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 RESEARCH ARTICLE

Impact of family environment on the development of tic disorders: Epidemiologic evidence for an association

Soon-Beom Hong, MD, PhD

Division of Child and Adolescent Psychiatry, Department of Psychiatry, Seoul National University College of Medicine, Seoul, Republic of Korea

Jae-Won Kim, MD, PhD

Division of Child and Adolescent Psychiatry, Department of Psychiatry, Seoul National University College of Medicine, Seoul, Republic of Korea

Min-Sup Shin, PhD

Division of Child and Adolescent Psychiatry, Department of Psychiatry, Seoul National University College of Medicine, Seoul, Republic of Korea

Yun-Chul Hong, MD, PhD

Department of Preventive Medicine, Seoul National University College of Medicine and Institute of Environmental Medicine, Seoul, Republic of Korea

Eun-Jin Park, MD

Department of Psychiatry, Ilsan Paik Hospital, Inje University College of Medicine, Goyang, Republic of Korea

Boong-Nyun Kim, MD, PhD

Division of Child and Adolescent Psychiatry, Department of Psychiatry, Seoul National University College of Medicine, Seoul, Republic of Korea

Hee-Jeong Yoo, MD, PhD

Division of Child and Adolescent Psychiatry, Department of Psychiatry, Seoul National University College of Medicine, Seoul, Republic of Korea

In-Hee Cho, MD, PhD

Department of Psychiatry, Gil Medical Center, Gachon University of Medicine and Science, Incheon, Republic of Korea

Soo-Young Bhang, MD, MPH

Department of Psychiatry, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan, Republic of Korea

Soo-Churl Cho, MD, PhD

Division of Child and Adolescent Psychiatry, Department of Psychiatry, Seoul National University College of Medicine, Seoul, Republic of Korea

BACKGROUND: Although family education generally is recommended in the treatment of tic disorders, few studies have focused on the relationship between family environment and diagnosis of tic disorders.

METHODS: Presence of DSM-IV tic disorders was determined in a general population of 921 children in Korea from 2008 to 2009. Clinical risk factors were assessed, including comorbidity with attention-deficit/hyperactivity disorder; family-related factors such as the number of family members and primary caretaker of the child; and socioeconomic factors in the form of paternal education level and household yearly income. Multivariable logistic regression analyses were performed to estimate the association between a list of clinical, familial, and social variables and the odds of developing tic disorders.

RESULTS: At Bonferroni corrected thresholds, a higher risk of tic disorders was significantly associated with the number of changes in primary caretaker, whereas a lower risk was associated with increasing number of children in the family.

CONCLUSIONS: Family-related environmental factors may play a role in the development or exacerbation of tic disorders. The results advocate the importance of family education when treating children with tic disorders, and further research is needed on the contextual risk factors of tic disorders.

KEYWORDS: tic disorders, Tourette’s syndrome, family environment, primary caretaker

ANNALS OF CLINICAL PSYCHIATRY 2013;25(1):50-58

  INTRODUCTION

Tic disorders are common neurobehavioral conditions of childhood characterized by transient or chronic manifestation of a single or multiple movements and/or vocalizations called tics.1 The etiology of tic disorders is thought to involve genetic and environmental factors. For the former, a large body of evidence supports a strong genetic contribution2,3 and there has been a long-standing consensus for the primary genetic basis for tic disorders.4 However, specific inheritance pattern of tic disorders still remains unknown, and no replicated genetic risk factors have been found, despite research efforts including a series of genome-wide, multi-center association studies.5-7

Regarding the nongenetic factors, both the biologic environmental and psychosocial contextual factors were suggested.8 As for the latter, symptom exacerbations in tic disorders seem to follow antecedent life stress.9,10 In clinical practice, a wide consensus prevails regarding that tic disorders are “stress-sensitive,” and accordingly, treatment recommendations generally include educating patients and their caretakers about the impact of psychosocial stress on tic symptoms.11,12 However, despite family education being widely recommended in clinical settings, few studies have focused on the relationship between family environment and diagnosis of tic disorders. We hypothesized that if many clinicians agree on the potential benefit of this education strategy for tic disorders, family structure and parenting status might play an important role in the etiology or severity of these disorders.

A community-based exploratory investigation on the relationship between familial factors and diagnosis of tic disorders in Korean school-aged children was conducted. In consideration of the type of tic disorders, we noted that most studies have focused on Tourette’s syndrome, but according to Roessner et al13 “we have almost no data on phenomenology, prognostic factors, etiology, and pathophysiology of transient tic disorders.” Therefore, in this study we investigated children with tic disorders comprising Tourette’s syndrome, chronic motor or vocal tic disorder, and transient tic disorder.

  METHODS

Participants were recruited from 5 administrative regions in Korea, among which Seoul and Seongnam are urban cities, Incheon and Ulsan are industrial cities, and Yeoncheon is a rural district. We selected 2 or 3 schools from each city that well represented local demographics, and sent invitation letters to parents of children in third or fourth grade (age range 8 to 11) to participate in our study. Detailed information about the study was given to parents and children, and then written informed consent was obtained before study entry. The study protocol was approved by the institutional review board of the Seoul National University Hospital.

Diagnosis of the child’s tic disorders

We assessed the presence of tic disorders or attention-deficit/hyperactivity disorder (ADHD) in children using a highly structured diagnostic interview, the Diagnostic Interview Schedule for Children Version IV (DISC-IV).14 For this study, we only used the tic disorders and ADHD diagnostic modules. Good test-retest reliability has been reported for the original version of the DISC-IV, and the Korean version also has shown good reliability and validity.15

Assessment of the child’s intelligence

Each child was also administered the abbreviated form of the Korean Educational Development Institute’s Wechsler Intelligence Scales for Children (KEDI-WISC).16 Scores from the abbreviated battery are known to highly correlate with the WISC full scale intelligence quotient (IQ), both in the translated original instrument, WISC-R,17 and in the age-standardized Korean version, KEDI-WISC.18

Assessment of possible environmental risk factors

Parents also completed a questionnaire about demographic and other relevant data, including the primary caretaker of the child, number of changes in primary caretaker, number of family members, paternal education level, and yearly income of the family.

Statistical analyses

We first assessed the differences between children with tic disorders and without tic disorders by using Student t tests for continuous variables and chi-square tests, Fisher exact tests, or linear-by-linear association tests for categorical variables. We performed multivariable logistic regression analyses to estimate the association between a list of demographic, clinical, and familial variables and the odds of developing tic disorders. We repeated the same analyses with only male participants, taking into account the male predominance of tic disorders. Because some family-related variables such as primary caretaker of the child and number of family members can be considered to reflect socioeconomic status, we have added exploratory analyses by splitting our sample into high and low income groups and running the logistic regression separately. Lastly, there is a chance to consider transient tic disorder as a separate entity from Tourette’s syndrome or chronic motor or vocal tic disorder, with the former being a normative developmental phenomenon and the latter 2 being chronic disease conditions. Therefore, we have further analyzed separately, by mutually excluding between the former and the latter 2 in the outcome definition. All reported probabilities were 2-tailed, and an alpha level of 0.05 was considered statistically significant. All analyses were performed with SPSS 19.0 (SPSS Inc., Chicago, IL, USA).

  RESULTS

Among 921 participants, we identified 21 (2.2%) patients with a tic disorder (1 with Tourette’s syndrome, 12 with chronic motor or vocal tic disorder, and 8 with transient tic disorder; TABLE 1). In the multivariable logistic regression analyses, number of changes in primary caretaker was significantly associated with a higher risk of having a tic disorder, while increasing number of children in the family was significantly associated with a lower risk (TABLE 2). Only these 2 variables survived the Bonferroni correction, and the results from the male participants did not substantially change (TABLE 3).


TABLE 1

Demographic characteristics of subjects

Characteristics N=921 Tic (+) N=21 Tic (-) N=900 P
Age (years, mean±SD) 9.05±0.70 9.39±0.49 9.04±0.70 .02
Sex (female, %) 47.0 4.8 48.0 .00
Paternal education (years, mean±SD) 13.80±2.17 13.80±2.04 13.80±2.18 .99
Yearly income >$25,000 (%) 62.7 57.9 62.9 .65
Number of family members        
  Adults (mean±SD) 2.13±0.61 2.10±0.31 2.13±0.62 .81
  Children (mean±SD) 1.81±0.86 1.55±1.09 1.82±0.86 .19
Number of changes in primary caretaker (mean±SD) 0.20±0.62 0.52±1.12 0.19±0.60 .19
Primary caretaker of the child       .76
  Mother (%) 84.7 81.3 84.9  
  Father (%) 0.8 6.3 0.6  
  Grandparent (%) 12.3 6.3 12.4  
  Others (%) 2.2 6.3 2.1  
Child’s IQ (mean±SD) 110.75±14.18 115.67±14.81 110.63±14.15 .10
Presence of ADHD (%)   14.3 5.0 .09
Student t tests and chi-square tests (Fisher exact tests or linear-by-linear association tests, as appropriate) were used for continuous and categorical variables, respectively.
ADHD: attention-deficit/hyperactivity disorder; IQ: intelligence quotient; SD: standard deviation.

TABLE 2

The relationship between clinical, familial, and social risk factors and the diagnosis of tic disorders (N=921)

  Model 1 Model 2 Model 3 Model 4
OR P 95% CI OR P 95% CI OR P 95% CI OR P 95% CI
Number of adults in the family 1.05 .892 0.47 to 2.34 1.00 .994 0.42 to 2.35 0.97 .953 0.39 to 2.37 0.95 .918 0.36 to 2.48
Number of children in the family 0.42 .011 0.21 to 0.82 0.44 .020 0.22 to 0.87 0.33 .005 0.15 to 0.72 0.32 .005 0.14 to 0.71
Changes in primary caretaker 2.23 .001 1.38 to 3.61 2.10 .005 1.25 to 3.53 2.29 .002 1.34 to 3.91 2.23 .004 1.29 to 3.83
Primary caretaker of the child                        
  Mother (reference)                        
  Father 15.81 .020 1.55 to 160.92 12.40 .042 1.09 to 140.84 15.97 .031 1.29 to 197.25 49.11 .010 2.51 to 957.95
  Grandparent 0.39 .380 0.04 to 3.18 0.54 .578 0.06 to 4.54 0.48 .504 0.05 to 4.12 0.46 .490 0.05 to 4.16
  Others 2.54 .418 0.26 to 24.40 2.12 .537 0.19 to 23.45 2.21 .531 0.18 to 26.65 1.88 .622 0.15 to 23.21
Age (years)       1.94 .123 0.83 to 4.53 1.60 .291 0.66 to 3.87 1.84 .191 0.73 to 4.64
Sex                        
  Male (reference)                        
  Female       0.10 .034 0.01 to 0.84 0.11 .037 0.01 to 0.87 0.12 .049 0.01 to 0.99
Paternal education (years)             1.05 .748 0.78 to 1.41 1.00 .966 0.73 to 1.37
Yearly income                        
  >$25,000 (reference)                        
  <$25,000             1.16 .810 0.33 to 4.13 1.48 .554 0.39 to 5.55
Child’s IQ                   1.05 .053 0.99 to 1.12
ADHD                        
  No (reference)                        
  Yes                   0.66 .756 0.04 to 9.06
  χ2 df P χ2 df P χ2 df P χ2 df P
Likelihood ratio 18.52 6 .0050 30.28 8 .0001 32.55 10 .0003 37.02 12 .0002
We checked the variance inflation factor (VIF) for all the independent variables and found that no VIF was >1.13 throughout the models.
Bold numbers indicate significance after Bonferroni correction for the number of predictors in the models.
ADHD: attention-deficit/hyperactivity disorder; df: degree of freedom; IQ: intelligence quotient; OR: odds ratio.

TABLE 3

The relationship between clinical, familial, and social risk factors and the diagnosis of tic disorders in male children (N=488)

  Model 1 Model 2 Model 3 Model 4
OR P 95% CI OR P 95% CI OR P 95% CI OR P 95% CI
Number of adults in the family 0.92 .861 0.37 to 2.26 0.84 .718 0.32 to 2.17 0.82 .713 0.30 to 2.24 0.79 .662 0.27 to 2.26
Number of children in the family 0.43 .020 0.21 to 0.87 0.45 .030 0.22 to 0.92 0.32 .007 0.14 to 0.73 0.31 .007 0.13 to 0.73
Changes in primary caretaker 2.18 .003 1.31 to 3.62 2.15 .005 1.26 to 3.69 2.37 .003 1.35 to 4.17 2.31 .004 1.31 to 4.10
Primary caretaker of the child                        
  Mother (reference)                        
  Father 13.45 .034 1.20 to 149.61 13.14 .039 1.14 to 151.41 15.65 .034 1.23 to 198.07 37.23 .016 1.97 to 702.84
  Grandparent 0.50 .527 0.06 to 4.18 0.63 .672 0.07 to 5.33 0.55 .600 0.06 to 4.93 0.55 .599 0.05 to 5.12
  Others 1.86 .611 0.16 to 20.58 2.12 .547 0.18 to 24.67 2.25 .534 0.17 to 29.24 1.91 .626 0.14 to 26.11
Age (years)       2.10 .103 0.86 to 5.15 1.72 .251 0.68 to 4.34 1.89 .193 0.72 to 4.98
Paternal education (years)             1.01 .935 0.74 to 1.37 0.97 .897 0.71 to 1.34
Yearly income                        
  >$25,000 (reference)                        
  <$25,000             1.30 .702 0.33 to 5.01 1.54 .540 0.38 to 6.22
Child’s IQ                   1.04 .169 0.98 to 1.10
ADHD                        
  No (reference)                        
  Yes                   0.60 .706 0.04 to 8.18
  χ2 df P χ2 df P χ2 df P χ2 df P
Likelihood ratio 15.71 6 .0153 18.57 7 .0096 22.04 9 .0087 24.45 11 .0109
We checked the variance inflation factor (VIF) for all the independent variables and found that no VIF was >1.14 throughout the models.
Bold numbers indicate significance after Bonferroni correction for the number of predictors in the models.
ADHD: attention-deficit/hyperactivity disorder; df: degree of freedom; IQ: intelligence quotient; OR: odds ratio.

In the following exploratory analyses, for reasons of small sample sizes, we used only these 2 explanatory variables shown to be significantly associated with the odds of having a tic disorder according to the main analyses, and adjusted for the other hypothesized variable of interest—primary caretaker of the child—as the only covariate. When the multivariable logistic regression was performed separately according to the dichotomized income status, in the higher income families, number of changes in primary caretaker and number of children in the family both remained significantly associated with the odds of having a tic disorder. However, in the lower income families, only number of changes in primary caretaker was significantly associated with the risk of having a tic disorder (TABLE 4). Further, when presence of Tourette’s syndrome or chronic motor or vocal tic disorder and not transient tic disorder was defined as the outcome, the number of changes in primary caretaker and number of children in the family again remained significantly associated with the odds of having a tic disorder (TABLE 5). However, when presence of transient tic disorder only was defined as the outcome, number of children in the family was no longer significantly associated with the risk of having a tic disorder.


TABLE 4

The relationship between familial risk factors and the diagnosis of tic disorders according to socioeconomic status

  Model 1 (N = 549): yearly income >$25,000 Model 2 (N = 326): yearly income <$25,000
B SE OR P 95% CI B SE OR P 95% CI
Number of children in the family -1.16 0.46 0.31 .013 0.12 to 0.77 -0.97 0.67 0.37 .152 0.10 to 1.43
Changes in primary caretaker 0.84 0.29 2.31 .005 1.29 to 4.13 1.23 0.51 3.42 .016 1.25 to 9.35
  χ2 df P χ2 df P
Likelihood ratio 13.01 5 .0232 13.41 5 .0197
Both models were adjusted for primary caretaker of the child.
B: unstandardized regression coefficient; df: degree of freedom; OR: odds ratio; SE: standard error.

TABLE 5

The relationship between familial risk factors and the diagnosis of tic disorders according to disease spectrum (N = 921)

  Model 1: Tourette’s syndrome or chronic tic disorders Model 2: Transient tic disorders
B SE OR P 95% CI B SE OR P 95% CI
Number of children in the family -1.34 0.49 0.26 .007 0.09 to 0.69 -0.33 0.49 0.71 .500 0.27 to 1.89
Changes in primary caretaker 0.83 0.30 2.30 .007 1.25 to 4.20 0.66 0.31 1.94 .035 1.04 to 3.59
  χ2 df P χ2 df P
Likelihood ratio 17.04 5 .0044 7.27 5 .2012
Both models were adjusted for primary caretaker of the child.
B: unstandardized regression coefficient; df: degree of freedom; OR: odds ratio; SE: standard error.

  DISCUSSION

The study has examined the relationship between possible environmental risk factors and the diagnosis of a tic disorder in a community sample of school-age children. The results suggest that frequent changes in primary caretaker and perhaps possibly the father being the primary caretaker of the child might be risk factors for tic disorders. Also, the results suggest that siblings might be a protective factor against tic disorders.

Among the hypothesized environmental factors for developing a tic disorder, psychologically-oriented contextual risk factors of tic disorders also have been suggested. In this regard, there was an interesting case report of a 9-year-old boy whose tic frequencies worsened in the presence of his father, who took a punitive stance against the tic symptoms.19 More recently, studies have suggested that environment-specific variables—such as being at home or in the clinic, or attending class—might influence tic severity.20,21 Researchers have reported that a conversation about or overt observation of the child’s tic symptoms also might influence tics.20,22 These previous reports were a rationale for our studying the influence of family-related environmental factors on tics.

In addition, many studies have suggested that emotional factors influence tic expression as well. Emotional variables including anxiety, frustration, stress, or tension seem to aggravate tics.10,23-27 Putting these variables and our results together, an unstable family environment reflected as frequent changes in primary caretaker, and perhaps a consequent development of insecure attachment, might contribute to tic symptoms. Another possible argument in relation to our results is whether fathers tend to talk or act in a way that is more stress-inducing or tic-provoking to the child than mothers or grandparents do, at least to a child with increased vulnerability for developing tic disorders. This is worth further investigation because educating family members of children with tic disorders is recommended as an important treatment strategy. The present study perhaps suggests the clinical importance of educating fathers.

Recently, Lawson and Mace28 have demonstrated that, contrary to common belief, a large sibship size did not have a negative impact on mental health, and they argued that everyday interaction with siblings might provide some socializing benefit, which offsets the possible negative impact of decreased parental time with each child. Gass et al29 also have shown that self-reported affectionate relationships with siblings might promote a child’s adjustment to stressful life events. Bras et al,30 on the basis of a large nationwide registry database, have presented similar discussions. These are consistent with our finding that number of siblings was negatively associated with the odds of having tic disorders. Another study showing that higher maternal parity was associated with increased risk of psychiatric morbidity in the offspring also showed that having no more than 2 or 3 siblings had beneficial effects compared with having no sibling.31 This is consistent with a mean of 1.81±0.86 children in the family in our sample.

The idea that a large sibship size can have negative impacts was based on the possibility that parental resources would be divided accordingly.28 With this regard, we have split our sample into higher and lower income status groups, assuming this as a proxy of parental resources, and rerun the main analyses (TABLE 4). The results showed that the protective effect of a large sibship size against tic disorders might not be evident in the lower socioeconomic status group. In other words, lack of household resources might offset the beneficial effect of a large sibship size. This exploratory split analysis is supported by the recent report that mental health and level of income are closely related.32 However, the loss of statistical significance might be due to the decreased sample sizes in the split groups (n=549 and 326 in the higher and lower income groups, respectively). In fact, 46 participants (4.9%) refused to provide information about their income or left the item blank on the questionnaire sheet. Although a considerable amount of data are missing regarding the income status, we provide these results to supplement Mathews et al,33 which was based on Hollingshead scores obtained from approximately one-third of the total sample. More recently, another study showed that being an only child was a social environmental risk factor for psychiatric disorders.34 This study also showed that behavior restriction by the father was a risk factor.

We performed another set of supplemental analyses. As a result, when presence of Tourette’s syndrome or chronic motor or vocal tic disorder was defined as the outcome, number of changes in primary caretaker and number of children in the family were both significantly associated with the odds of having a tic disorder. However, when presence of transient tic disorder only was defined as the outcome, the associations were either attenuated or lost (TABLE 5). This is perhaps in accord with results from classic twin studies showing that the concordance rate for Tourette’s syndrome was much lower compared with the rate estimated including other tic disorders.4,35 However, no data was available on the concordance rate of transient tic disorder only, and our preliminary results need to be replicated.

A further consideration for interpreting our results is that epidemiological studies of childhood tic disorders have shown variation between Western and non-Western countries, with slightly lower prevalence of Tourette’s syndrome in East Asian countries.36 Including other tic disorders, the reported prevalence estimates vary greatly.37 It is unknown how much of this variation reflects a true difference in prevalence in the context of methodological differences among studies (eg, study population, screening and confirmation protocols, assessment tools, or diagnostic criteria). However, sociocultural differences might provide additional explanations.

In Korea, as in other East Asian countries, many fathers are an authoritarian figure in the family and the traditional view that child rearing is a woman’s job continues to be a social influence. Many Korean mothers stay at home and women’s employment rate in Korea, especially after childbirth, is lower than in Western countries (eg, the highest gender employment gaps among Organization for Economic Co-operation and Development countries were observed in Turkey, Mexico, Greece, Korea, and Italy),38 probably resulting in less frequent changes in primary caretaker on average. In contrast, relatively higher rate of women’s employment and parental separation or divorce in Western countries may increase primary caretaker changes. Taken together, the prevalence variation of tic disorders among countries may be partly caused by culturally specific sex roles that influence changes in primary caretakers. In support of this idea, the lowest tic prevalence reported in Western population was from Italy,39 where changes in family structure (eg, characterized by having fewer children, more frequent divorce, increased extramarital birth rate, and higher odds of single parenthood) are below that of other European and North American countries.40

Cultural differences also may have contributed to the association between tic disorders and having a father as a primary caregiver. In Korean tradition, the father is often a patriarchal, authoritarian figure who would apply strict discipline and punitive parenting to a child with tic symptoms leading to exacerbation of symptoms. However, because authoritarian fathers who consider child rearing a woman’s job likely will not spend much time with their children, we assume that they do not contribute to the general increase of tic prevalence and they only matter when they become the primary caretaker of the child, which is not common in Korea. Also, we doubt that this phenomenon applies with the same intensity to fathers around the globe because different cultural backgrounds should play important roles. In Korea—and probably in other East Asian countries as well where many aspects of life are in the middle of rapid westernization—it would be interesting to follow up how reported prevalence of tic disorders changes in the next generation.

This study has some limitations. First, the study was of a cross-sectional observational design, and therefore the inference about causality was only based on our hypothesis. Second, although the original sample size was substantial and results were corrected stringently, the low prevalence of tic disorders in the general population resulted in a restricted final sample, and this limitation might have lead to the large confidence intervals in some of our results. This was especially the case when estimating the influence of the father being the primary caretaker of the child. Third, no instrument for evaluating tic severity or psychological stress of the child was administered in this study. Measurement of tic severity—eg, number, frequency, intensity, complexity, and interference of tic symptoms41—would have strengthened our results. And lastly, the majority of our results mixed different spectrum of tic disorders. Considering the small sample size of individuals with tic disorders and absence of tic severity measurements, future studies are warranted with recruitment of more affected individuals from an enriched sample and a wider range of evaluation relevant to tic disorders.

  CONCLUSIONS

These results suggest that family-related environmental factors might play a role in the development or exacerbation of tic disorders. Clinically, these results advocate for the ongoing importance of family education when treating children with tic disorders, and for future etiological research into both genetic and environmental factors together and both biologic and contextual environmental factors together.

DISCLOSURES: The authors report no financial relationship with any company whose products are mentioned in this article or with manufacturers of competing products. This work was supported by a grant (091-081-059) from the Korean Ministry of Environment (Eco-Technopia 21 Project). The funder had no role in the design and conduct of the study; the collection, analysis, and interpretation of the data; or the preparation, review, or approval of the manuscript.

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CORRESPONDENCE: Soo-Churl Cho, MD, PhD, Division of Child and Adolescent Psychiatry, Department of Psychiatry, Seoul National University College of Medicine, 101 Daehak-No, Chongno-Gu, Seoul, Republic of Korea, E-MAIL: soochurl@snu.ac.kr