We invited all 32 NM and NMr patients over 16 years of age (16–90) resident in Finland and included in the Folkhälsan Research Center registry (Fig. 1), which, to our knowledge, includes the vast majority of NM and NMr patients from all University Hospital districts in Finland. The invited patients were from 26 families. The information letters and consent forms to be signed were sent as letters to the home addresses of the patients.

Invited patients: ambulatory nemaline myopathy (NM), non-ambulatory NM patients, and patients with NM related disorders; participants and non-responders, and the age range of the invited persons. M males, F females

Where possible, the items for the survey were selected from previously published and/or validated questionnaires. The main item source was the Patient-Reported Outcomes Measurement Information System (PROMIS®) [27,28,29]. In addition, the National FinSote2019 Survey [32], and a survey designed for people with skeletal dysplasia in Finland (LYHTY) [33, 34] were used. The research group (RG) designed questions when suitable questions could not be found in existing surveys. These were questions about medical conditions diagnosed by a medical doctor, and questions related to mobility: walking ability on different surfaces, usage of mobility aids or wheelchair. Questions concerning the impact of the COVID-19 pandemic on functioning were, also, addressed by the RG. In addition, the survey included open text fields for optional comments after each subject field. The panelists selecting the PROMIS® items were five persons with NM and RG members, following the validation procedure described in [35]. Questions from other surveys were selected by the RG.

The survey contained eight modules, each containing questions, which in turn consist of separate items (in parentheses the number of items; the source of the item): (1) Background questions (7; 4 generic (subjects characteristics), 2 FinSote2019, 1 RG), (2) Rehabilitation services, other services, aids (22; 14 FinSote2019, 4 LYHTY, 4 RG), (3) Physical functioning (22; 20 PROMIS®, 2 LYHTY), (4) Social functioning (10; PROMIS®), (5) General Health (10; PROMIS®), (6) Pain, Fatigue and Sleep (12; PROMIS®), (7) Mental well-being (5; PROMIS®) (8) Questions related to the muscle disorder and other medical conditions and treatments (12; 1 generic, 1 FinSote2019, 5 LYHTY, 5 RG).

Most items addressing the self-reported functioning were selected from validated PROMIS® questionnaires. The following PROMIS® instruments were used (in parentheses the number of items selected per instrument): Global health (Physical (5), Mental (5)), Physical function (24), Fatigue (4), Sleep Disturbance (4), Satisfaction with Social Roles and Activities (8), Pain Interference (3), Emotional Distress—Depression (3), Ability to Participate in Social Roles and Activities (2), Emotional Distress—Anger (1) and Anxiety (1).

The final questionnaire was created using Webropol, and the subjects could fill it out either electronically or on paper. Any uncertainties or discrepancies in the responses were clarified with the participant by telephone by the first author.

Each five-point Likert scale variable (item) was linked to an International Classification of Functioning in Disability and Health (ICF)-category [30] using the ICF linking rules [36]. For calculating the sum variables, the responses were converted as follows: point 1 indicated “no problems” and point 5 indicated “a lot of problems”/ “unable to”; in other words, a higher number indicated more poor functioning.

The ICF blocks and chapters were fitted to form sum variables to minimize the number of items. The following ICF-based categories were formed (the number of items included per category in parentheses); b1 Mental functions: fatigue (5), sleep (4), emotional distress (6), b2 Sensory functions and pain: muscle pain (3) and joint pain (1) and sensation of pain (4), b7 Neuromusculoskeletal and movement-related functions: muscle functions (2), d2 General tasks and demands: carrying out daily routine (1), d4 Mobility: changing and maintaining body position (6), hand and arm use (8), walking and moving around using equipment (3), moving around within a home (1), d4 Selfcare: dressing, toileting, washing oneself (7), d6 Domestic life: acquisition of goods and services (2), doing house work (1), leisure time at home (1), d7 Interpersonal interactions and relationships (2), d8 Major life areas: work (1), d9 Community, social and civic life, e1 Products and technologies: assistive products (1), assistive products for mobility (3), e2 Natural environment: climate (2), and the impact of Covid-19 pandemic to fatigue, sleep, emotions, pain, general health, physical functioning, daily living, social life, applying health and social services, access to health and social services. The items addressing the ability to walk and move around using equipment included the use of mobility aids (a self-propelled or electric wheelchair, or a walker). The formed variables were sorted into groups: physical, psychological, and social functioning, and environmental factors affecting physical functioning. The impact of COVID-19 pandemic to the self-reported functioning was processed as its own entirety.

The internal consistencies of the sum variables formed were tested using Cronbach’s alpha [37]. If Cronbach’s alpha was below 0.7, the item(s) not computationally belonging to the sum variable was removed from the group and analyzed separately. The Cronbach’s alphas of the final sum variables formed varied from 0.73 to 0.96.

ICF categories for the areas of functioning assessed, the source of the item used (and number of items), and Cronbach’s α-value for the sum variables are presented in Additional file 1.

PROMIS item banks contain a collection of items, each measuring the same domain. This enables a selection of single items to be used to study the domain [38]. The PROMIS instrument is based on Item Response Theory (IRT) and a software application utilizing it. Health Measures Scoring Service (HM-SS), is developed to convert the raw scores (on a Likert scale of 1 to 5) of the responses to standardized T-scores for each instrument [39]. In the PROMIS T-score metric, 50 is the mean of a relevant reference population, and the standard deviation (SD) is 10 in a reference population (usually the U.S. general population). Standardized scores for the Finnish population are lacking, and therefore the T-scores were calculated using the standard scores for the US population. A standardized T-score was calculated using a scoring service [40]. The minimum requirement of the items to calculate the T-scores for the selected instruments used in this survey was four. Subsequently, the instruments for Global health, Physical function, Fatigue, Sleep Disturbance, and Satisfaction with Social Roles and Activities were scored, while Ability to Participate in Social Roles and Activities, Emotional Distress—Anger, and Anxiety were not scored. They were processed according to their ICF category-based sum variable labelled as “emotional functioning”, as described above. PROMIS scoring system includes the levels for the functioning based on T-scores of the reference and validation populations [41]. For example, for the Physical Functioning, a T-score above 45 means “within normal limits”, 40–45 “mild decline”, 30–40 “moderate decline” and below 30 “poor” physical functioning.

The responses of the study participants were analyzed using Excel and IBM SPSS Statistics 28.0.

The participants’ responses were reviewed according to groups; responses of NMr (8, 40%), ambulatory NM (8, 40%), and non-ambulatory NM (4, 20%) patients. In addition, the groups under and over 50 years of age, ambulatory (both NMr and NM patients), and NM patients (including ambulatory and non-ambulatory patients) were reviewed.

We calculated percentages of the responses of each ICF-based variable (i.e., how many percent of the responses in each group were 1 (no/never problems), 2 (little/rarely problems), 3 (some/sometimes problems), 4 (much/often problems) and 5 (very much/unable to/always problems), the mean values, and the standard deviations of the responses.

The PROMIS-based T-scores with minimum and maximum values were processed similarly.

The survey included open text boxes for background questions and for possible additional comments the participants wanted to add or raise after each module. These responses were reviewed separately, and they can be utilized for modifying the survey for possible future studies.