Parental illness intrusiveness in parents of children with neuromuscular disorders

Abstract

Background:

Pediatric neuromuscular diseases (NMDs) do not only affect patients themselves, they also exert an impact on parents. However, the impact that parents experience on their own personal lives remains largely understudied.

Objective:

This study introduced the construct of parental illness intrusiveness in a NMD population by addressing two objectives. First, to increase our insight in the levels of parental intrusiveness in the NMD population, these parents were compared to parents of youth with type 1 diabetes (T1D). Second, we aimed to increase our understanding of parental illness intrusiveness within the NMD sample by exploring its associations with parental demographical characteristics, parental depressive symptoms and quality of life, and disease- and child characteristics.

Methods:

A total of 56 parents of youth with a NMD (aged 12–25) and a 2:1 matched sample of parents of youth with T1D completed questionnaires on parental illness intrusiveness, parental depressive symptoms, parental quality of life, and perceived patient physical functioning. For Objective 1, ANOVAs were conducted to compare parents in the NMD sample to parents in the T1D sample. For Objective 2, ANOVAs and correlational analyses were used.

Results:

First, parents in the NMD sample reported significantly more illness intrusiveness, but not depressive symptoms as compared to parents in the T1D sample. Second, parental illness intrusiveness correlated positively with parental depressive symptoms and perceived patient physical impairment, and negatively with parental quality of life.

Conclusions:

Compared to parents of a child with T1D, parents in the NMD population may experience more impact of their child's disease in their personal life. Parents of youth with higher physical impairment may be particularly at risk for experiencing difficulties among a wide array of personal life domains.

Keywords

neuromuscular disorders parental illness intrusiveness parental psychological wellbeing adolescence emerging adulthood

Introduction

Neuromuscular disorders (NMDs) entail a heterogeneous group of diseases that are characterized by a deficit in the peripheral nervous system which causes impaired motor functioning.^1,2 Most individual NMDs have a prevalence rate of 1–10 in 100,000, yet when considered as a group, their prevalence is estimated around 100–300 in 100,000.¹ Although they generally cannot be cured, their course and survival rates have drastically improved over the last years due to innovative disease-modifying treatments.²

Not only throughout childhood, but also during adolescence and emerging adulthood, patients with pediatric NMDs often need to rely on their caregivers for (physical) care. For progressive NMDs (e.g., Duchenne muscular dystrophy), this need for care and support in daily life even tends to increase throughout adolescence and young adulthood as physical functioning gradually deteriorates.³ The caregiving role is most often adopted by parents and, consequently, the personal lives of these parents can be profoundly impacted by the disease as well.^4,5 Yet, parents’ unique illness-related experiences and the effect of the disease on their own personal lives remains largely understudied. Earlier work has shown that caregivers of patients with NMDs are at increased risk to experience a multiplicity of psychosocial difficulties and/or high caregiver burden.^4,6 Psychological distress indeed seems to be more prevalent in parents caring for a child with a NMD as compared to the general population.^4,7,8 Furthermore, different studies have shown that parents can feel impacted in various domains of their own personal life, such as leisure activities, work life, or financial situation.^4,5,9

The present study aimed at obtaining a better understanding of illness-related experiences in parents of adolescents and young adults with NMDs. In doing so, the construct of parental illness intrusiveness was introduced and investigated. Parental illness intrusiveness can be defined as parents’ subjective feelings that caring for their child with a medical condition hinders them in different domains of their own personal life, such as social relationships, leisure activities, finances, or civic involvement.^10,11 It captures unique and possibly understudied aspects of caregivers’ experiences in the context of chronic illness. As such, it may provide a more nuanced perspective on their functioning as compared to more general well-being indicators such as depressive symptoms.¹² In other illness populations such as juvenile rheumatic disease,^10,13 type 1 diabetes¹⁴ and sickle cell disease,¹⁵ its relevance has been established by providing insight in parental experiences of daily life restrictions related to the illness of their child.

Objective 1

In the first objective, we aimed at increasing our insight in the uniqueness of parental illness intrusiveness in parents of a child with a NMD by comparing them to parents of a child with type 1 diabetes (T1D). Whereas there exists ample research on parental illness-related experiences in T1D,^14,16,17 this research area has been largely understudied within the NMD population. Comparing parents in a NMD population to parents in a T1D population would thus increase our understanding of the relative impact that parents caring for a child with a NMD experience in their personal life. In this study, the two samples were compared on parental illness intrusiveness and parental depressive symptoms.

We expected parents in the NMD group to experience higher levels of parental illness intrusiveness than parents in the T1D group. According to general developmental theories, youth become more independent from their parents throughout adolescence and emerging adulthood.¹⁸ Youth with T1D gradually increase in responsibility over their diabetes management,¹⁹ possibly resulting in a lower impact on parents’ personal lives as their child grows older. Youth with NMDs often continue to rely on their parents for support and care because of their physical impairments. For some, these care needs may even increase as the disorder progresses. Consequently, for parents of youth with a NMD, the impact of the illness on their own personal lives may remain relatively high.²⁰

With respect to parental depressive symptoms, there seems to be a general psychological vulnerability in parents of children among various chronical health conditions.²¹ Parents of children with progressive diseases, such as Duchenne muscular dystrophy, may be particularly at risk for experiencing depressive symptoms.^8,21 However, given that the current NMD population included multiple progressive and non-progressive NMDs, we did not formulate any specific hypotheses on this matter.

Objective 2

The second objective focused in-depth on the NMD sample and explored how parental illness intrusiveness was associated with demographical and psychological variables in parents, and to relevant child and disease variables. First, in parents, we explored whether parental illness intrusiveness would be associated with parental demographical characteristics (i.e., parental relationship status and employment status) and parental psychological well-being indicators (i.e., depressive symptoms and overall quality of life). Associations with demographical characteristics were explored without formulating concrete expectations. Concerning parental well-being, we expected that parental illness intrusiveness would correlate positively with parental depressive symptoms, similar to what has been found in other illness populations.^10,13,14 In a former study in caregivers of young patients with Duchenne muscular dystrophy, parental caregiving burden was correlated with lower parental quality of life.²² Consequently, we anticipated that parental illness intrusiveness would correlate negatively with overall quality of life in parents.

Second, associations between parental illness intrusiveness and the following child- related variables were investigated: perceived physical functioning, disease course (i.e., stable, slowly progressive, progressive), child gender, and child age. We anticipated that parental illness intrusiveness would be higher in parents of youth with higher levels of perceived physical impairment because those patients would need to rely more on their caregivers for help and support.²⁰ Associations with patient age could be more complex, possibly also depending on other factors such as, for instance, the progressive nature of the disease. Therefore, we did not formulate specific expectations about patient age or disease course. Associations with child gender were also explored without formulating specific expectations.

Materials and methods

Participants and procedure

Data for the present study originated from a larger study on the psychosocial and cognitive development of children and youth with NMDs and the psychosocial functioning of their parents.²³ Participants were selected from the database of the Neuromuscular Reference Center for children at University Hospitals Leuven. Dutch speaking patients between 12 and 25 years with a NMD and one caregiver were invited to complete questionnaires between January 2019 and November 2020. An informed consent form was signed either by patients (aged 18 or more) or by parents (for minors). The study was approved by the ethics research committee of University Hospitals Leuven, Belgium (S57182). Of the 110 eligible patients, 59 patients participated (Response rate = 54%). The current study used data of 56 participating parents (Data from n = 3 were excluded from analyses to avoid data interdependencies).

To address Objective 1, parents of youth with NMDs were compared to parents of youth with T1D. The T1D study sample originated from the baseline measurement of a longitudinal questionnaire study. The total sample consisted of 463 mothers and 384 fathers (see Oris et al.²⁴ and Prikken et al.¹⁴). Every parent of a patient with a NMD was matched to two parents of patients with T1D on parental gender, parental age and child age. If no exact match was available, nearest neighbor matching was applied. Demographical and disorder-related information of parents and patients for both the NMD and the T1D sample can be found in Table 1.

Table 1.

Demographic and clinical characteristics of the NMD and T1D samples.

	NMD N = 56	T1D N = 112
Parent
Gender
Female	43 (76.8%)	86 (76.8%)
Male	13 (23.2%)	26 (23.2%)
Age (SD)	45.96 (4.99)	45.96 (4.99)
Living situation
Married or living together	45 (80.4%)	102 (91%)
Not married or living together	11 (19.6%)	10 (8.9%)
Employment status
Employed	46 (82.1%)	92 (82.8%)
Not employed	10 (17.9%)	19 (17.1%)
Educational level
≤ Secondary school	22 (39.3%)	52 (47.7%)
≥ Higher education	34 (60.7%)	57 (52.2%)
Patient
Gender
Female	16 (28.6%)	51 (47.2%)
Male	40 (71.4%)	57 (52.8%)
Age (SD)	16.02 (2.91)	16.50 (2.36)
Age at diagnosis (SD)	4.27 (3.07)	8.59 (4.30)
NMD Diagnosis
Arthogryposis multiplex congenita	2 (3.6%)	NA
Axonal motor neuropathy	1 (1.8%)	NA
Limb girdle muscular dystrophy	5 (8.9%)	NA
Bethlem myopathy	1 (1.8%)	NA
Charcot-Marie-Tooth disease	4 (7.1%)	NA
Collagen 6 myopathy	1 (1.8%)	NA
Congenital myopathy	5 (8.9%)	NA
Duchenne muscular dystrophy	23 (41.1%)	NA
Multi-minicore myopathy	1 (1.8%)	NA
Friedreich ataxia	1 (1.8%)	NA
TTF1 mutation	1 (1.8%)	NA
Myotonic Dystrophy, type 1	2 (3.6%)	NA
Paroxysmal nonkinesigenic dyskinesia	1 (1.8%)	NA
Spinal muscular atrophy type 2	7 (12.5%)	NA
Spinocerebellar ataxia	1 (1.8%)	NA
NMD Physical Disease course
Stable	12 (21.4%)	NA
Slowly progressive	14 (25.0%)	NA
Progressive	30 (53.6%)	NA

Note. NA = Not Applicable.

Measures

Parental illness intrusiveness

Both in the NMD and the T1D sample, parents completed the Illness Intrusiveness Scale—Parent Version (IIS-P).¹⁰ They rated how much they felt that the disease of their child affected the following 13 life domains: work, active recreation, passive recreation, financial situation, relationship with partner, sex life, family relations, other social relations, self-improvement/self-expression, religious expression, community and civic involvements, health, and diet. Responses varied from 1 (not very much affected) to 7 (very much affected). The 13 items were translated to Dutch using the back-translation procedure.²⁵ Higher sum scores indicated more parental illness intrusiveness. Cronbach's alphas were .91 in the NMD sample and .88 in the T1D sample.

Parental depressive symptoms

In both samples, caregivers completed the Center for Epidemiologic Studies Depression Scale (CES-D).²⁶ This 20-item questionnaire screens for depressive symptoms during the past week. Responses vary from 0 (rarely or none of the time—less than 1 day) to 3 (most or all of the time—3 to 7 days). Higher scores indicated more depressive symptoms. Cronbach's alphas were .88 in the NMD sample and .90 in the T1D sample.

Parental overall quality of life

In the NMD sample, parental overall quality of life was assessed using one item rated on a VAS-scale ranging from 0–10.

Patient physical functioning

In the NMD sample, two measures provided an indication of perceived physical functioning. First, the physical subscale of the PedsQL—Neuromuscular Module—Parent Report²⁷ assessed illness-related quality of life by use of 17 items. Items were rated on a 5-point Likert-scale from 0 (never) to 4 (almost always). Items were linearly transformed to a 0 to 100 scale (0 = 100, 1 = 75, 2 = 50, 3 = 25, and 4 = 0) so that higher scores indicated better perceived physical functioning. Cronbach's alpha was .90. Second, the ACTIVLIM²⁸ is a questionnaire tapping into activity limitation. The 22 items were rated as 0 (impossible), 1 (difficult), or 2 (easy). The lower the total sum score, the more physical limitations were experienced.

Patient medical information

Medical records were consulted to verify specific diagnosis, and time since diagnosis.

Plan of analysis

Hypotheses and analysis plans were preregistered at Open Science Framework (https://osf.io/t47an). For Objective 1, two analyses of variance (ANOVAs) were conducted with parental illness intrusiveness and parental depressive symptoms as dependent variables, respectively, and the disease population as independent variable. After running the preregistered analyses, post-hoc additional analyses were conducted to focus on the individual items of the IIS-P. Using MANOVA, it was tested whether the individual items would differ between the NMD and the T1D sample. In case of a significant multivariate effect (i.e., Wilks’ Lambda), univariate effects were interpreted as well.

Objective 2 addressed parental illness intrusiveness within the NMD sample. First, associations between parental illness intrusiveness and parental demographic and well-being indicators were examined using ANOVAs and bivariate correlations. More specifically, two ANOVAs explored whether parental relationship status or employment status would be predictive of parental illness intrusiveness (ANOVAS were used instead of cross-tabulations which were described in the preregistration because ANOVAs were considered more appropriate for answering the current research question.). Bivariate Pearson correlations calculated associations between parental illness intrusiveness on the one hand, and parental depressive symptoms and parental quality of life on the other.

Second, associations between parental illness intrusiveness and child- and illness characteristics were again examined using both ANOVAs and bivariate correlations. Two ANOVAs were conducted, one for child gender and one for the progressive nature of the disease (stable/slowly progressive/progressive) in predicting parental illness intrusiveness. Bivariate Pearson correlations were calculated to assess associations between parental illness intrusiveness on the one hand, and child age and physical functioning (i.e., PedsQL and ACTIVLIM) on the other. For ANOVAs, partial η² provided information on effect sizes. Effect size was considered small when η² < .05, medium when .05 < η² < .13 and high when η² > 0.14. Correlations were interpreted as low when r < .40, medium when .40 < r < .70 and high when r > .70.²⁹

Lastly, we also conducted some additional analyses at the item-level of the IIS-P. By use of bivariate Pearson correlations, associations between the different items of the IIS-P and the other study variables were explored to assess whether and how the impact among different life domains would be associated with patient physical functioning, parental quality of life, or parental depressive symptoms.

Results

Objective 1

The total score of parental illness intrusiveness significantly differed between the two samples [F(1165) = 10.24, p = .002, η2 = .06], with parents in the NMD sample reporting higher levels of parental illness intrusiveness than parents in the T1D sample. Parental depressive symptoms, on the other hand, did not significantly differ between the two study samples [F(1163) = 1.01, p = .32, η2 = .01] (As there was no exact 2:1 match on parental and child age, the ANOVAs and MANOVA were repeated with parental and child age as covariates. Equal results were obtained with respect to the effect of disease group.). Mean scores for all study variables and results of the ANOVAs can be found in Table 2. With respect to the additional analyses, the multivariate effect comparing the individual items of the IIS-P between the NMD and the T1D sample was significant [Wilks’ Lambda = .55; F(13,139) = 8.82, p < .001, η² = .45]. When looking at the individual items, differences between the two samples were statistically significant for almost all items, except for health and religious expression. Parents in the T1D sample reported higher scores on the diet item. For the remainder of the items, parents in the NMD sample reported significantly higher levels of parental illness intrusiveness.

Table 2.

Descriptive statistics and ANOVAs comparing the NMD and T1D study sample.

Variable	NMD Mean (SD)	T1D Mean (SD)	F(df1, df2)	η²
TOTAL SCALE SCORES
IIS-P	37.78 (17.73)	30.04 (13.05)	10.24 (1165)**	.06
CES-D	9.77 (7.70)	8.50 (7.53)	1.01 (1163)	.01
Parental overall QoL	7.21 (1.51)	NA
PedsQL-NM Physical subscale	57.62 (21.30)	NA
ACTIVLIM	15.60 (14.12)	NA
IIS-P INDIVIDUAL ITEMS			Df = (1151)
Work	3.41 (2.24)	2.53 (1.62)	7.57**	.05
Active recreation	3.90 (2.15)	2.48 (1.76)	18.69***	.11
Passive recreation	2.55 (1.83)	1.83 (1.38)	7.39**	.05
Financial situation	3.14 (1.95)	2.46 (1.68)	4.93*	.03
Relationship with partner	3.37 (2.08)	2.58 (1.64)	6.48*	.04
Sex life	2.67 (1.96)	1.66 (1.15)	16.03***	.10
Family relations	3.16 (2.19)	2.04 (1.45)	14.19***	.09
Other social relations	3.35 (2.04)	2.15 (1.51)	16.47***	.10
Self-improvement/expression	3.20 (2.23)	2.16 (1.57)	11.07**	.07
Religious expression	1.57 (1.46)	1.57 (1.14)	.00	.00
Community/civic involvements	3.34 (2.15)	2.27 (1.51)	14.81***	.09
Health	2.55 (1.87)	2.65 (1.82)	.10	.00
Diet	1.88 (1.62)	3.67 (1.94)	31.54***	.17

Note. *p < .05; **p < .01; ***p < .001

Objective 2

First, parental employment status (employed or not) and parental relationship status (living together with a partner or not) did not significantly predict parental illness intrusiveness [F(1,53) = 3.52, p = .066, η² = .06 and F(1,54) = 0.02, p = .878, η² = .00, respectively]. Associations between parental illness intrusiveness on the one hand, and parental depressive symptoms and parental quality of life on the other, were significant. As shown in Table 3, a positive correlation was found with parental depressive symptoms and a negative correlation was found with parental quality of life.

Table 3.

Correlational analyses between the IIS-P item-scores and other study variables.

IIS-P items	Activity limitation (ACTIVLIM)	Physical subscale (PedsQL-NM)	Patient age	Parental quality of life	Parental depressive symptoms (CESD)
Work	−.28*	−.65***	−.05	−.32*	.42**
Active recreation	−.53***	−.42**	.13	−.10	.19
Passive recreation	−.50***	−.50**	.03	−.08	.38**
Financial situation	−.28*	−.44**	−.00	−.24	.25
Relationship with partner	−.33*	−.24	−.04	−.25	.30*
Sex life	−.33*	−.44**	−.07	−.23	.39**
Family relations	−.21	−.31	−.03	−.18	.34*
Other social relations	−.44**	−.46**	−.00	−.08	.39**
Self-improvement/expression	−.38**	−.41*	.19	−.22	.34*
Religious expression	−.09	−.40*	.02	−.03	.37**
Community/civic involvements	−.52***	−.39*	.12	−.21	.32*
Health	−.41**	−.60***	.28*	−.27*	.39**
Diet	−.33*	−.55***	.16	−.19	.33*
TOTAL SCORE IIS-P	−.52***	−.65***	.07	−.27*	.48***

Note. *p < .05; **p < .01; ***p < .001.

Second, child gender and disease course did not significantly predict parental illness intrusiveness [F(1,54) = 2.21, p = .142, η2 = .04 and F(2,53) = 2.63, p = .081, η2 = .09, respectively]. As shown in Table 3, bivariate correlations were significant between parental illness intrusiveness and patient perceived physical functioning as indicated by a negative correlation with the PedsQL physical subscale and the ACTIVLIM. Bivariate correlations between parental illness intrusiveness and patient age were non-significant.

Concerning the additional analyses which explored associations between the individual IIS-P items and perceived patient physical functioning, multiple correlations occurred that were interpreted as being at least moderately strong. Except for the items on family relations and relationship with partner, moderate correlations were found with scores on the ACTIVLIM, the PedsQL physical subscale, or both. Furthermore, most of the IIS-P items correlated positively with parental depressive symptoms, again with multiple moderate correlations. Most associations with parental overall quality of life were either non-significant or interpreted as low correlations.

Discussion

This was the first study to introduce the construct of parental illness intrusiveness in parents of youth with NMDs. By addressing two study objectives, relevant new insights were gained that contribute to a deeper and more nuanced understanding of parental illness-related experiences in parents caring for adolescent and emerging adults with NMDs.

The first objective demonstrated that parents in the NMD sample reported higher levels of parental illness intrusiveness as compared to parents in the T1D sample, whereas differences in parental depressive symptoms were non-significant. With respect to parental illness intrusiveness, the findings were in line with expectations and may thus provide further evidence for our hypothesis that the physical dependence of patients with a NMD can result in a higher impact on parental personal lives. When looking at the individual life domains as assessed by the IIS-P, we found that parents in the NMD sample experienced a higher impact of the disease among almost all life domains except for the life domain of diet, for which the opposite effect occurred. This latter finding may be explained by the dietary restrictions being a core part of the treatment of T1D,¹⁹ which, in turn, could also impact parental dietary intake.

Depressive symptoms, on the other hand, did not differ significantly between the NMD and the T1D study population. When comparing various disease populations, a former meta-analysis concluded that parents of children with NMDs would be at risk for experiencing elevated depressive symptoms, and particularly so for progressive NMDs.²¹ Hence, although the current findings do not fully replicate the findings of Pinquaert and colleagues, they rather seem to fit in with their general conclusion that all parents of children with chronical conditions may be at higher risk for experiencing depressive symptoms.²¹

The second objective specifically focused on parental illness intrusiveness in the NMD sample. First, in parents, parental illness intrusiveness did not differ for parental employment status and relationship status. Related work has also found that parental burden or distress was not significantly associated with parental relationship status⁷ or frequency of vocational activities.⁴ Higher parental illness intrusiveness co-occurred with relatively higher levels of parental depressive symptoms and a lower overall parental quality of life. These findings confirmed our expectations, fitting in with related research in a NMD population as well.²² It should be noted, however, that the current results do not allow for assessing directionality of effects. It seems plausible that there would be a mutual interplay among parental quality of life, parental depressive symptoms and parental illness intrusiveness over time, with these variables possibly reinforcing one another.^30–33 As longitudinal research targeting these issues is largely absent within NMDs, this would provide an important next step in improving our understanding of parents’ experiences.

Second, concerning associations with child- related variables, child gender, child age and disease course were not significantly associated with parental illness intrusiveness. It would, however, be useful for future work to further look into these associations because interaction effects may occur. For instance, in progressive NMDs, it seems plausible that parental illness intrusiveness would increase when children grow older, whereas this may not hold for children with stable or non-progressive NMDs. Importantly, the current study indeed revealed that higher levels of perceived physical impairment in the child correlated with higher parental illness intrusiveness, indicating a more profound impact on parents’ personal lives among a wide array of life domains. This was found not only for life domains that have received former research attention such as vocational activities or social relationships,^4,9,20,34 but also for more broader and general aspects of parents’ personal functioning such as health and self-expression. It seems important to discuss such themes as well in order to provide adequate psychological support for these parents.

Although the obtained results testify to the relevance of studying parental illness intrusiveness and its assets in this NMD population, some study limitations need to be mentioned. First, the sample size was rather small and only included Dutch-speaking participants of families treated at University Hospitals Leuven. Generalizability of the findings may thus be limited. Second, the NMD population is a heterogeneous group encompassing a large amount of diseases with varying severities and prognoses. Because of the rather small sample size, we were not able to differentiate among the individual diseases. Our choice of differentiating between stable, slowly progressive, and progressive diseases could only partially account for this issue. Third, the large majority of parents were mothers, whereas fathers were underrepresented. This represents a large gap in the broader literature as well and it is widely encouraged to proactively target fathers in research efforts and clinical care.³⁵ Fourth, the current study almost exclusively used data from self-report questionnaires except for the patient characteristics of disease course and patient gender. Although self-report measures are suited for measuring internal subjective experiences such as parental illness intrusiveness and depressive symptoms, it could also induce shared method variance. In addition to the current quantitative approach, mixed-method approaches should be considered in future work as well, given that parental experiences and perspectives might be better understood when quantitative and qualitative data are combined. Fifth, the current study mainly focused on the negative impact of caring for a child with a chronic condition. This negative approach should be complemented by a focus on more positive illness-related experiences.³⁶

To conclude, the present study provided further insight in the wide-ranging impact that a pediatric NMD can have on parental personal lives. Compared to parents of a child with T1D, parents in a NMD population experienced more impact of the disease among a wide variety of life domains, which may be partially explained by the higher physical care needs of patients with NMDs. Indeed, particularly parents of youth with higher physical impairment seemed to be at risk for experiencing difficulties in their personal life. Above and beyond commonly addressed domains such as vocational activities or leisure time, several other and less-studied life domains were found to be impacted by the caregiving role as well, such as community and civic involvement or self-expression. By putting attention to all of these life domains, the current study further testified to the relevance of the IIS-P questionnaire in this population. Using the construct of parental illness intrusiveness in research and clinical work may be important to identify the challenges parents are confronted with and provide those parents in need with adequate psychosocial support. Given that socio-ecological theories consistently underscore mutual associations between parental and youth functioning,^37,38 parental illness intrusiveness should not be overlooked when studying family functioning in families confronted with pediatric NMDs.

Footnotes

Acknowledgements

LDW is member of the European Reference Network for Rare Neuromuscular Diseases (ERN EURO-NMD).

ORCID iDs

Sofie Prikken

Sam Geuens

Elise Van Laere

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by Duchenne Parent Project Netherlands and Roche SA/NV. Neither of these organizations were involved in the study design, data acquisition, data analyses, or manuscript preparation.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data availability statement

The data that support the findings of this study are available on request from the corresponding author, S.P. The data are not publicly available due to privacy and ethical restrictions.

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