreck and Mulick 2000). Similarly, some studies have suggested that the presence of sleep problems significantly increases behavioural problems in children with general intellectual disabilities and increases hassle frequency and intensity in their parents (Richdale et al. 2000; Quine 1991, 2001). The relationships between child sleep and behavioural problems, and the stress experienced by parents are complex. Parental stress may be a cause 654 Developmental Medicine & Child Neurology 2006, 48: 650 655

or an effect of a child s sleep disturbance. It may be that having a child who sleeps badly, waking up frequently during the night, may have serious effects on parental stress levels via chronic sleep interruption. It may also be that stressed parents inadvertently contribute to or reinforce the sleep problems, perhaps by changes in the quality of their care and by indulging their children more (Quine 1991). Furthermore, stress levels can be modified by how the parents perceive and cope with the problem, particularly for children with developmental difficulties. Further study is suggested. This study has some limitations. The results were based on a cross-sectional report by the parents. More objective measures, such as a sleep log or an actigraph, were not used (Wiggs and Stores 2004). The actual sleep pattern of this group of children and causal inferences of significant factors could not be clearly drawn from the results. Conclusion In concordance with the studies of white and Japanese children, our study found that sleep problems are equally common in Chinese children with PDD and suggested that the sleep problems are related to the presence of PDD rather than to cultural practices. Moreover, sleep problems are an added stressor for their already highly stressed families. DOI: 10.1017/S001216220600137X Accepted for publication 30th January 2006. Acknowledgements We are grateful to Dr Catherine Lam and all the staff of the Child Assessment Service of the Department of Health, Hong Kong Special Administrative Region, for their enthusiasm and help in enrolling cases and collecting data. Special thanks go to all parents that participated in this study. Without their support, the study would never have materialized. We would also like to thank Dr Judith Owens for allowing us to use the CSHQ. References American Psychiatric Association. (1994) Diagnostic and Statistical Manual of Mental Disorders. 4th edn. 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