Newborn Screening for SMA – Can a Wait-and-See Strategy be Responsibly Justified in Patients With Four SMN2 Copies?

Abstract

Background:

Early treatment after genetic newborn screening (NBS) for SMA significantly improves outcomes in infantile SMA. However, there is no consensus in the SMA treatment community about early treatment initiation in patients with four copies of SMN2.

Objective:

Approach to a responsible treatment strategy for SMA patients with four SMN2 copies detected in newborn screening.

Methods:

Inclusion criteria were a history of SMA diagnosed by NBS, age > 12 months at last examination, and diagnosis of four SMN2 copies at confirmatory diagnosis.

Results:

21 patients with SMA and four SMN2 copies were identified in German screening projects over a three-year period. In three of them, the SMN2 copy number had to be corrected later, and three patients were lost to follow-up. Eight of the fifteen patients who were subject to long-term follow-up underwent presymptomatic therapy between 3 and 36 months of age and had no definite disease symptoms to date. Five of the other seven patients who underwent a strict follow-up strategy, showed clinical or electrophysiological disease onset between 1.5 and 4 years of age. In two of them, complete recovery was not achieved despite immediate initiation of treatment after the onset of the first symptoms.

Conclusion:

A remarkable proportion of patients with four copies of SMN2 develop irreversible symptoms within the first four years of life, if a wait-and-see strategy is followed. These data argue for a proactive approach, i.e., early initiation of treatment in this subgroup of SMA patients.

Keywords

Spinal muscular atrophy outcome newborn screening presymptomatic treatment

ABBREVIATIONS

SMA

(Spinal Muscular Atrophy)

NBS

(Newborn Screening)

CHOP INTEND

(The Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders)

HINE-2

(Hammersmith Infant Neurological Examination –Section 2)

SMN

(Survival Motor Neuron)

CMAP

(Compound Muscle Action Potential)

INTRODUCTION

Spinal muscular atrophy (SMA) is the most common neurodegenerative disease in childhood. In more than 95% of cases, it is caused by a homozygous deletion of exon 7 of the SMN1 gene, which encodes the survival motor neuron (SMN) protein [1 –3]. Critical deficiency of SMN protein results in degeneration of motor neurons in the spinal cord [4]. Survival of SMA patients, lacking a functional SMN1 gene, depends on production of the SMN protein by a second gene called SMN2, which is nearly identical to SMN1. The higher the number of SMN2 copies, the milder the phenotype of SMA [5, 6].

While two or three SMN2 copies in the vast majority result in disease onset in the first months of life [7], data on disease progression are less clear if patients harbour four SMN2 copies. Many patients remain ambulatory in the long term and the onset of the disease is highly variable. However, the correlations between disease severity and the number of SMN2 copies is a relative and not an absolute one. Regarding former data in the literature, it becomes evident that an individual with four SMN2 copies (if determined correctly) still has a chance of almost 10% to develop symptoms in the first year of life [5]. However, natural history data are lacking to a large extent.

It is largely unknown when patients first develop symptoms, and the time lag between subtle onset of the disease and correct diagnosis can be up to years [8]. SMA-specific therapies that can correct SMN deficiency have been available for several years, and given the outcome of neonatal screening projects for SMA to date, there is no doubt about the indication for presymptomatic therapy in patients with two or three SMN2 copies in the neonatal period [9 –12]. However, there is extensive debate within the SMA treating and SMA researching experts as to whether this treatment should be given to patients with four copies of the SMN2 gene. The reason for some hesitancy is the knowledge that some patients do not develop the disease until late adulthood or may not develop it at all.

This manuscript describes the experience with a cohort of children with four copies of SMN2 identified in newborn screening projects in Germany.

PATIENTS AND METHODS

Details about the German NBS pilot projects were previously published [5 , 14]. In all patients with a homozygous deletion of exon 7 of the SMN1 gene in the dry blood test, confirmation of the diagnosis and SMN2 copy number determination were performed by MLPA using a new whole blood sample in a human genetics laboratory. The methodology of SMN2 copy number determination was changed from the original MLPA kit SALSA MPLA probe mix P021-A2 SMA, MRC Holland to a modernized version (SALSA MPLA probe mix P021-B1 SMA) in February 2019. After one patient was found to have an incorrect quantification of SMN2 copy number, all samples were re-analyzed with the newer kit in two independent laboratories. In addition, one of the treatment centers (University of Münster) recently performs digital droplet PCR from the same blood sample as a second method in all screening patients.

Inclusion criteria were SMA detection by NBS, four copies of the SMN2 gene in the first confirmatory diagnosis, and a minimum age of 12 months at last examination. The data cut-off was February 2022, and the follow-up period of patients ranged from 12 months to 4 years of age. Data collection was performed as part of a prospective cohort study [13]. The local ethics committee of the participating universities (Project No. 18–269) approved the study.

The treatment recommendation was based on the American SMA NBS Multidisciplinary Working Group recommendations, published in 2018 [14], which initially recommended a “watchful waiting” strategy for children diagnosed with SMA and≥4 SMN2 copies. In 2020, the recommendations changed to presymptomatic therapy even in SMA with four SMN2 copies [15], although no clear suggestion was made for age at initiation of therapy. From this point, the recommendation for presymptomatic treatment was communicated to all previously diagnosed patient families and discussed with all newly diagnosed patient families directly at diagnosis. Clinical follow-up included a neurological examination, measurement of ulnar nerve CMAP amplitude, and a standardized physical therapy examination including the CHOP INTEND and the Hammersmith Infant Neurological Examination Section 2 (HINE-2) as previously published [16]. Depending on the patients’ motor skills, endurance, and understanding of the tasks, the Gross Motor Scale of the Bayley Scales of Infant and Toddler Development [17] or the HFSME was performed at 12–40 months of age.

RESULTS

Incidence and correctness of copy number determination

Some of these data have been published in previous reports on the results of SMA-NBS Projects [9, 18 19], but given their relevance to this manuscript, they are summarized again here.

In German screening projects, a total of 62 patients with SMA were identified between January 2018 and January 2021, corresponding to an incidence of approximately 1:7500, which is in the range of the known incidence in Germany [20]. In 21 of them, the first MLPA confirmatory diagnosis revealed four SMN2 copies. Initially, SMN2 copy number was determined by only one genetic laboratory. After the onset of disease in an 8-month-old girl with only three SMN2 copies, which was misdiagnosed to have four copies, reanalysis of copy number by a second laboratory was initiated. In two children, copy number redetermination then revealed five SMN2 copies instead of four. After the change of MLPA kit in 2019, copy number determinations were identical between laboratories in all patients, as was the case with droplet PCRs.

Follow-up period and patients lost to follow-up

Twenty-one children born between January 2018 and January 2021 were enrolled in this study, 18 of whom had a confirmed diagnosis of four SMN2 copies at rediagnosis. Of these 18 patients, three were lost to follow-up between 2018 and 2019 (all before the treatment recommendation for patients with four SMN2 copies was amended in 2020). Long-term follow-up is available for 15 patients.

Early motor development and motor milestone acquisition

All 15 children learned to sit independently, walk with assistance, and walk unassisted within the time periods classified as physiological by WHO. CHOP-INTEND and HINE-2 scores remained entirely within the normal corridor. Swallowing and sucking were normal in all patients at initial presentation and remained so throughout the follow-up period. No cases with respiratory involvement occurred. Ulnar CMAP values were normal in all patients at initial presentation and showed no relevant decrease at follow-up.

Treatment decision and signs of disease in untreated children

In eight of 15 patients, presymptomatic therapy was started at 3–36 months of age with the intention of preventing the onset of the disease. The decision to start therapy was always made together by the physician and family, but there were differences in the families’ basic attitude towards long-term therapy, and some hesitating families found it easier to decide to start treatment when the oral splicing modifier risdiplam became available. Among these eight families were three families with a positive family history. All eight patients, regardless of when treatment was started and what type of therapy was used (Table 1), have shown no symptoms of the disease to date.

Table 1

Patient’s history, clinical and electrophysiological data

Pat. Nr.	SMN2-copy number in re-analysis	Family history	Age at last exam	Motor detori-ation	Electro-physiologic signs of disease	Nusi-nersen from age	Risdi-plam from age	Reason for treatment start	Reason not to treat	Motor Bayley at last exam (age scales)	HFSME at last exam	Ulnar CMAP at last exam (mV)
3	4	Neg	8 mo	?	?	–	–	–	Lost to follow-up	?	?	6,1
7	4	Neg	44 mo	4 y falls	EMG neurogenic age 3y 9 mo	–	4 y	EMG, falls	–	13	66/66	8,5
8	4	Neg	13 mo	?	?	–	–	–	Lost to follow-up	?	?	7,4
9	5	Neg	38 mo	No	Not on NCS; EMG not performed	–	–	–	5 SMN2 copies	11	63/66	10
11	3	Neg	44 mo	8 mo proximal weakness	EMG neurogenic	9 mo	–	Motor detoriation	–	5	51/66	5,1
12	5	Neg	27 mo	No	Not on NCS; EMG not performed	–	–	–	5 SMN2 copies	13	n.a.	6,3
13	4	Pos^*	28 mo	No	Not on NCS; EMG not performed	No	3 y	Presymp-tomatic	–	–	64/66	6,6
14	4	Neg	37 mo	24 mo falls and fatigue	EMG neurogenic age 25 mo	2y 2 mo	–	EMG, falls	–	4	54/66	9,8
23	4	Neg	1 mo	?	?	–	–	–	Lost to follow-up	?	?	?
26	4	Neg	33 mo	no	Not on NCS; EMG not performed	20 mo	2,5 y	Presymp-tomatic	–	10	–	6,6
27	4	Neg	16 mo	No	Not on NCS; EMG not performed	16 mo	–	Presymp-tomatic	–	10	–	5,7
28	4	Pos ^**	33 mo	23 mo falls and insecurity	Not on NCS; EMG not performed	23 months	No	Falls and motor insecurity	–	–	54/66	9,1
30	4	Pos ^***	30 mo	No	Not on NCS; EMG not performed	6 mo	–	presymp-tomatic	–	5 (bad coope-ration)	–	8,6
36	4	Pos^*	21 mo	No	Not on NCS; EMG not performed	9 mo	2y, 2mo	Presymp-tomatic	–	9	–	6,9
37	4	Neg	14 mo	No	Not on NCS; EMG not performed	No	No	–	No symp-toms so far	–	–	7,3
39	4	Neg	12 mo	No	EMG neurogenic age 18 months	–	18 mo	EMG	–	6	–	4,5
40	4	Neg	28 mo	20 mo proximal weakness	Not on NCS; EMG not performed	–	22 m	Motor detoriation	–	–	–	n.a.
48	4	Neg	14 mo	No	No	–	–	–	No symp-toms so far	13	–	4,7
54	4	Neg	16 mo	No	n.a.	3 mo	–	Presymp-tomatic	–	–	–	n.a.
56	4	Neg	18 mo	No	Not on NCS; EMG not performed	4 mo	–	Presymp-tomatic	–	–	–	8,9
60	4	Neg	12 mo	No	No	–	12 mo	Presymp-tomatic	–	10	–	7,1

Pos = positive; neg = negative, y = years, mo = months ^*misdiagnosed brother; ^**maternal uncle deceased with type1 SMA, paternal uncles have type 3 SMA; ^***maternal aunt with type 3 SMA

One of the untreated patients developed proximal weakness at 20 months of age, despite completely unremarkable clinical findings (without EMG examinations) until 19 months of age. Symptoms were not reversible after initiation of therapy at 22 months of age. The child showed signs of SMA type 3 with Trendelenburg gait and Gowers maneuver when standing up. Three untreated children showed mild motor symptoms (two at two and one at three years of age, respectively) with decreased endurance and tendency to fall; disease onset was confirmed by neurogenic EMG in two of them (no EMG was available in the third child), and therapy was initiated promptly in all three. In the oldest patient, the mild proximal weakness did not recover even 9 months after the start of treatment; she supports herself on her thigh when standing up. In the third patient, the initial symptoms also persisted in terms of motor unsteadiness and mild problems with stair climbing. The observation period of the second patient after therapy is too short to assess the outcome. One child under wait-and-see strategy showed initial neurogenic changes without motor correlate on EMG examination at 1.5 years of age, and treatment was initiated. In none of the children did standardized physiotherapy tests or neurography reveal suspicious findings before the onset of symptoms. The presence of deep tendon reflexes did not change in any of the symptomatic children. The two children with five SMN2 copies remained clinically and electrophysiologically unremarkable to date. It was discussed with the parents that a wait-and-see strategy was appropriate. The misdiagnosed child with three SMN2 copies, severe disease onset at eight months of age and treatment initiation at ten months of age, developed an SMA type 3 phenotype with Trendelenburg gait, inability to run, and relevant proximal weakness on getting up.

DISCUSSION

We present data from 21 children identified by NBS between January 2018 and January 2021 with a diagnosis of SMA and four SMN2 copies. In 18 of them, the number of four copies was confirmed in the re-analysis, representing 30% of the total cohort of SMA patients diagnosed by German screening projects to date. In three patients, quantification of SMN2 copy number was incorrect. Fortunately, the commercially available kit was changed in 2019. Nevertheless, MLPA is a semiquantitative method. Although the focus in this manuscript is on the four SMN2 copy number patients, we report on all 21 because despite an improved kit, SMN2 copy number can be misestimated. Accordingly, one patient who had three SMN2 copies did not initially receive appropriate therapy, as we previously reported [9]. In addition, there were two children with correction from four to five SMN2 copies who did not require therapy according to current recommendations and who might have received therapy that was not indicated if no reanalysis of SMN2 copy number had been performed.

SMN-targeted medication has been available to treat SMA since 2017 and although, there is no longer any debate that patients with expected infantile forms must be treated presymptomatically [10 –12], treatment modalities are still highly debatable for patients with four SMN2 copies due to lack of natural history data. There are initial recommendations for the treatment of patients with four copies from other studies. For example, the Canadian group proposed a wait-and-see strategy with 3 months of clinical and electrophysiological monitoring [21]. However, the clinical results from this approach are not yet available.

Our group opted for a more proactive approach after the change in the 2020 recommendations, and this study cohort of patients in whom the four SMN2 copies were actually confirmed was therefore treated inhomogeneously. The change of treatment strategy in the middle of the pilot resulted in a kind of “relative” treatment indication, especially for the patients born in the first two years of the projects.

We report on a group of eight presymptomatic patients and a group of seven children in whom treatment was initiated due to SMA symptoms or who have not been treated at all so far.

The first group has fortunately been without signs of disease to date, although the age at initiation of therapy has varied. A much longer observation period will be required to determine any differences in outcome.

However, the data on the second group show a high number (5 out of 7) of patients who (under close monitoring from diagnosis) showed disease onset between 1.5 and 4 years of age. This proportion is so much higher than expected that a further wait-and-see strategy seems irresponsible for this group of patients. Since the incidence of the pilot projects was in the range of the known German SMA incidence, it must be assumed that no relevant number of patients was identified who will not develop symptoms (which was one of the arguments for a wait-and-see strategy).

Children with four copies of SMN2 have the most favorable genetic conditions for a long-term favorable course under therapy. Although biomarker approaches for disease severity and progression with therapy have been increasingly explored in recent years, there is no established biochemical parameter that predicts onset and disease in patients with late-onset forms of SMA [12 , 22–24]. The knowledge about irreversibility of motor neuron damage and significantly higher SMN levels in early life further support this approach [1, 25].

It seems possible that the regional distribution of patients with four SMN2 copies is different. In the Australian NBS pilot [26], apparently only one of 21 SMA patients was identified with four SMN2 copies, which may be partly due to the small number of cases, but is quite considerably lower than the proportion of patients in the German pilot. There is, of course, the question of the financial burden on the health care system if patients with four SMN2 copies are consistently treated. There are different approaches to calculate the costs of treatments compared to the benefits. It is well established that SMA causes high socioeconomic impact in terms of health and social costs and that the quality of life of affected children is extremely impaired [27 –29] although the milder forms in isolation have never been calculated before. However, common sense suggests that outpatients do not account for the largest proportion of health care costs for symptomatic SMA. Nevertheless, it does not seem at all ethically justifiable to cause permanent disability, regardless of severity, by delaying therapy. If this were accepted, the reporting of patients with four SMN2 copies after newborn screening would have to be questioned by itself. However, the data from this study, in combination with known data from the literature showing that the median latency between symptom onset and correct diagnosis in type 3 patients can be up to years, clearly argue against this approach [8].

CONCLUSION AND RECOMMENDATION

According to these data, the treatment algorithm for SMA and the diagnosis of four SMN2 copies should include a second copy number determination in a second laboratory or by a second method. If the decision is made against SMN-targeted therapy, close monitoring is required. EMG allows early diagnosis but is not available in all centers. Deep tendon reflexes and CMAPs may not be a reliable parameter for detecting disease onset, especially in the early stages of the disease. A very high number of untreated children in this cohort became symptomatic within the first four years of life (5/7), which in at least two cases had irreversible consequences despite initiation of therapy within two months. This results in our clear recommendation for a strictly presymptomatic initiation of therapy in this patient cohort. The best age for initiation of treatment remains unclear; we can only state that we did not observe any cases before the age of 1.5 years. It seems worth mentioning that no family has dropped out of follow-up since we started offering presymptomatic therapy to all families. Regarding the five SMN2 copies, we are managing two children who are now almost four years old and have no symptoms. These families were not recommended to start treatment in their children.

In summary, for patients with four SMN2 copies, we strongly recommend a treatment regimen that includes confirming SMN2 copy number in a second laboratory or with another analytical technique and encouraging parents to start treatment early in childhood. If families nevertheless opt for a wait-and-see strategy, follow-up should be performed with extreme care and, if possible, using EMG monitoring.

LIMITATIONS

This is a descriptive study in which the limited number of patients prevents a more in-depth statistical analysis, or renders such an analysis meaningless.

DECLARATIONS

Ethics approval and consent to participate

The local ethics committees of the participating universities (Ludwig-Maximilians-University of Munich, University of Munster and University of Essen, project no. 18–269) have approved the study. Compliance with guidelines on human experimentation was assured.

CONSENT FOR PUBLICATION

Informed consent for prospective follow-up and publication was obtained from the participating families.

AVAILABILITY OF DATA AND MATERIALS

Detailed data from clinical and electrophysiology studies are available from the corresponding author’s institution in Munich, Dr. v. Haunersches Kinderspital, LMU, Lindwurmstr. 4, 80337 München, Germany, upon reasonable request.

DISCLOSURES

All authors have indicated that they do not have any non-financial conflicts of interest.

FINANCIAL DISCLOSURE

Astrid Blaschek recieved speakers honoraria from Roche, Avexis, Sanofi genzyme outside the submitted work and received consultant fee for advisory board tasks from Novartis.

Dieter Gläser was the co-owner of a commercial entity (Genetikum®, Wegenerstr. 15, 89231 Neu-Ulm, Germany).

Katharina Vill has received travel expenses and speaker fees from Biogen, Novartis and Santhera.

Oliver Schwartz has served as a member of a scientific advisory board for Avexis and received travel expenses and speaker fees from Biogen.

Heike Kölbel has served as a member of a scientific advisory board for Avexis and received travel expenses and speaker fees from Biogen and Sanofi-Aventis.

Ulrika Schara has served as a member of a scientific advisory board and data safety monitoring board for Biogen, Avexis and Novartis and received speaker fees from Biogen, Avexis, PTC and Sanofi-Aventis.

Wolfgang Müller-Felber has served as a scientific advisory board member for Biogen, Avexis, PTC, Sarepta, Sanofi-Aventis, Roche and Cytokinetics and received travel expenses and speaker fees from Biogen, Avexis, PTC, Roche, Sarepta and Sanofi-Aventis.

Cornelia Köhler Cornelia Köhler recieved speakers honoraria from Roche, Novartis, PTC outside the submitted work.

Iris Hannibal and Katja Eggermann have nothing to disclose.

FUNDING SOURCES

Not applicable.

AUTHOR’S CONTRIBUTION

Astrid Blaschek conceptualized and designed the clinical study, collected clinical and electrophyisological data and co-drafted the manuscript.

Oliver Schwartz, Heike Kölbel, Cornelia Köhler, Iris Hannibal and Ulrike Schara collected clinical and electrophyisological data and reviewed the manuscript.

Dieter Gläser performed the genetic confirmation and the SMN2 copy number determination and reviewed the manuscript.

Katja Eggermann performed the genetic SMN2 copy number confirmation and reviewed the manuscript.

Wolfgang Müller-Felber conceptualized and designed the clinical study, collected clinical and electrophyisological data, and reviewed and revised the manuscript.

Katharina Vill conceptualized and designed the clinical study, collected clinical and electrophyisological data, co-drafted the initial manuscript, and reviewed and revised the manuscript.

All authors approved the final manuscript as submitted and agreed to be accountable for all aspects of the work.

Footnotes

ACKNOWLEDGMENTS

The authors thank all the parents of the infants who participated in this study; they also thank the physiotherapist’s Barbara Andres, Stefan Grziwa, Karin Hoffmann, Maren Nitzsche, Elisabeth Rothenfußer, Birgit Warken, and Therese Well who carried out the CHOP INTEND Scores, and the Cystinosis Foundation for its initial support.

The Cystinosis Foundation initiated, designed, and conducted the pilot project for genetic newborn screening for SMA and cystinosis in Germany in 2017. Within this pilot project (in the period from January 2018 to May 2019) 200,901 newborns were tested and a total of 29 newborns with a homozygous deletion in the SMN1 gene were identified []. The Cystinosis Foundation had no impact on the interpretation and publication of the clinical data.

CONFLICTS OF INTEREST

The authors have no conflicts of interest to report.

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