Introduction
Children with Down syndrome (DS) are a large group of children with special needs [1, 2]. DS is one of the most common genetic abnormalities [3, 4], causing various degrees of mental retardation [5]. The incidence of DS in America is estimated at 6000 children annually [6]. The incidence of this disorder in the world is 1 in every 700-800 live births [7], although it has increased in recent years [8]. These children usually are exposed to chronic physical diseases, developmental problems, and behavioral and emotional problems [9], so they need additional care [10, 11]. 
The birth of a child with DS creates various problems for parents and may lead to mental confusion to the point of suicide in them [12]. Parents’ commitments and their daily responsibilities in life are affected, resulting in stress, anxiety, and depression [13]. In addition, the burden of caring for a disabled child can harm parents’ quality of life [14]. Some parents experience pessimism, anger, guilt, and despair. Finally, parents’ depression and feelings of hopelessness may reduce their ability to properly care for the children and cause negative consequences for the children [15]. The parents of children with DS often care for these children throughout their lives due to the extent and permanence of the symptoms of this disorder [16]. Therefore, they experience many tensions that can affect their health [17]. So far, various studies have been conducted to investigate the caregiver burden in parents of children with various physical, mental, and developmental disorders. El-Din et al. investigated the caregiver burden in the parents of children with DS in Egypt and reported that the parents of these children experience mild to severe caregiver burden [7]. Ilhan et al. also investigated the caregiver burden and depression in the family of children with DS in Turkey. Their results show that the mothers of these children bear a lot of caregiver burden and are exposed to much depression due to this burden [9]. In another study, It was found that the caregiver burden for parents of children with DS is higher than parents with normal children, but it is less compared to parents of children with autism [18]. Determining the caregiver burden in the parents of children with DS and related factors can provide therapists, researchers, and decision-makers with appropriate information regarding the conditions of the parents of the child. Since therapists and specialists of children with DS have the most interaction and communication with them and their parents, their awareness of the factors related to caregiver burden can help in the process of treatment and rehabilitation of these children. Therefore, therapists must evaluate factors related to the caregiver burden on parents. Considering a few studies in the field of caregiver burden in Iran and the necessity of examining the caregiver burden in the parents of these children, it seems necessary to conduct studies in this field. Therefore, the present study was conducted to investigate the caregiver burden in parents of children with DS. 
Materials and Methods
The present study was descriptive/analytical cross-sectional. We used a convenience sampling method to select the study samples from the parents of children with DS who visited rehabilitation clinics in Tehran City, Iran, and were willing to participate. The inclusion criteria included parenting the children with DS according to the medical record, the age range of 4-12 years for the child, the direct responsibility of taking care of the child, and parents’ clean records from any physical or mental disorders. Also, parents who did not want to continue the study had another child with any mental or physical disorders or did not sign the consent form were excluded from the study. 
The study data were collected using a demographic information questionnaire and Novak’s caregiver burden questionnaire [19]. The participants in the study completed these two questionnaires. The caregiver burden questionnaire has 24 items, created by Novak and Guest in 1989 to measure the caregiver burden [19]. This questionnaire has five subscales, such as time-dependent caregiver burden with 5 items (1-5), evolutionary caregiver burden with 5 items (6-10), physical caregiver burden with 4 items (11-14), and social caregiver burden with 5 items (15 to 19), and emotional caregiver burden with 5 items (20-24). Caregivers’ answers are measured on a 5-point Likert scale (completely false to completely true). Based on this, the scores of this questionnaire range from 24 to 120. According to the average scores of the total caregiver burden, scores of 24 to 39 were considered mild caregiver burden, 40 to 71 moderate caregiver burden, and 72 to 120 severe caregiver burden. This questionnaire has good reliability, and the Cronbach alpha coefficient for the subscales has been reported from 0.69 to 0.87, and the Cronbach alpha coefficient for the whole questionnaire is 80 [19, 20]. This tool has been validated by Abbasi et al. (2011) in Iran. In a preliminary study by Abbasi et al. with a sample of 40 caregivers of hemodialysis patients, the Cronbach alpha coefficient of the scale was 90, and the alpha coefficient of its subscales was 82-76 [21]. Also, in Salmani et al.’s research, the content validity of this questionnaire was confirmed, and the reliability of this tool was 92 using the Cronbach alpha method [22]. 
Data were analyzed with SPSS software v.21. Mean, standard deviation, and minimum and maximum values ​​were used to describe the data. The investigation of normal distribution was done using the Kolmogorov-Smirnov test. To check the correlation between caregiver burden scores and the variables of parents’ age, child’s age, number of children, and parents’ income, because the data does not have a normal distribution (P<0.05), the Spearman non-parametric test was used. The Mann-Whitney U test was used to examine parental caregiver burden in 2-state variables, such as parents’ gender, parents’ marital status, children’s gender, and the status of receiving special education because the data does not have a normal distribution. Also, the Kruskal-Wallis test was used in multi-state variables, such as education, parents’ occupation, and children’s status and special needs. The significance level was considered less than 0.05 for all statistical analyses. 
Results
In this study, 150 parents of children with DS participated. A total of 59 people (39.33%) were men, and 91 people (60.67%) were women. The Mean±SD age of the participants in the research was 38.78±7.92 years, and the minimum and maximum age of the participants was 22 and 60 years, respectively. Regarding marital status, 92% of the parents were married, and 8% had separated from their spouses, or their spouses had died. A total of 2.7% of the parents participating in the research were illiterate, 4.7% had primary education, 20.7% had a high school education, 33.2% had a diploma, and 13.3% had an associate degree, 20.7% had a bachelor’s degree, and 4.7% had a master’s degree and higher education. Regarding employment status, 20% of the parents participating in the research were employees, 50% were self-employed, 1.3% were unemployed, and 28.7% were homemakers. By examining the variable of income status, the results showed that 37.3% of the parents participating in the research had an income of less than 3 tomans, 38% an income between 3 and 5 tomans, 14.7% between 5 and 7 tomans, and 10% have an income of 7 million and more. Regarding the number of children, 37.3% of the participants in the research have one child, 44% 2 children, and 18.7% 3 or more children. By examining the gender variable of children with DS, 60% were boys, and 40% were girls, the mean±SD age of children with DS was 7.14±2.38 years, and the minimum and maximum age of the subjects was 4 and 12 years. Regarding the caregiver status variable, the results showed that 7.3% of children do not receive special care and 20% receive daily care, 24% at night, and 48.7% receive round-the-clock care.
The study results showed that the mean±SD scores of the total caregiver burden of parents and its subscales were as follows: total caregiver burden, 68.12±17.51; time caregiver burden, 15.95±5.2; evolutionary caregiver burden, 15.46±4.84; mental caregiver burden, 12.226±4.853; physical caregiver burden, 11.24±4.47; and social caregiver burden, 11.18±4.94. These results showed that, on average, parents of children with DS bear an average caregiver burden. Also, 14.2% of parents experienced mild caregiver burden, 62.6% moderate caregiver burden, and 23.2% severe caregiver burden (Table 1).


The results of examining the relationship between the variables of parents’ age and income, number of children, and child’s age using the Spearman correlation test showed a significant and direct relationship between the number of children and the total parental caregiver burden score, as well as a significant and inverse relationship between their age and income and the child’s age (P<0.05) (Table 2).


While the Mann-Whitney U and Kruskal-Wallis tests showed that factors such as parents’ gender, child’s gender, parents’ marital status, parents’ education, receiving special education, care needs, and care status do not affect the amount of parental caregiver burden. (P>0.05). For example, the average score of the total caregiver burden of mothers and fathers was 70.63 and 65.62, respectively. Also, no statistically significant difference was observed between mothers and fathers in the average caregiver burden score in the subscales (P>0.05). The results showed that the average score of subscales of time caregiver burden, emotional caregiver burden, evolutionary caregiver burden, physical caregiver burden, and social caregiver burden for mothers were 16.48, 12.98, 16.01, 11.88, and 11.65 and for fathers, 15.21, 11.43, 15.1, 10.74, and 10.61, respectively. The average score of the total caregiver burden of parents of boys and girls was 68.86 and 67.36, respectively. Table 3 presents the details related to comparing the caregiver burden of parents and the mentioned variables.


Discussion
The present study showed that parents of children with DS experience an average caregiver burden. Factors such as parents' age, child's age, parents' income, and the number of children in the family influence the caregiver burden, and factors such as marital status, parents' occupation, and the child's gender are not determining variables in caregiver burden. The present study showed that parents with a younger age have significantly more caregiver burden. These results were consistent with the results of Caqueo [23], Lee et al. [24], and Abbasi et al. [25]. Older parents probably have more tolerance and better ability in stressful situations. The younger the parents' age, the more likely they will not be able to adapt to the problem for their child, and on the other hand, usually at younger ages, more economic problems exist that affect the caregiver burden. Zahid's study [26] in Kuwait and Agren et al. [27] in America did not report a significant relationship between age and caregiver burden. The reason for the difference in the results of the studies can be related to the difference in the culture and welfare level of the countries. 
In this study, the gender of the parents of children with DS had no effect on the caregiver burden. The results of studies in this field are conflicting. Mangdan et al. reported that the gender of parents of children with mental disorders does not affect their caregiver burden [28]. In Al Din et al.'s study [7], mothers of children with DS have more caregiver burden. Fitzgerald et al. [29] reported that mothers of children with cystic fibrosis bear more caregiver burden. In Ilhan et al.'s study [9], only children's mothers participated, and it was impossible to compare the results based on the parent's gender.
In the present study, parents' education level did not cause a significant difference in caregiver burden. Zahid et al. [26] and Lee et al. [24], in their research, pointed out a significant relationship between caregiver burden and education level. The results of Adeosum's study show that people with low education have more caregiver burden. Probably, parents with a higher level of education have a better performance in identifying the problems of children with DS and adapting to them than parents with a lower level of education. 
Parents with higher incomes had less caregiver burden. Similar studies have also shown an inverse and significant relationship between financial status and caregiver burden. Meshaikhi et al. [30], Garlo et al. [31], and Lee et al. [24] also reported an inverse relationship between income and caregiver burden. A poor economic situation is associated with a greater caregiver burden which can be due to the loss of parents' jobs or the additional costs of children's treatment that are imposed on parents. Salmani et al. [22] also reported results consistent with this study.
The present study's findings showed a significant direct relationship between the number of children and the caregiver burden of parents. With the increase in the number of children, the social and especially economic needs of the parents caring for disabled children increase; as a result, it imposes a heavy caregiver burden on the parents of these children. Other results of the research showed a significant inverse relationship between the age of the child and the parents' caregiver burden. It can be said that as the age of the disabled child increases, the parents' caregiver burden decreases and vice versa. Because DS is a lifelong problem, the family is forever faced with its negative consequences, which has a special effect on providing services to these children. At birth, infancy, childhood, and adulthood, a disabled child imposes special costs on the family economy. 
Examining the impact of receiving special education for parents showed that this factor variable is not significant, although parents with a higher level of literacy and awareness about this disease and their children's needs receive less burden of care and vice versa. This result is consistent with the research findings of Sola et al. [32]. They reported that mothers with a higher level of awareness about taking care of their children experienced less caregiver burden in caring for them and coping with their needs. The higher the level of education and awareness of the parents of disabled children, the more they feel the need to take care of their child to adapt to the existing environment in the best way. As a result, they try to get more information to reduce the care and extra burden. By participating in workshops and special education classes, they try to get familiar with their child's needs and care for him; as a result, they can better deal with the child's problems.
The current study showed that the caregiver needs of children could affect the caregiver burden of parents, and the higher the caregiver needs of children, the more parents bear more caregiver burden. Children who have a lower level of intelligence are usually unable to estimate their basic needs, and in this situation, they must spend most of their time meeting these needs [33]. 
This study showed that the number of caregiving hours could affect the caregiver burden of parents. The more hours of child care, the more parents experience caregiver burden. The obtained results are consistent with the findings of Dalvandi et al. [34]. Therefore, for children who need round-the-clock care, parents usually spend most of their time taking care of these children, and the leisure and entertainment plans of parents are disrupted because parents stay home to take care of their children, and sometimes they suffer more mental and physical problems [35]. 
The limitations of the present study include the use of convenience sampling and including the participating parents from Tehran City. The severity of children's disorders in this study was not determined in terms of different motor, cognitive, and communication skills. It is suggested that future studies compare the caregiver burden of parents of children with DS with parents of children with other disorders, such as autism, cerebral palsy, and other developmental disorders.
Conclusion 
The present study showed that the parents of children with DS experience an average caregiver burden, and the highest caregiver burden included temporal caregiver burden, evolutionary caregiver burden, mental caregiver burden, physical caregiver burden, and social caregiver burden. According to the role of parents in the process of health, care, and rehabilitation of children, it is better for therapists, specialists, and health decision-makers to pay special attention to the conditions and status of parents of children with DS and the impact of the child's problem on them. 

Ethical Considerations
Compliance with ethical guidelines
All ethical principles were observed in this study. All participants voluntarily participated in the study and completed a written consent form. All participants were informed about the process of conducting the research and were also allowed to withdraw from the research at any time. All information about the people was examined confidentially. The present study was approved by the Ethics Committee of Semnan University of Medical Sciences (code: IR.SEMUMS.REC.1395.162).

Funding
This article is the result of the research project approved by Semnan University of Medical Sciences Student Research Committee No. 1146 and was conducted with the financial support of Semnan University of Medical Sciences. 

Authors' contributions
Conceptualization, editing and finalization: Hossein AliBakshi, Karim Ayubi Awaz, Zahra Ahmadizadeh, Mona Simin Qalam, and Seyed Abolfazl Tohidast; Research and review: Karim Ayubi Awaz and Zahra Azani.

Conflict of interest
 The authors declared no conflict of interest.

Acknowledgments
We thank and appreciate the cooperation of all parents participating in this study, medical centers in coordinating and collecting information related to this study, and the student Research Committee of the University for approving and financially supporting this plan. 


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