Cardiac phenotype in propionic acidemia – Results of an observational monocentric study

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Cardiac phenotype in propionic acidemia – Results of an observational monocentric study A. Kovacevica, S.F. Garbadeb, G.F. Hoffmannb, M. Gorenfloa, S. Kölkerb, C. Staufnerb, a b

⁎

Department of Pediatric and Congenital Cardiology, University Hospital Heidelberg, Heidelberg, Germany Department of General Pediatrics, Division of Neuropediatrics and Metabolic Medicine, University Hospital Heidelberg, Heidelberg, Germany

A R T I C LE I N FO

A B S T R A C T

Keywords: Propionic acidemia PA Cardiomyopathy Acquired long QT syndrome Left ventricular diastolic dysfunction

Background: Propionic acidemia (PA) is an organic aciduria caused by inherited deficiency of propionyl-CoA carboxylase. Left ventricular dysfunction and QT prolongation may lead to life-threatening complications. Systematic analyses of cardiac phenotypes, in particular effects of specific cardiac therapies, are scarce. Methods: In this longitudinal observational monocentric study (data from 1989 to 2017) all PA patients treated at our center were included. Echocardiographic parameters (left ventricular end-diastolic diameter: LVEDD, left ventricular shortening fraction, mitral valve Doppler inflow pattern) and 12‑lead electrocardiogram recordings (corrected QT interval: QTc) were analyzed. Symptomatic patients were dichotomized to the group “early-onset” (symptoms within 28 days of life) and “late-onset” (symptoms after 28 days). Associations between cardiac function, LVEDD, QTc and clinical parameters (age at onset, beta-blocker or Angiotensin-converting enzyme inhibitor = ACE-I therapy) were analyzed. Results: 18 patients with PA were enrolled, 17 of them were symptomatic and one asymptomatic, with a median age at diagnosis of 6 days. 14/17 (82%) had early onset disease manifestation. Systolic left ventricular dysfunction (i.e. hypokinetic phenotype of cardiomyopathy) was diagnosed in 7/18 (39%) patients at a median age of 14.4 years, all had early onset. Two patients had a dilated left ventricle and systolic left ventricular dysfunction (i.e. dilated hypokinetic phenotype – dilated cardiomyopathy). Diastolic left ventricular dysfunction was found in 11/18 (61%) individuals, typically preceding systolic left ventricular dysfunction. ACE-I therapy did not improve systolic left ventricular function. Mean QTc was 445 ms (+/− 18.11 ms). Longer QTc was associated with larger LVEDD. Conclusions: Systolic left ventricular dysfunction was found in 39% of patients, reflecting high disease severity. Two thirds of all individuals showed signs of diastolic left ventricular dysfunction usually preceding systolic left ventricular dysfunction; it therefore may be considered as an indicator for early cardiac disease manifestation, possibly allowing earlier treatment modification. Unresponsiveness to routine cardiac therapy highlights the need to evaluate further strategies, such as liver transplantation.

1. Introduction Propionic acidemia (PA; MIM: 606054) is an organic aciduria caused by inherited deficiency of mitochondrial propionyl-CoA carboxylase [1] [2]. Propionyl-CoA carboxylase catalyzes the conversion of propionyl-CoA to methylmalonyl-CoA, a step shared in the catabolic pathways of L-isoleucine, L-methionine, L-threonine, L-valine, odd-

chain fatty acids and the cholesterol side chain finally resulting in the formation of the anaplerotic metabolite succinyl-CoA, which enters the tricarboxylic acid (TCA) cycle [3]. Propionogenic gut bacteria significantly contribute to the daily propionate load [4]. A defect of this enzyme leads to accumulation of propionyl-CoA and formation of pathological metabolites such as 2-methylcitrate, 3-hydroxypropionate, tiglylglycine, and propionylglycine. Propionyl-CoA and 2-methylcitrate

Abbreviations: ACE-I, angiotensin-converting enzyme inhibitor; aLQTS, acquired long QT syndrome; CM, cardiomyopathy; ECG, electrocardiogram; E-IMD, European registry and network for intoxication type metabolic diseases; EO, early-onset; SF, shortening fraction; LME, linear mixed effect models; LO, late-onset; LV, Left ventricular; LVEDD, left ventricular end-diastolic diameter; PA, Propionic acidemia; QTc, corrected QT interval; SCD, sudden cardiac death; TCA, tricarboxylic acid ⁎ Corresponding author at: Department of General Pediatrics, Division of Neuropediatrics and Metabolic Medicine, University Hospital Heidelberg, Im Neuenheimer Feld 430, 69120 Heidelberg, Germany. E-mail address: [email protected] (C. Staufner). https://doi.org/10.1016/j.ymgme.2020.02.004 Received 8 November 2019; Received in revised form 7 February 2020; Accepted 7 February 2020 1096-7192/ © 2020 Elsevier Inc. All rights reserved.

Please cite this article as: A. Kovacevic, et al., Molecular Genetics and Metabolism, https://doi.org/10.1016/j.ymgme.2020.02.004

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Table 1 Study individuals. ID

sex (m/f)

age at onset of symptoms (days)

age at last visit (years)

number of metabolic decompensations

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

m m m f f f m f f f m m m m m f f m

2 6 4 4 357 7 3 3 11 154 1 6 2 1 7 28 n.a.b 72

6.6 7.9 15.8 11.1 8.2 20.6 6.1 4.6 25.4 10.6 14.9 20.9 22.6 9,9a 19.6 15.5 2.8 0.9

39 26 45 20 7 37 22 21 16 33 94 12 4 12 11 26 0 1

CMP (+)

dilated CMP (+)

+ +

diastolic LV dysfunction (+)

+ + + +

+

+ + + +

+ +

+ + + + + + +

QTc max. (ms.) 447 495 564 470 445 470 450 476 480 430 470 460 430 480 475 400 419 441

beta blocker (+)

ACE-I (+)

+ + +

+ +

+

+

+ + +

Table 1 shows age at onset of symptoms and last visit of included PA patients, absolute number of metabolic decompensations, type of CM, presence of diastolic LV dysfunction, maximum QTc interval and cardiac treatment (beta blocker and/or ACE-I). f: female, m: male. a patient died at the age of 10 years. b asymptomatic.

PA diagnosed between 1989 and 2017 at our center were enrolled in this observational monocentric study (n = 18). Long-term biochemical and clinical follow-up data were obtained from the E-IMD (https:// www.eimd-registry.org/) registry which was approved by the institutional ethic committee (application no. S-525/2010). Written informed consent was obtained for all patients before enrolment. Symptomatic patients were dichotomized to the group “EO” (symptoms within 28 days of life) and “LO” (symptoms after 28 days). Table 1 shows onset types, age at last visit and cardiac parameters of included individuals.

are thought to be the major endogenous toxins of PA, inhibiting pyruvate dehydrogenase complex and multiple enzymatic steps of the TCA cycle causing synergistic bioenergetic impairment [5]. Besides acute life-threatening metabolic decompensation, long-term disease manifestations of PA, even those not suffering from metabolic decompensations for years, include progressive neurological disease, myopathy, pancreatitis, and cardiac pathologies such as cardiomyopathy (CM), acute cardiac dysfunction during metabolic crisis and acquired long QT syndrome (aLQTS) [6] [7,8] [9,10]. The latter is characterized by prolongation of the corrected QT interval (QTc) predisposing these individuals to potentially life-threatening ventricular arrhythmias [11] [12]. Different types of cardiomyopathies have been described in PA patients, mainly dilated CM [11] [13] [9]. Secondary multiple OXPHOS deficiency due to mtDNA depletion or ineffective mitophagy resulting in accumulation of dysmorphic and dysfunctional mitochondria or lack of carnitine are currently discussed as possible mechanisms [12] [14] [15]. Toxic metabolites may also play an important role in the development of aLQTS [16] [17]. Genetic heterogeneity leads to different clinical pictures from the severe early-onset (EO) form manifesting in the neonatal period to attenuated late-onset (LO) forms. Therapeutic strategies include low protein diet with or without additional use of precursor amino acid-free amino acid supplements, Lcarnitine, non-absorbable antibiotics (e.g. metronidazole, colistin), and cardiac medications such as angiotensin-converting enzyme inhibitors (ACE-I) and/or beta-blockers, also in case of QTc prolongation as prophylactic therapy. CM and sudden cardiac death (SCD) are known to be life-threatening complications in PA [12] [18] [19]. There are only few studies on the cardiac phenotypes in PA patients [6] [9], and systematic analyses of effects of specific cardiac therapies are scarce. Therefore, we aimed to investigate correlations between cardiac function, cardiac dimensions, QTc intervals and cardiac therapy in a single center study over a period of almost three decades.

2.2. Analysis of cardiac parameters Echocardiographic parameters (left ventricular end-diastolic diameter: LVEDD, and LVEDD z-scores; shortening fraction in percent of total – SF: to assess systolic LV function; mitral valve Doppler inflow patterns: to assess diastolic LV function) and 12‑lead electrocardiogram (ECG) recordings (QTc according to Bazett's formula) were analyzed [20] [21] [22] [23]. ECG recordings were made with the Electrocardiograph ELI 350, Mortara Instrument Inc., Milwaukee, WI, USA. Examples of ECGs and Echocardiograms are shown in Figs. 1a–c and 2a–c. ECG recordings were taken with a paper speed of 50 mm/s (resting ECGs during routine follow-up visits). QTc intervals were measured manually from lead II (three consecutive cycles were measured to calculate a mean value). The QT interval was defined as the interval between the beginning of the QRS complex and the end of the T wave. Onset and offset of T wave were defined as the intersections of the isoelectric line and the tangent of the maximal slope on the up and down limbs of T wave. QTc intervals were calculated according to Bazett's formula [20]. Care was taken to avoid U waves in any measurement. If U waves were present, the end of T wave was taken as the nadir between T and U waves. At the time of QT evaluation all patients were hemodynamically stable and none had electrolyte disturbances, atrial fibrillation or significant intraventricular conduction defects. We documented any cases with T wave alternans or T wave notching, ventricular arrhythmias, syncope or SCD. Further we analyzed available 24-h Holter ECG recordings. Echocardiograms were made with two ultrasound systems:

2. Material and methods 2.1. Setting and study population The study was conducted in a Tertiary Medical Centre (University Children's Hospital Heidelberg). All patients presenting with confirmed 2

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Fig. 1. a–c (Case 1): PA patient, male, at the age of 9 years: dilated cardiomyopathy, QTc prolongation. a) ECG: Sinus rhythm, heart rate: 96 beats per minute, QRS axis: -50°, wide based and late onset T wave, signs of left ventricular hypertrophy, QTc interval 482 ms QT (Bazett's formula: QTc= RR ). b) Echocardiogram: apical four chamber view: dilated left ventricle (LVEDD 5.4 cm; LVEDD z-score: +2.7). c) Echocardiogram: M-mode, parasternal long axis cut through the LV: shortening fraction SF 17% (reduced systolic LV function). Abbreviations LV: left ventricle, RV: right ventricle, LA: left atrium, RA: right atrium, M-mode: motion mode, LVEDD: left ventricular end-diastolic diameter, PA: propionic acidemia, QTc interval: corrected QT interval, QT: QT interval, RR: RR interval.

preload changes during echocardiograms used for this analysis. None of the patients had mitral valve disease. Both would have affected analysis of E/A ratio. All patients had sinus rhythm and heart rates within normal limits during data acquisition. All echocardiography data were taken from routine follow-up exams.

1. Philips Diagnostic Ultrasound System, iE33, software version 6.0.0.845, Philips Ultrasound, Bothell WA, USA, and 2. General Electric Vingmed Ultrasound System, Vivid 7, Software version 7.3.0. GE Medical Systems, Boston MA, USA. Longitudinal echocardiography data was acquired with Philips Excelera R4.1, a cardiology image management, analysis, and reporting system software (R4.1L1-SP1; Philips Medical Systems Nederland B.V., 2014). According to the generally used definition of cardiomyopathy in children and in line with the literature on CM in PA [9], CM (hypokinetic phenotype) was diagnosed if SF was below 28% (i.e. impairment of LV systolic function), determined by motion-mode (m-mode) echocardiography in a standard parasternal long axis view [24]. Dilated CM (dilated hypokinetic phenotype) was diagnosed if the LVEDD z-score was > 2; LVEDD was measured using m-mode echocardiography (parasternal long axis view) [21]. Mitral valve Doppler (pulsed wave Doppler) inflow patterns (to measure E/A ratio: ratio of the peak velocity inflow across the mitral valve in early diastole = “E wave” and peak velocity inflow across the mitral valve due to atrial contraction in late diastole = “A wave”) were analyzed and compared to age dependent normal values in order to assess diastolic LV function [22] [23]. None of the patients had acute

2.3. Statistical analysis Statistical analysis was performed using R language for computational statistics (R Core Team (2017). R: language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/). Besides descriptive analysis, associations between cardiac function, LVEDD, QTc and clinical parameters (age at onset, beta-blocker or ACE-I therapy) were computed using linear mixed effect models (LME) [25] with Satterthwaite approximations to degrees of freedom [26]. Two groups were compared with paired or unpaired t-tests. The potential effect of metabolic decompensations per patient (defined as hyperammonemic decompensation with NH3 > 100 μmol/L) on the onset of CM were analyzed by Welch t-test; the potential effect of metabolic decompensations per patient on QTc were analyzed by Pearson correlation. Differences between age of onset of CM and age of last visit of 3

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Fig. 2. a–c (Case 2): PA patient, female, at the age of 11 years: normal systolic left ventricular function, subtle QTc prolongation. a) ECG: Sinus rhythm, heart rate: 84 beats per minute, QRS axis: +70°, late onset T wave, QTc interval 451 ms (Bazett's formula: QTc=

QT RR

).

b) Echocardiogram: apical four chamber view: normal sized left ventricle (LVEDD 4.3 cm; LVEDD z-score: +0.13). c) Echocardiogram: M-mode, parasternal long axis cut through the LV: shortening fraction SF 28-29% (normal systolic LV function – lower limit of the normal range). Abbreviations LV: left ventricle, RV: right ventricle, LA: left atrium, RA: right atrium, M-mode: motion mode, LVEDD: left ventricular end-diastolic diameter, PA: propionic acidemia, QTc interval: corrected QT interval, QT: QT interval, RR: RR interval.

were made 6 times per case in median (range 1–18). Mean QTc of all cases was 445 ms (+/− 18.11 ms SDS); however individual range was up to 564 ms. 9/18 patients (50%) had at least one documented QTc of > /= 470 ms. We did not observe ventricular arrhythmias or cardiac events such as SCD in any patient. 12/18 patients had 24-h Holter ECGs, none showed significant ventricular dysrhythmias. Longer QTc is associated with higher LVEDD z-scores in 10 cases as shown in Fig. 3 (β = 4.25; t(79.44) = 2.05; p = .04; random intercept LME). Two patients were treated with propranolol (patients 2, 3) and two with metoprolol (patients 4, 11) due to prolonged QTc. Fig. 4 shows QTc values over time (years) in patients with at least three documented QTc intervals with and without beta blocker treatment. ACE-I therapy with Lisinopril did not improve SF (Fig. 5). SF even decreased significantly despite ACE-I treatment (t(4) = 3.9, p = .016; paired t-test). 11/18 (61%) individuals show pathological patterns of mitral valve inflow (E/A ratio) demonstrating LV diastolic dysfunction with a median age at diagnosis of 12.4 years; among these 11 patients, 4 did not show signs of systolic LV dysfunction. Among those with diastolic and systolic LV dysfunction, diastolic LV dysfunction always occurred earlier (median 375 days) than systolic LV dysfunction (median age at diagnosis of systolic LV dysfunction 14.4 years). The number of

individuals without CM were tested with Mann-Withney U Test. The probability of developing a CM with age was analyzed using KaplanMeier curves.

3. Results Eighteen patients with PA were enrolled, 17 of them were symptomatic and one asymptomatic with a median age at diagnosis of 6 days (range 1–357 days). 14/17 (82%) were classified as EO and 3/17 (18%) LO. Two of the LO patients were diagnosed neonatally and treated before the onset of symptoms (one diagnosed by newborn screening, the other following diagnostic work-up of a high-risk family, i.e. following identification of an index patient; ID 10 and ID 18, see Table 1). During the study period, one patient died at the age of 10 years due to cardiac decompensation during severe pneumonia; this patient had been put on ACE-I due to CM earlier. See Table 1 for an overview of patient information. During follow-up of the study period echocardiography was performed 7 times per case in median (range 1–17). CM was diagnosed by echocardiography in 7/18 (39%) patients at a median age of 14.4 years (range 2.98–19.5 years); all of those were EO patients. In n = 2 patients with dilated LV, dilated CM was diagnosed, while none developed hypertrophic CM. During follow-up of the study period ECGs incl. QTc measurements 4

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Fig. 3. Association of LVEDD z-scores and QTc intervals for cases where at least three QTc intervals have been documented (14/18). Figure shows individual QTc intervals as a function of LVEDD z-scores. LME shows a weak association between QTc intervals and LVEDD z-scores (β = 4.25; t (79.44) = 2.05; p = .04; random intercept LME). Eight of these 10 patients were early onset (EO, indicated by ○), 2 late onset (LO, indicated by +). Gray lines: fitted QTc values from LME model.

According to international guidelines, the first line treatment for pediatric patients with reduced systolic LV function is ACE-I treatment. All patients from our cohort that were treated because of reduced systolic LV function received the ACE-I Lisinopril. However, in our cohort this treatment did not improve SF over time (Fig. 5). Despite treatment SF decreased further, indicating the progressive character of the disease. Cardiac drug treatment should be amended dependent on NYHA stage or Ross score (e.g. adding beta blockers, diuretics, aldosterone antagonists or digitalis [27]); or individually, if clinical signs of heart failure are not present and systolic LV function is decreasing. NYHA classification of PA patients is difficult, as it often cannot be differentiated whether limitation of physical activities is due to heart failure or extracardiac reasons, such as neuromuscular problems, which become increasingly relevant especially in older patients. However, we recommend that drug treatment should be amended dependent on NYHA stage, where possible. Diastolic LV dysfunction is characterized by impaired LV relaxation with increased stiffness of the LV and elevated ventricular filling pressures. We assessed mitral valve inflow patterns to evaluate LV diastolic function and demonstrated signs of diastolic dysfunction in 11 of 18 patients. This is considerably more than the cases showing systolic LV dysfunction (7/18). Furthermore, if both systolic and diastolic LV dysfunction were diagnosed in the same patient, the latter developed considerably earlier. Therefore, assessing diastolic LV function during routine cardiac follow-up may be considered useful in detecting cardiac involvement in PA at an early stage. This finding may lead to timely cardiac treatment modification, i.e. if diastolic LV dysfunction is present with preserved systolic LV function. Adding aldosterone antagonists may be of potential benefit in patients with diastolic LV dysfunction [28] [29] [30].

metabolic decompensations per case had neither a significant effect on the onset of CM nor a significant effect on QTc. This holds true for both the absolute number of decompensations (CM: p = .39; QTc: p = .60) and for number of decompensations corrected for age (CM: p = .60; QTc: p = .85). For this cohort we can demonstrate that the probability of not having a CM decreases with increasing age (Fig. 6). There is no significant difference between the age of CM onset in CM patients and the age at last visit of patients without CM (p = .79). 4. Discussion This monocentric observational study on cardiac involvement of PA patients aims at describing the cardiac phenotype in PA patients, focusing on the long-term effects of cardiac therapy. 4.1. CM in PA: systolic and diastolic LV dysfunction and treatment options Cardiomyopathies are defined as exclusive primary disease of the myocardium (primary cardiomyopathy) compared to myocardial disease as part of a systemic affection (secondary cardiomyopathy) as in patients with PA. LV systolic function as one main component of the ventricular performance describes the ability of the heart to develop force and deform so it can eject blood. The term CM in the context of reduced systolic LV function in PA is commonly used [6] [9] [24] and CM, as in this study, is often defined as LV-SF < 28%.We demonstrate a CM rate of 39% diagnosed by echocardiography according to this definition. Dilated CM (defined as CM combined with a LV diameter above the normal range) was rare in this cohort (n = 2), and there was no case of hypertrophic CM. This is in line with previous data [6]. A study by Romano and colleagues, however, reported dilated CM with a frequency of 23% [9]. 5

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Fig. 4. QTc over time (years) in PA patients with at least three documented QTc intervals. No significant change of QTc over age was observed (β = −0.71, p = 0,34, LME with random intercept) and no significant difference of QTc between onset (βEO = 456, βLO = 433, p = .18, LME with random intercept) was detected. ID with an Asterisk: patient diagnosed with CM. Dark solid lines are fitted QTc values from LME Model. Horizontal gray lines: QTc limits 440–460 ms (vertical lines: dashed = start Propranolol therapy; solid = start Metoprolol therapy).

Coenzyme Q10 has been discussed as potentially effective to improve LV function, since fatal heart failure in an EO patient was associated with coenzyme Q10 deficiency [15], and in a LO patient with CM and markedly decreased myocardial coenzyme Q10 status cardiac function slowly improved after supplementation with this cofactor [31]. However besides these case reports, there is no evidence for a positive effect of coenzyme Q10 on the prevention or therapy of cardiac disease in PA. The cardioprotective potential of liver transplantation for individuals with PA has been discussed over years [32], and has been reenforced following the report of stabilization or even normalization of cardiac dysfunction after liver transplantation [9] [33] [34] [35] [36]. Our finding that routine ACE-I treatment is not effective to improve SF in PA-CM shows the necessity to evaluate further therapeutic options. Liver transplantation may be such a treatment option, as it has been shown to reverse cardiac disease in PA patients. Interestingly, all CM patients were EO PA cases. Among this subgroup 50% had CM, indicating increased disease severity and increased risk of developing life-threatening CM compared to LO patients. All patients (EO and LO) have been treated according to current management guidelines for PA, and we found no correlation between the number of metabolic decompensations and CM or QTc. Further we can demonstrate that the probability of having a CM increases with age, demonstrating a progressive character of cardiac involvement in PA.

Fig. 5. Mean values of LV shortening fraction without, before and after ACE-I treatment. Despite ACE-I treatment a significant decrease of SF was observed (p = .023). Patients with ACE-I treatment: ID 3, 4, 8, 11, 12 and 14 (see Table 1). 6

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CM in PA [44]. Furthermore, serum N-terminal-pro brain natriuretic peptide was not routinely assessed in this retrospective series, which may be helpful as an additional parameter to assess progression of cardiac disease, for monitoring and guiding heart failure therapy. Cardiac catheterization may be considered in selected cases for hemodynamic evaluation. Further, generalizability of the reported results may be limited due to the retrospective design of the study and the number of cases studied. Therefore, we aim to perform a prospective study including more detailed echocardiographic parameters such as tissue Doppler to explore LV systolic and diastolic function. Furthermore, randomization may help to analyze effects of different strategies regarding cardiac therapy in patients with PA and CM. 5. Conclusions We report a 39% CM rate in our cohort, all of those PA patients with EO. Two thirds of all individuals showed signs of diastolic LV dysfunction which usually preceded systolic LV dysfunction; diastolic LV dysfunction may therefore be considered as an indicator of early cardiac disease manifestation in PA, allowing closer monitoring and timely discussion of treatment options. Routine ACE-I therapy did not lead to an improvement of systolic LV function, highlighting the need for improved targeted therapies or early liver transplantation. Due to limited case numbers per center for this rare disease a multicenter approach for a prospective randomized controlled study would be desirable to further assess cardiac complications and effects of therapy on the cardiac phenotype in PA.

Fig. 6. Kaplan-Meier curve of proportion of patients without CM. Marks: censored individuals, dashed line: 95% confidence interval. We can demonstrate that the probability of not having a CM decreases with increasing age.

4.2. Aquired Long QT syndrome (aLQTS) In 2006, Kakavand and colleagues described for the first time the association of aLQTS and PA [37]. Since then more reports followed [6] [19] [38]. Prolongation of QTc intervals is known to be a risk factor for possibly life-threatening ventricular arrhythmias, as in congenital LQTS [39]. In our cohort mean QTc was 445 ms, thus slightly prolonged; however, the individual maximum was up to 564 ms. QTc prolongation displays a risk factor for ventricular arrhythmias, and SCD in PA is reported in literature [12] [18] [19]. A cornerstone of treatment in congenital LQTS and aLQTS, such as in PA patients, is prophylactic beta-blocker therapy aiming to reduce the frequency of cardiac events [39]. In this retrospective analysis the patient histories did not lead to a suspicion of congenital long QT syndrome. Therefore, in view of an obvious reason for acquired QTc prolongation, long QT genes were not assayed. In this cohort, four patients were treated prophylactically with betablockers (two with Propranolol, two with Metoprolol) due to increased QTc intervals. We did not observe ventricular arrhythmias or cardiac events such as SCD. A direct correlation of higher QTc intervals and larger left ventricles was found (but still within the normal range for LVEDD z-scores), affecting mainly EO PA patients. This has not been described before in the context of CM in PA patients, however it is well known in the context of dilated CM of other causes (idiopathic and metabolic – the latter not including PA patients) and may therefore be discussed as a possible further etiological factor contributing to QTc prolongation [40] [41] [42] [16] [17]. It has been shown that in children with dilated CM with increasing QRS duration and/or further QTc prolongation the risk of life-threatening arrhythmias increases [40] [42] [43]. If this is observed in PA patients, early treatment modification should be considered, e.g. adding beta-blockers and parents should be counseled regarding this risk.

Declaration of Competing Interests The authors have no competing interests to declare. Acknowledgements We thank the patients and their families for contributing their data. We acknowledge the project “European registry and network for intoxication type metabolic diseases (E-IMD)”. The E-IMD registry was used for data collection and retrieval. It has received funding by the European Union (E-IMD; EAHC no 2010 12 01; coordinator: Stefan Kölker), in the framework of the Health Programme. After the end of the EU funding period the E-IMD patient registry has been sustained by funding from the Kindness-for-Kids Foundation, Munich, Germany (ENIMD; coordinator: Stefan Kölker), the Kettering Foundation, Dayton, Ohio, USA (RDCRN #5101; site PI: Georg F. Hoffmann), and Dietmar Hopp Foundation, St. Leon-Rot, Germany (NBS2020; coordinator: Georg F. Hoffmann, S. Kölker). References [1] B. Childs, W.L. Nyhan, M. Borden, L. Bard, R.E. Cooke, Idiopathic hyperglycinemia and hyperglycinuria: a new disorder of amino acid metabolism, I Pediatrics 27 (1961) 522–538. [2] Y.E. Hsia, K.J. Scully, L.E. Rosenberg, Defective propionate carboxylation in ketotic hyperglycinaemia, Lancet 1 (1969) 757–758. [3] P. Wongkittichote, N.A. Mew, K.A. Chapman, Propionyl-CoA carboxylase - A review, Mol. Genet. Metab. 122 (2017) 145–152. [4] G.N. Thompson, J.H. Walter, J.L. Bresson, G.C. Ford, S.L. Lyonnet, R.A. Chalmers, J.M. Saudubray, J.V. Leonard, D. Halliday, Sources of propionate in inborn errors of propionate metabolism, Metab. Clin. Exp. 39 (1990) 1133–1137. [5] M.A. Schwab, S.W. Sauer, J.G. Okun, L.G. Nijtmans, R.J. Rodenburg, L.P. van den Heuvel, S. Drose, U. Brandt, G.F. Hoffmann, H. Ter Laak, S. Kölker, J.A. Smeitink, Secondary mitochondrial dysfunction in propionic aciduria: a pathogenic role for endogenous mitochondrial toxins, Biochem. J. 398 (2006) 107–112. [6] D. Baumgartner, S. Scholl-Burgi, J.O. Sass, W. Sperl, U. Schweigmann, J.I. Stein, D. Karall, Prolonged QTc intervals and decreased left ventricular contractility in patients with propionic acidemia, J. Pediatr. 150 (2007) 192–197 197 e191. [7] M.R. Baumgartner, F. Horster, C. Dionisi-Vici, G. Haliloglu, D. Karall, K.A. Chapman, M. Huemer, M. Hochuli, M. Assoun, D. Ballhausen, A. Burlina, B. Fowler, S.C. Grunert, S. Grunewald, T. Honzik, B. Merinero, C. Perez-Cerda,

4.3. Limitations We acknowledge that echocardiography has its limitations in detecting early signs of CM. It has been shown that delayed-enhancement cardiac magnetic imaging may be helpful in detecting early stages of 7

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