Visual functions, ocular characteristics and visual quality of life in patients with homocystinuria

ABSTRACT

Background

Homocystinuria (HCU) is a rare metabolic disease that affects many organs, including the eyes. Aims: to assess visual functions, ocular characteristics, visual quality of life and time from the onset of ocular manifestations to HCU-diagnosis in patients with HCU.

Material and methods

Eighteen patients underwent ophthalmological examinations and visual quality of life questionnaires.

Results

Best corrected decimal visual acuity was median 1.0 (range amaurosis - 1.3) right eye and 1.0 (range amaurosis -1.3) left eye. Five patients presented with severe myopia as first HCU manifestation, duration to HCU diagnosis was mean 13.6 years (range 2-25). Two patients had suffered ectopia lentis as first HCU manifestation, HCU diagnosis was established mean 8.0 years (range 7-9) later. One patient had suffered both from thrombosis and ectopia lentis prior to diagnosis. Another four patients suffered thromboembolic events before diagnosis. Median VFQ-25 composite score was 93 (68-98).

Conclusions

The prevalence of myopia, ectopia lentis and monocular blindness was high in HCU-patients, which was reflected in their visual quality of life. Diagnosis was often delayed after the first ocular manifestation, increasing the risk of other severe non-ocular complications.

KEYWORDS:

• Homocystinuria
• myopia
• ectopia lentis
• optical coherence tomography
• ultra-widefield fundus photography
• quality of life

1. Introduction

Classic homocystinuria (HCU) is a rare metabolic disease in which severe eye manifestations are common (1,2). The autosomal recessive disease is caused by abnormal metabolism of the amino acid homocysteine (Hcy), due to pathogenic variants in the CBS gene. The CBS gene codes for the vitamin B₆-dependent enzyme cystathionine beta-synthase (CBS), which converts homocysteine (Hcy) to cystathionine. Other defects in homocysteine metabolism includes the remethylation disorders (1,3).

The worldwide prevalence of HCU has been estimated as 1:200,000 to 1:335,000 (4), with higher estimated prevalence in Ireland (1:67,000) (5), Italy (1:55,500) (5) and Qatar (1:1800) (6). HCU was added to the Swedish screening program for newborns in 2010 (7), but all the patients included in this study were born prior to its introduction.

Typical non-ocular manifestations of HCU include skeletal ones, which can impact bone mineral density and cause a marfanoid body structure (8,9), an increased risk of thrombosis including sinus thrombosis (10,11), and nervous system manifestations that include varying degrees of intellectual disability, anxiety, depression, obsessive-compulsive disorders, and personality disorders (12).

Ocular manifestations may aid early diagnosis. Ectopia lentis (subluxation or dislocation of the crystalline lens secondary to dysfunction or disruption of zonular fibers) and high myopia (≤-6 Diopters) are among the most common manifestations associated with HCU (2). Other ocular manifestations include retinal degeneration and detachment (13), occlusion of the retinal vessels (14) and glaucoma (15). The underlying pathophysiology and cause of ocular manifestations is not fully known. However, one theory is that a local deficiency of cysteine, a semi-essential amino acid that counteracts protein precipitation (16), leads to the thickening and disruption of zonulae fibers that normally provide a suspensory system for the lens. This results in ectopia lentis (2). Even though ocular manifestations are common in HCU, research on ocular findings in patients diagnosed with HCU is scarce (2). Few studies have used modern devices like optical coherence tomography (OCT), and no studies have used ultra-widefield photography (UWFI) with autofluorescence to examine the retina in patients with HCU. OCT and UWFI can provide valuable information regarding retinal changes, for example, retinal vessel occlusions (17–22).

Treatment for HCU is aimed at lowering the concentration of Hcy. Patients with HCU require lifelong treatment and follow-up to maintain acceptable Hcy levels (23), which plays a crucial role in preventing severe manifestations (2). The most important factor when designing a treatment strategy is whether the patient carries a variant in the CBS gene that is vitamin B₆ responsive. B₆ non-responsive patients are more challenging to treat, and a combination of betaine and a methionine-restricted diet is often used (23). Vitamin B₆ non-responsive patients typically present with more severe manifestations than vitamin B₆-responsive patients (2,24).

The objectives of the current study were to assess visual outcomes and anterior and posterior segment findings in patients with HCU, grouped by B₆ responsiveness. Further objectives were to study the time that elapsed between the onset of visual or ocular problems and diagnosis and the visual quality of life in patients with HCU.

2. Material and methods

Patients who participated in this regional clinical cohort study were recruited from the Department of Endocrinology at Karolinska University Hospital. The inclusion criterion was the biochemical diagnosis of homocystinuria and homozygous or compound heterozygous pathogenic variants in the CBS gene. A total of 19 patients fulfilled the inclusion criterion and 18 patients consented to participation. Information regarding patients’ disease manifestations, sex, age, and prior visits to ophthalmologists was obtained through medical records. The patients were grouped by responsiveness to vitamin B₆ using the general guideline by Morris et al. (2). B₆-responsiveness was defined as a total plasma concentration of homocysteine (tHcys) ≤50 µmol/L after treatment with pyridoxine was initiated. Partial B₆-responsiveness was defined as having a tHcys of ≥50 µmol/L after starting treatment with pyridoxine, but a reduction of tHcys by >20% from the baseline. Patients with a reduction of tHcys by <20% were defined as B₆ non-responsive.

All patients in the study provided informed consent. This study was completed in accordance with the Declaration of Helsinki.

Clinical ophthalmological examinations were performed at St. Erik Eye Hospital by the same ophthalmologist (KTF). They included the medical history of the patient’s subjective symptoms, such as dry eyes and light sensitivity, and the assessment of best-corrected visual acuity (BCVA) (Konstantin Motakis Ortho KM, Lund, Sweden), ocular range of motion and ocular alignment. Refractive errors were quantified using the autorefractor (Triton; Topcon Medical Systems, Tokyo, Japan) in cycloplegia. The anterior and posterior segments of the eye were assessed using a biomicroscope. The intraocular pressure was assessed using iCare (iCare Finland OY, Vanda, Finland).

Mild myopia was defined as 0 diopters (D) to −1.5 D, moderate myopia as −1.5D to −6D, and severe myopia as ≤-6D according to the guidelines by Fredrick (25).

The Topcon SS-OCT (Triton; Topcon Medical Systems, Tokyo, Japan) was used to collect OCT and color fundus images. Optos UWFI (Optos, Dunfermline, Scotland) was used to obtain wide field photographs of the retina. The same retinal specialist (DE) assessed all images.

The VFQ-25, a questionnaire consisting of 25 items designed by the US’ National Eye Institute (NEI) and validated for patients with chronic eye disorders (26,27), was used to evaluate quality of life regarding vision and health. The questionnaire has 12 sub-scales: distance activities, near activities, color vision, ocular pain, peripheral vision, driving, general health, general vision, and vision-specific sub-scales; mental health, social functioning, dependency, and role difficulties. Each sub-scale was scored, and a general VFQ-25 score was estimated, although the general health sub-scale was excluded. VFQ-25 scores were compared in the groups categorized by B₆ responsiveness, as well as in groups categorized by surgery.

Student’s T-test was used to compare age at diagnosis in patients grouped by B₆ responsiveness.

3. Results

3.1. Demographic data and presentation

A total of 18 patients were included in the study, seven male patients and 11 female patients. The mean age at ophthalmological examination was 42.8 years, range 20.5–77.7 years. The mean age at the time of HCU diagnosis was 25.3 years (range 4–68 years). All patients were receiving treatment at their time of inclusion.

Ten patients were B₆ responsive, six patients were partially B₆ responsive, and two patients were B₆ non-responsive. Among the 18 patients, three sibling pairs were identified. The secondarily diagnosed siblings were excluded from the analysis of age at diagnosis and time to diagnosis, leaving 15 patients. Grouped by B₆ responsiveness, with the partially and non-responsive patients in the same group due to the small number of patients, the mean age at HCU diagnosis was 30.9 years (range 15–61 years) in the B₆-responsive group (n = 9), compared to 14.2 years (range 4–27 years) in the non/partially B₆-responsive group (n = 6) (p = 0.017).

Ocular manifestations typical for HCU like severe myopia or ectopia lentis presented prior to HCU diagnosis in 8/18 patients, based on data from medical records. Five of these patients (5/8) presented with severe myopia as the first manifestation of HCU, four of them later developed ectopia lentis. Two patients (2/8) presented with ectopia lentis as first manifestation of HCU. In one patient (1/8), both severe myopia and ectopia lentis presented prior to HCU diagnosis, but then the patient already had suffered from a thrombosis so neither ocular manifestation was the first manifestation of HCU.

Regardless of first presentation or not, six patients had experienced or suffered from ectopia lentis prior to diagnosis. One single patient developed ectopia lentis after HCU-diagnosis. Table 1 and Figure 1.

Figure 1. 1a and 1b Patient with homocystinuria, 60 years of age, with bilateral ectopia lentis (subluxated lenses) and severe myopia.

Table 1. Summary of visual and ocular findings in patients with homocystinuria, including symptoms, ectopia lentis and myopia prior to diagnosis, best-corrected visual acuity, strabismus, refraction, surgery due to ectopia lentis, retinal pathology, and other typical homocystinuria manifestations.

Patient, age#	Eyeglasses	Symptoms	Ectopia lentis prior to diagnosis	Myopia prior to diagnosis	BCVA RE/LE	Strabismus	SE D RE/LE at inclusion	Posterior OCT RE/LE	UWFI RE/LE	Other HCU manifestation	Ectopic lentis (surgery)
B6 responsive:
3. 60y	Yes	No	Yes	Severe	1.0/1.0	No	−7.63/-6.88	N/N	N/N		Subluxated. No
6. 20y	Yes	Dry eyes	No	No	1.3/0.4	Esotropia LE	+2.13/+3.25	N/N	N/N		No
7. 70y	Yes	Light sensitivity	No	No	0.9/1.0	No	+2.25/+2.13	RA/RA	Peripheral RA, PM/peripheral RA, PM		No
8. 80y	Yes	No	Yes	Severe	0.65/0.65	Exophoria	+10.13/+10	N/N	Peripheral RA, PM/Peripheral RA, PM		Bilateral, non-IOL (aphakic)
9. 30y	No	No	No	No	1.0/1.0	Exophoria	+1.38/+0.38	NA/NA	NA/NA	Cavernous sinus thrombosis (14y)	No
12. 50y	Yes	No	Yes	Mild	1.0/Prosthesis	No	NA/Prosthesis	N/Prosthesis	N/Prosthesis	Cavernous sinus thrombosis (20y, 22y, 25y) Secondary glaucoma	Bilateral, non-IOL (aphakic) + prothesis LE *
14. 40y	Yes	Light sensitivity	No	No	1.0/1.0	No	−0.25/-0.25	Mild RA/mild RA	N/N	Cavernous sinus thrombosis (23y)	No
15. 50y	Yes	Dry eyes	No	Mild	1.0/1.0	No	−3.75/-3.88	N/N	N/PM in ascending vessel		No
17. 50y	Yes	No	No	Severe	1.0/1.0	No	−4.75/-5.25	N/N	RA/N	Deep vein thrombosis (20y)	No
18. 60y	Yes	No	No	No	1.0/1.0	No	+2/+1.63	N/N	N/N		No
Partially B6 responsive:
1. 50y	Yes	No	No	Mild	1.0/1.0	Exophoria	−5.87/-6.12	N/N	NA/NA	Cavernous sinus thrombosis (18y)	No
2. 60y	Yes	No	Yes	NA	0.9/0.15	No	NA/NA	N/RA, staphyloma	N/Pronounced peripheral RA and PM		Bilateral, IOL
5. 30y	Yes	No	Yes	Severe	1.0/1.3	Exophoria	NA/NA	N/N	N/N		Bilateral, IOL
11. 30y	Yes	Dry eyes	Yes	Severe	1.0/0.9	Exophoria	NA/NA	N/N	TV RE LE		Bilateral, IOL
13. 30y	Yes	Light sensitivity	No	Mild	0.7/0.7	No	−3.88/-1.88	N/N	N/Peripheral RA		No
16. 30y	Yes	Dry eyes, light sensitivity	Yes	Severe	Prosthesis/0.5	No	Light perception/-5.25	NA due to corneal opacities/N	NA due to corneal opacities/TV, RA		Bilateral, IOL
B6 non-responsive:
4. 30y	Yes	No	No	No	0.4/0.8	No	−6.5/-1.88	N/Mild RA	N/N		No
10. 30y	Yes	No	No	No	0.65**/1.0	Hypertropia	+4.38/+1.25	NA/NA	N/N		No

BCVA, best-corrected visual acuity; RE, right eye; LE, left eye; SE, spherical equivalent; D, diopters; OCT, optical coherence tomography; UWFI, ultra-widefield imaging; HCU, homocystinuria; y, years; N, normal; RA, retinal atrophy; PM, pigmentary mottling; NA, not applicable; IOL, intraocular lens; TV, tortuous retinal vessels. Definition: Myopia, Severe <-6 diopters, Moderate −1.5 to −6 diopters, Mild 0 to −1.5 diopters.

*Due to secondary glaucoma complication.

**anisometropic as child.

#Patient age given as approximation.

3.2. Symptoms and best-corrected visual acuity

Seven patients experienced light sensitivity or dry eyes: six female patients and one male patient. The mean BCVA was 0.99 (range 0.65–1.3 right eye (RE)) and 0.81 (range amaurosis-1.0 left eye (LE)) in the B₆-responsive group and 0.71 (range amaurosis-1.0) RE and 0.79 (range 0.15–1.3) LE in the partially or non B₆-responsive group.

The mean BCVA for the 7/18 patients who were treated for ectopia lentis or had subluxated lenses was 0.79 (range amaurosis-1.0) RE and 0.64 (amaurosis-1.3) LE. Two patients who underwent surgery for ectopia lentis were blind in one eye. Both had suffered from retinal amotio, and repeated retinal surgery had failed. One patient had been enucleated due to severe secondary glaucoma, and the other patient had developed severe corneal opacities with vascular ingrowth Figure 2.

Figure 2. Exterior image from 30-year-old patient displaying dense corneal opacities with growth of vessels in the right eye which was blind after repeated surgery for retinal detachment after ectopia lentis.

Regular use of eyeglasses was reported by 17/18 patients. A total of 7/18 patients, three in the B₆-responsive group and four in the partially or non B₆-responsive group had experienced bilateral lens dislocation. Six of these seven had undergone lens surgery, with four patients receiving intraocular lenses (IOL), while two patients were left aphakic. One patient had only slightly subluxated lenses and did not need surgery. For four of the six patients, lens surgery was performed prior to year 2000, and it is likely that many of their complications could have been avoided with modern surgical techniques Figure 3.

Figure 3. Patient with homocystinuria, 30 years of age, who underwent ocular surgery at 25 years of age because of ectopia lentis, where the crystalline luxated lens was removed and replaced with an intraocular lens (IOL). Several surgical re-operations were needed as the IOL also luxated. Diagnosis of HCU was established three years after the first surgery.

3.3. Ocular coherence tomography (OCT) and ultra-widefield imaging (UWFI)

OCT images and UWF images from both eyes were available for 14 patients and from the one remaining eye in the two patients with monocular prostheses or dense corneal opacities. Pathological findings were present in 4/16 patients examined with OCT: two patients with mild retinal atrophy and two patients with moderate atrophy.

Pathological findings were present in 8/16 patients examined with UWF images, with peripheral atrophy being most common (four patients). A summary of OCT and UWFI findings is shown in Table 1 and Figure 4.

Figure 4. a, b and c OCT- and UWFI-images from a 70-year-old patient with homocystinuria. OCT showing bilateral retinal atrophy. UWFI-images showing bilateral peripheral pigmentary changes and retinal atrophy.

3.4. Duration from onset of ophthalmological manifestations to diagnosis

Only two patients were diagnosed immediately after presenting with ocular manifestations (both ectopia lentis), while three patients were diagnosed due to a diagnosed sibling and 13 patients were diagnosed due to non-ocular manifestations. Among the latter, 5/13 patients were diagnosed due to a thrombotic event (four after sinus cavernous thrombosis and one after deep vein thrombosis), 3/13 patients due to fatigue or depression, 3/13 patients due to a marfanoid habitus, one patient was diagnosed due to an intellectual disability and one patient due to suspected connective tissue disease. The mean delay between presenting with severe myopia or ectopia lentis as the possible first manifestation to an established HCU diagnosis for 7/15 patients (three siblings excluded) was 12.0 years (range 2–25 years). The patients’ mean age at diagnosis was 21.3 years (range 8–30 years).

When grouped by B₆ responsiveness, the longest mean duration (18.7 years, range 12–25 years) from the onset of eye changes to HCU diagnosis was found in the group of B₆-responsive patients (n = 3), while the partially responsive or B₆ non-responsive patients (n = 4) had a mean duration of 7.0 years (range 2–10) to diagnosis.

A summary of the type of ocular manifestation as the first manifestation and duration to diagnosis is presented in Figure 5.

Figure 5. Duration from onset of first ocular manifestation to diagnosis in patients presenting with ocular manifestations, such as ectopia lentis or severe myopia, prior to a diagnosis of homocystinuria. Several patients had both before being diagnosed. Duration from the onset of the first ocular manifestation of homocystinuria to diagnosis is shown in blue. The eye symbol indicates ocular manifestation, and the black box indicates a thrombotic event. “D” indicates time of diagnosis, “EL” indicates ectopia lentis, and “SM” indicates severe myopia.

The mean duration from the onset of a thrombotic event to diagnosis for the five patients in which the events led to HCU diagnosis was 5.6 years (range 1–16 years).

3.5. Quality of life, VFQ-25

VFQ-25 was completed by 14/18 patients, nine patients with B₆-responsive HCU and five patients with partially B₆-responsive HCU. The median composite score for all 14 patients was 93 (range 73–98). The median composite score was 94 (range 73–98) in B₆-responsive patients and 92 (range 75–94) in partially or non B₆-responsive patients. The median composite score was 93 (75–94) in patients who had undergone surgery (n = 5) and 94 (73–98) in patients who had not undergone surgery (n = 9). The lowest scores were observed in the sub-scales “General vision” (median 80, range 40–100) and “Distance activities” (median 87.5, range 42–100) (Table 2).

Table 2. Demographic data, visual and ocular findings, and results of visual quality of life in a group of 18 patients with homocystinuria.

Median age at inclusion (years)	42.8 (range 20.5–77.7)
Sex	7 male, 11 female
B6-responsive	10/18
Refractive Error	17/18
Subjective symptoms (light sensitivity/dry eyes)	7/18
Strabismus	7/18
Ectopia lentis prior to diagnosis	6/18
Severe myopia prior to diagnosis	6/18
Pathologies presented on OCT	4/16
Pathologies presented on UWFI	8/16
Mean BCVA RE/LE	0.86 (range amaurosis-1.3 (RE))/0.8 (range amaourosis-1.3 (LE))
Median VFQ-25 composite score	93, range 73–98, n = 14

OCT, optical coherence tomography; UWFI, ultra-widefield imaging; BCVA, best-corrected visual acuity; RE, right eye; LE, left eye; VFQ-25, Visual Function Questionnaire 25; n, number of patients.

4. Discussion

This clinical cohort study aimed to assess visual functions, ocular manifestations, visual quality of life, and time from eye manifestations to metabolic diagnosis in patients with HCU, grouped by B₆ responsiveness. The main findings were a high prevalence of severe myopia (33%) prior to diagnosis and a high percentage of ectopia lentis (39%) experienced at any time during life. Out of the seven patients who had suffered from ectopia lentis, 6/7 (86%) had undergone surgery, 2/6 patients (4/12 eyes; 33%) were left aphakic, and 2/12 eyes were blind due to retinal detachment where repeated retinal surgery had failed.

Mulvihill et al. (28) reported that all 14 patients (100%) included in their study had ectopia lentis at the time of diagnosis, compared to 33% in our study. They also reported a shorter median duration from onset of eye changes to diagnosis (4.0 years) compared to 10.0 years in the current study. The lower frequency of ectopia lentis in the current study could perhaps be explained by the fact that in the study by Mulvihill et al. all patients were B₆ non-responsive, while only 2/18 patients (11%) were B₆ non-responsive in the current study. These two patients were also the two youngest patients at the time of diagnosis (4 and 5 years of age) and thus received adequate treatment early, probably preventing more severe clinical complications. Supporting this theory is the fact that, when grouped by B₆ responsiveness, the prevalence of ectopia lentis was higher in the partially B₆-responsive group (67%) than in the B₆-responsive group (30%) in our study. Neither of the two patients in the non B₆-responsive group in our study had experienced ectopia lentis.

In a study conducted by Al-Dewik et al. (29), ocular manifestations such as myopia and ectopia lentis at the time of diagnosis were reported in 34/69 (49%) in patients with a median age of 8 years at the time of diagnosis. In the current study, ocular manifestations were present in 44% of the patients at the time of diagnosis, which was even later, at 21.5 years.

To the best of our knowledge, the only previous report to use OCT in patients with HCU is that of Gus et al. (30), in which four patients were examined with OCT. Keratoconus was observed in one patient, lens surgery scars in two patients, and peripheral retinal hyperpigmentation in one patient (30). In the current study, 25% of the patients had pathological retinal findings on posterior OCT images. A total of 38% had normal posterior OCT images whilst displaying pathologies on their UWF images. This finding suggests an advantage of including UWFI in the ophthalmological examinations of HCU patients, to detect peripheral retinal findings. However, no specific conclusions could be drawn regarding the probably age-related pathologies detected by OCT and UWFI in these patients.

The mean duration from the onset of ectopia lentis and/or severe myopia, that is typical eye changes related to HCU to diagnosis, varied, but was 12 years (range 2–25 years) in the whole group, when siblings were excluded. When grouped by B₆ responsiveness, the longest mean duration (18.7 years, range 12–25 years) from the onset of eye changes as the first manifestation to HCU-diagnosis was found in the group of B₆-responsive patients (n = 3), while the partially responsive or B₆ non-responsive patients (n = 4) had a mean duration of 7 years (range 2–10) to diagnosis. A possible explanation could be that the partially B₆-responsive patients tend to present with other more severe manifestations at an earlier stage (2) and are therefore diagnosed earlier than the B₆-responsive patients.

One example of this is the case of one B₆-responsive patient who, despite suffering from bilateral ectopia lentis at age 22 and three cavernous sinus thrombosis, was diagnosed 29 years after the first manifestation (severe myopia). Knowledge about early manifestations of HCU combined with early evaluation of homocystinuria could save the patients from other serious disease manifestations, including sinus thrombosis.

The median composite score for the VFQ-25 questionnaire in the current study was 93 (range 73–98). The results, although high when compared to visual quality of life studies on diseases such as diabetic retinopathy (61 in male patients and 53 in female patients) (31), suggest a slight effect on the visual quality of life in HCU patients. When discussing the VFQ-25 results it is important to remember that the questionnaire was only completed by B₆-responsive patients and partially B₆-responsive patients, not by the B₆ non-responsive patients due to their intellectual disabilities.

To our knowledge, the only previous study to evaluate quality of life in patients with HCU was the one conducted by Al-Dewik et al. (29), where a different questionnaire (PedsQL) was used. Although PedsQL 4.0 has been used in studies of several eye diseases (32), it is designed to measure overall quality of life in patients aged from 2 to 18 years of age, whilst VFQ-25 aims to assess visual-related quality of life in adults. Despite the use of a different questionnaire, Al-Dewik et al. (29) found that quality of life was slightly affected in their patients, with a mean total score of 88% compared to 93% in the current study. Another study by our team, on patients with Fabry disease (33), showed a VFQ-25 median composite score of 94%, similar to the current study.

5. Conclusions

The results of this study showed a high prevalence of severe myopia and ectopia lentis prior to diagnosis in patients with HCU. Despite these typical ocular manifestations, delayed diagnosis of HCU was common, and the delay was more pronounced in the B₆-responsive group. Knowledge about early ocular manifestations of HCU could prevent HCU patients from developing other severe diseases.

Ocular complications resulted in monocular blindness in two patients. A decreased visual quality of life was experienced by patients with HCU. Furthermore, retinal imaging identified additional pathologies; however, they were probably not related to HCU. Whether early diagnosis can reduce severe ocular complications and whether modern surgical techniques have improved visual outcomes following ectopic lens surgery remains to be evaluated.

Authors’ contributions

Conception and design: KTF and MO

Analysis and interpretation of the data: AK, KTF, MO, MN, DE

Drafting of the article: AK, KTF, MO, MN, DE

Revising it critically for intellectual content: KTF and MO

Final approval of the version to be published: KTF, MO, MN, DE, AK

All authors agree to be accountable for all aspects of the work.

Acknowledgments

The authors would like to thank the patients who participated in this study. The VFQ-25 questionnaire used in this study was designed by the National Eye Institute in the US.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this article.

Data availability statement

The data that support the findings of this study are available on request from the corresponding author, KTF. The data are not publicly available due to containing information that could compromise the privacy of research participants.

Additional information

Funding

The author(s) reported that there is no funding associated with the work featured in this article.