Molecular based newborn screening in Germany: Follow-up for cystinosis

Cystinosis

Cystinosis is a very rare autosomal recessive lysosomal storage disorder with an incidence of 1 : 150,000 - 1 : 200,000, and is caused by mutations in the CTNS gene encoding the lysosomal membrane protein cystinosin, which transports cystine out of the lysosome into the cytoplasm. As a result, accumulation of cystine occurs in almost all cells and tissues, especially in the kidneys, leading to multiple organ involvement. Introduction of drug therapy with cysteamine in the mid 1980s, along with the availability of renal replacement therapy in childhood, have dramatically improved patient outcome. Whereas patients used to die without therapy with end-stage renal failure during the first decade of life, nowadays most patients live well into adulthood without renal replacement therapy, and several reach 40 years. There is robust evidence that early initiation and sustained lifelong therapy with cysteamine are both essential for morbidity and mortality. The rarity of the disease and the multi-organ involvement present an enormous challenge for those affected and the providers of care for this patient group.

Spectral domain optical coherence tomography-based retinochoroidal cystine crystal score: a window into infantile nephropathic cystinosis

PRÉCIS: Cystinosis is a lysosomal storage disease leading to an accumulation of cystine crystals in several organs. We aim to comprehensively describe chorioretinal cystine crystals via spectral domain optical coherence tomography (SD-OCT) and elaborate a new biomarker for systemic disease control.

BACKGROUND/AIMS

Cystinosis is a rare lysosomal storage disease leading to an accumulation of cystine crystals in several organs. This study aims to describe the deposition of retinochoroidal crystals in infantile nephropathic cystinosis and to elucidate their potential value as an objective biomarker for systemic disease control.

METHODS

This cross-sectional study was carried out by the University Eye Hospital of the Ludwig-Maximilian University (Munich, Germany) in collaboration with the German Cystinosis Study Group. A complete ophthalmologic examination was performed, along with posterior segment SD-OCT (Spectralis; Heidelberg Engineering GmbH, Heidelberg, Germany). Retinochoroidal crystals were graded by employing a novel semiquantitative grading system-the retinochoroidal cystine crystal score (RCCCS). To quantify quality of vision, patients completed a specific questionnaire. A total of 85 eyes of 43 patients with cystinosis were included (mean age 22.3±8.8 years, range 6-39; male:female ratio=23:20).

RESULTS

Cystine crystals were detectable in all neuroretinal layers and the choroid, most frequently in the choriocapillaris. The RCCCS was negatively correlated with cysteamine intake (r=0.533, p=0.001) and positively with cystatin C, a stable parameter of renal function (r=0.496, p=0.016). Moreover, the value of the RCCCS affected subjective quality of vision. Genetic analysis indicated pronounced crystal deposition in patients with heterozygous mutations containing the 57-kb-deletion allele of the CTNS gene.

CONCLUSION

Ocular cystinosis leads to retinochoroidal crystal accumulation in every stage of the disease. Crystal deposition may be markedly influenced by oral cysteamine therapy. Therefore, the presented SD-OCT based grading system might serve as an objective biomarker for systemic disease control.

Newbornscreening SMA - From Pilot Project to Nationwide Screening in Germany

Now that targeted therapies for spinal muscular atrophy are available, attempts are being made worldwide to include screening for spinal muscular atrophy in general newborn screening. In Germany, after pilot projects from 2018-2021, it was included in the general newborn screening from October 2021. To ensure a smooth transition, criteria for follow-up were developed together with key stakeholders. At the beginning of the transition to nationwide screening, false positive findings were reported in 3 patients. After optimization of the screening method in the laboratories concerned, all findings have been subsequently confirmed. On average, the first presentation to a neuromuscular center occurred on day 12 of life, and in patients with 2 or 3 SMN2 copies, therapy started on day 26 of life. Compared with the pilot project, there was no significant delay in timing.

Outcome of infantile nephropathic cystinosis depends on early intervention, not genotype: A multicenter sibling cohort study

Infantile nephropathic cystinosis (INC) is an inheritable lysosomal storage disorder characterized by lysosomal cystine accumulation, progressive kidney disease, and multiple extrarenal complications (ERCs). Cysteamine postpones the onset of end-stage kidney disease (ESKD) and reduces the incidence of ERCs; however, cysteamine is generally initiated upon establishment of the renal Fanconi syndrome (FS) and partial loss of kidney function, whereas data on long-term effects of cysteamine administered from neonatal age are lacking. An international multicenter retrospective cohort study of siblings with INC was set up to investigate the outcome in relation to age at initiation of cysteamine versus CTNS genotype, with attention to patients treated with cysteamine from neonatal age. None of the siblings treated from neonatal age (n = 9; age 10 ± 6 years) had reached ESKD, while 22% of their index counterparts (n = 9; age 14 ± 5 years) had commenced renal replacement therapy. Siblings treated with cysteamine from the onset of symptoms at a younger age compared with their index counterparts, reached ESKD at a significant older age (13 ± 3 vs. 10 ± 3 years, p = 0.002). In contrast, no significant difference in ERCs was observed between sibling and index patients, independently from the age at initiation of cysteamine. The CTNS genotype had no impact on the overall outcome in this cohort. In INC, presymptomatic treatment with cysteamine results in a better renal outcome in comparison to treatment initiated from the onset of symptoms. This justifies including cystinosis into newborn screening programs. SYNOPSIS: In infantile nephropathic cystinosis, presymptomatic treatment with cysteamine improves the renal outcome which justifies the inclusion of cystinosis into newborn screening programs.

Parental Burden and Quality of Life in 5q-SMA Diagnosed by Newborn Screening

The aim of this study was to assess the psychosocial burden in parents of children with spinal muscular atrophy (SMA), detected by newborn screening (NBS), for which first pilot projects started in January 2018 in Germany. The survey, performed 1-2 years after children's diagnosis of SMA via NBS, included 3 parent-related questionnaires to evaluate the psychosocial burden, quality of life (QoL)/satisfaction and work productivity and activity impairment in the families. 42/44 families, detected between January 2018 and February 2020, could be investigated. Interestingly, statistical analysis revealed a significant difference between families with children that received SMN-targeted therapy vs. children with a wait-and-see strategy as to social burden (p = 0.016) and personal strain/worries about the future (p = 0.02). However, the evaluation of QoL showed no significant differences between treated vs. untreated children. Fathers of treated children felt more negative impact regarding their productivities at work (p = 0.005) and more negative effects on daily activities (p = 0.022) than fathers of untreated children. Thus, NBS in SMA has a psychosocial impact on families, not only in terms of diagnosis but especially in terms of treatment, and triggers concerns about the future, emphasizing the need for comprehensive multidisciplinary care. Understanding the parents' perspective allows genetic counselors and NBS programs to proactively develop a care plan for parents during the challenging time of uncertainty, anxiety, frustration, and fear of the unknown.

Beneficial effects of starting oral cysteamine treatment in the first 2 months of life on glomerular and tubular kidney function in infantile nephropathic cystinosis

Nephropathic cystinosis is a rare lysosomal storage disease whose basic defect, impaired transport of cystine out of lysosomes, results in intracellular cystine storage. Affected individuals exhibit renal Fanconi Syndrome in infancy, end-stage kidney disease at approximately 10 years of age, and many other systemic complications. Oral cysteamine therapy mitigates the detrimental effects on glomerular function and prevents most of the late complications of the disease but has not shown benefit with respect to the early tubular damage of cystinosis. This is because cystinosis is generally diagnosed in the second year of life, after the damage to kidney tubular function has already occurred. We longitudinally evaluated 6 infants diagnosed and treated with cysteamine from before 2 months of age. The 4 infants with good compliance with cysteamine and consistently low leucocyte cystine levels maintained normal eGFR values, exhibited only minor degrees of renal Fanconi Syndrome, and maintained normal serum levels of potassium, bicarbonate, phosphate, and calcium without electrolyte or mineral supplementation through 2, 4, 10 and 16 years of age. Thus, renal Fanconi syndrome can be attenuated by early administration of cysteamine and renew the call for molecular-based newborn screening for cystinosis.

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

Background: Early treatment after genetic newborn screening 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.

Biomarkers in Nephropathic Cystinosis: Current and Future Perspectives

Early diagnosis and effective therapy are essential for improving the overall prognosis and quality of life of patients with nephropathic cystinosis. The severity of kidney dysfunction and the multi-organ involvement as a consequence of the increased intracellular concentration of cystine highlight the necessity of accurate monitoring of intracellular cystine to guarantee effective treatment of the disease. Cystine depletion is the only available treatment, which should begin immediately after diagnosis, and not discontinued, to significantly slow progression of renal and extra-renal organ damage. This review aims to discuss the importance of the close monitoring of intracellular cystine concentration to optimize cystine depletion therapy. In addition, the role of new biomarkers in the management of the disease, from timely diagnosis to implementing treatment during follow-up, is overviewed.

Patients With Infantile Nephropathic Cystinosis in Germany and Austria: A Retrospective Cohort Study

Background

Infantile nephropathic cystinosis (INC) is a rare lysosomal storage disorder resulting in progressive chronic kidney disease (CKD) and a variety of extrarenal manifestations. This orphan disease remains a challenge for patients, their families and health care providers. There is currently no comprehensive study on patients' clinical course in Germany and Austria.

Methods

A retrospective cohort study including 74 patients at eleven centers of care was conducted. Data on time of diagnosis, CKD stage, leukocyte cystine levels (LCL), extrarenal manifestations, and treatment was collected from medical charts and subsequently analyzed using explorative statistics. Age at initiation of kidney replacement therapy (KRT) was evaluated by Kaplan-Meier analyses for different groups of patients.

Results

Patients were diagnosed at a median age of 15 months (IQR: 10-29, range: 0-110), more recent year of birth was not associated with earlier diagnosis. Oral cystine-depleting therapy (i.e., cysteamine) was prescribed at a median dose of 1.26 g/m² per day (IQR: 1.03-1.48, range: 0.22-1.99). 69.2% of all 198 LCL measurements of 67 patients were within the desired target range (≤ 1 nmol cystine/mg protein). Median time-averaged LCLs per patient (n = 65) amounted to 0.57 nmol cystine/mg protein (IQR: 0.33-0.98, range: 0.07-3.13) when considering only values at least 1 year after initiation of therapy. The overall median height of 242 measurements of 68 patients was at the 7^th percentile (IQR: 1-25, range: 1-99). 40.5% of the values were ≤ the 3^rd percentile. Patient sex and year of birth were not associated with age at initiation of KRT, but patients diagnosed before the age of 18 months required KRT significantly later than those patients diagnosed at the age of ≥ 18 months (p = 0.033): median renal survival was 21 years (95% CI: 16, -) vs. 13 years (95% CI, 10, -), respectively.

Conclusion

Early diagnosis and initiation of cystine depleting therapy is important for renal survival in children with INC. Cysteamine doses and LCL showed that treatment in this cohort met international standards although there is great interindividual variety. Patient growth and other aspects of the disease should be managed more effectively in the future.

Spinal Muscular Atrophy –Is Newborn Screening Too Late for Children with Two SMN2 Copies?

Background: Prompt treatment after genetic NBS for SMA substantially improves outcome in infantile SMA. However, deficiency of SMN-protein can cause damage of motor neurons even prior to birth. Objective: To describe the neurological status at the time of NBS and the reversibility of neurological deficits in a cohort of patients with only two copies of the SMN2 gene. Methods: We present motor, respiratory, and bulbar outcomes of 21 SMA patients identified in newborn screening projects in Germany. Inclusion criteria was initiation of SMN targeted medication at less than 6 weeks of age and a minimum age of 9 months at last examination. Results: Twelve patients (57%) developed completely normally, reaching motor milestones in time and having no bulbar or respiratory problems. Three children (14.5%) caught up after initial delay in motor development. Six patients (29%) developed proximal weakness despite early treatment: Three of them (14.5%) achieved the ability to walk with assistance and the other three (14.5%) showed an SMA type 2 phenotype at the age of 16–30 months. One patient (4.8%) had respiratory problems. Three children (14.5%) had mild chewing problems and two individuals (9.5%) needed feeding via gastrotube. Initial CHOP-INTEND values below 30 could be indicative of a less favourable outcome, whereas values above 50 could indicate a good outcome, however in-depth statistic due to the small case number is not predictive. Conclusion: More than 70% of SMA patients with two SMN2 copies can achieve independent ambulation with immediate initiation of therapy. However, caregivers and paediatricians must be informed about the possibility of less favourable outcomes when discussing therapeutic strategies.

Newborn Screening: Review of its Impact for Cystinosis

Newborn screening (NBS) programmes are considered to be one of the most successful secondary prevention measures in childhood to prevent or reduce morbidity and/or mortality via early disease identification and subsequent initiation of therapy. However, while many rare diseases can now be detected at an early stage using appropriate diagnostics, the introduction of a new target disease requires a detailed analysis of the entire screening process, including a robust scientific background, analytics, information technology, and logistics. In addition, ethics, financing, and the required medical measures need to be considered to allow the benefits of screening to be evaluated at a higher level than its potential harm. Infantile nephropathic cystinosis (INC) is a very rare lysosomal metabolic disorder. With the introduction of cysteamine therapy in the early 1980s and the possibility of renal replacement therapy in infancy, patients with cystinosis can now reach adulthood. Early diagnosis of cystinosis remains important as this enables initiation of cysteamine at the earliest opportunity to support renal and patient survival. Using molecular technologies, the feasibility of screening for cystinosis has been demonstrated in a pilot project. This review aims to provide insight into NBS and discuss its importance for nephropathic cystinosis using molecular technologies.

The Editor's Choice for Issue 3, Volume 7

Dear Readers: Choosing one paper from a total of 28 papers published in the third issue of Volume 7 was quite a challenge [...].

Molecular Mechanisms and Treatment Options of Nephropathic Cystinosis

Nephropathic cystinosis is a severe, monogenic systemic disorder that presents early in life and leads to progressive organ damage, particularly affecting the kidneys. It is caused by mutations in the CTNS gene, which encodes the lysosomal transporter cystinosin, resulting in intralysosomal accumulation of cystine. Recent studies demonstrated that the loss of cystinosin is associated with disrupted autophagy dynamics, accumulation of distorted mitochondria, and increased oxidative stress, leading to abnormal proliferation and dysfunction of kidney cells. We discuss these molecular mechanisms driving nephropathic cystinosis. Further, we consider how unravelling molecular mechanisms supports the identification and development of new strategies for cystinosis by the use of small molecules, biologicals, and genetic rescue of the disease in vitro and in vivo.

Free sialic acid storage disorder: Progress and promise

Lysosomal free sialic acid storage disorder (FSASD) is an extremely rare, autosomal recessive, neurodegenerative, multisystemic disorder caused by defects in the lysosomal sialic acid membrane exporter SLC17A5 (sialin). SLC17A5 defects cause free sialic acid and some other acidic hexoses to accumulate in lysosomes, resulting in enlarged lysosomes in some cell types and 10-100-fold increased urinary excretion of free sialic acid. Clinical features of FSASD include coarse facial features, organomegaly, and progressive neurodegenerative symptoms with cognitive impairment, cerebellar ataxia and muscular hypotonia. Central hypomyelination with cerebellar atrophy and thinning of the corpus callosum are also prominent disease features. Around 200 FSASD cases are reported worldwide, with the clinical spectrum ranging from a severe infantile onset form, often lethal in early childhood, to a mild, less severe form with subjects living into adulthood, also called Salla disease. The pathobiology of FSASD remains poorly understood and FSASD is likely underdiagnosed. Known patients have experienced a diagnostic delay due to the rarity of the disorder, absence of routine urine sialic acid testing, and non-specific clinical symptoms, including developmental delay, ataxia and infantile hypomyelination. There is no approved therapy for FSASD. We initiated a multidisciplinary collaborative effort involving worldwide academic clinical and scientific FSASD experts, the National Institutes of Health (USA), and the FSASD patient advocacy group (Salla Treatment and Research [S.T.A.R.] Foundation) to overcome the scientific, clinical and financial challenges facing the development of new treatments for FSASD. We aim to collect data that incentivize industry to further develop, obtain approval for, and commercialize FSASD treatments. This review summarizes current aspects of FSASD diagnosis, prevalence, etiology, and disease models, as well as challenges on the path to therapeutic approaches for FSASD.

Newborn screening for spinal muscular atrophy in Germany: clinical results after 2 years

Background

Spinal muscular atrophy (SMA) is the most common neurodegenerative disease in childhood. Since motor neuron injury is usually not reversible, early diagnosis and treatment are essential to prevent major disability. Our objective was to assess the impact of genetic newborn screening for SMA on outcome.

Methods

We provided clinical data from 43 SMA patients, identified via polymerase chain reaction of the SMN1 gene from dried blood spots between January 2018 and January 2020 in Germany. Follow-up included neurophysiological examinations and standardized physiotherapeutic testing.

Results

Detection of SMA with newborn screening was consistent with known incidence in Germany. Birth prevalence was 1:6910; 39.5% had 2 SMN2 copies, 23% had 3 SMN2 copies, 32.5% had 4 copies, and 4.5% had 5 copies of the SMN2 gene. Treatment with SMA-specific medication could be started at the age of 14–39 days in 21 patients. Pre-symptomatically treated patients remained throughout asymptomatic within the observation period. 47% of patients with 2 SMN2 copies showed early, presumably intrauterine onset of disease. These patients reached motor milestones with delay; none of them developed respiratory symptoms. Untreated children with 2 SMN2 copies died. Untreated children with 3 SMN2 copies developed proximal weakness in their first year. In patients with ≥ 4 SMN2 copies, a follow-up strategy of “watchful waiting” was applied despite the fact that one of them was treated from the age of 6 months. Two infant siblings with 4 SMN2 copies were identified with a missed diagnosis of SMA type 3.

Conclusion

Identification of newborns with infantile SMA and prompt SMA-specific treatment substantially improves neurodevelopmental outcome, and we recommend implementation in the public newborn screening in countries where therapy is available. Electrophysiology is a relevant parameter to support the urgency of therapy. There has to be a short time interval between a positive screening result and referral to a therapy-ready specialized treatment center.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01783-8.

Establishing an objective biomarker for corneal cystinosis using a threshold-based Spectral domain optical coherence tomography imaging algorithm

PURPOSE

The purpose of the present study was to establish a semi-automated threshold-based image segmentation algorithm to detect and objectively quantify corneal cystine crystal deposition in ocular cystinosis with anterior segment optical coherence tomography (AS-OCT).

METHODS

This prospective, observational, comparative study included 88 eyes of 45 patients from the German Cystinosis Registry Study as well as 68 eyes of 35 healthy control subjects. All eyes were imaged with AS-OCT (Cirrus HD-OCT 5000, Carl Zeiss Meditec AG, Jena, Germany). As an initial step, B-scan images were subjectively analysed for typical changes in morphology in comparison to healthy controls. Based on the experience gained, an objective semi-automated B-scan image segmentation algorithm was developed using a grey scale value-based threshold method to automatically quantify corneal crystals.

RESULTS

On AS-OCT B-scans, corneal crystals appeared as hyperreflective deposits within the corneal stroma. The crystals were distributed either in all stromal layers (43 eyes, 49%) or confined to the anterior (23 eyes, 26%) or posterior stroma (22 eyes, 25%), respectively. The novel automatic B-scan image segmentation algorithm was most efficient in delineating corneal crystals at higher grey scale thresholds (e.g. 226 of a maximum of 255). Significant differences in suprathreshold grey scale pixels were observable between cystinosis patients and healthy controls (p < 0.001). In addition, the algorithm was able to detect an age-dependent depth distribution profile of crystal deposition.

CONCLUSION

Objective quantification of corneal cystine crystal deposition is feasible with AS-OCT and can serve as a novel biomarker for ocular disease control and topical treatment monitoring.

Spinal muscular atrophy (5qSMA): best practice of diagnostics, newborn screening and therapy

Proximal spinal muscular atrophy (SMA) is an autosomal-recessive inherited neuromuscular disorder caused by the degeneration of alpha motor neurons in the anterior horn of the spinal cord. Patients show hypotonia, muscular atrophy and weakness of voluntary proximal muscles. SMA is one of the most common genetic diseases, with a frequency of about 1 in 7,000 newborns in Germany. The vast majority of patients carry a homozygous deletion of exons 7 and 8 of the survival motor neuron (SMN) 1 gene on chromosome 5q13.2; only about 3–4 % of patients are compound heterozygous for this common mutation and an additional subtle mutation in SMN1. The severity of the disease is mainly influenced by the copy number of the highly homologous SMN2.

Since the discovery of the underlying genetic defect 25 years ago, both the diagnostics of SMA and its treatment have undergone constant and in recent times rapid improvements. SMA has become one of the first neuromuscular disorders with effective therapies based on gene targeted strategies such as splice correction of SMN2 via antisense oligonucleotides or small molecules or gene replacement therapy with a self-complementary adeno-associated virus 9 expressing the SMN1-cDNA. With the availability of treatment options, which are most effective when therapy starts at a pre-symptomatic stage, a newborn screening is indispensable and about to be introduced in Germany. New challenges for diagnostic labs as well as for genetic counsellors are inevitable.

This article aims at summarising the current state of SMA diagnostics, treatment and perspectives for this disorder and offering best practice testing guidelines to diagnostic labs.

Genetic testing offer for inherited neuromuscular diseases within the EURO-NMD reference network: A European survey study

The genetic diagnostics of inherited neuromuscular diseases (NMDs) is challenging due to their clinical and genetic heterogeneity. We launched an online survey within the EURO-NMD European Reference Network (ERN) to collect information about the availability/distribution of genetic testing across 61 ERN health care providers (HCPs). A 17 items questionnaire was designed to address methods used, the number of genetic tests available, the clinical pathway to access genetic testing, the use of next-generation sequencing (NGS) and participation to quality assessment schemes (QAs). A remarkable number of HCPs (49%) offers ≥ 500 genetic tests per year, 43,6% offers 100-500 genetic tests per year, and 7,2% ≤ 100 per year. NGS is used by 94% of centres, Sanger sequencing by 84%, MLPA by 66% and Southern blotting by 36%. The majority of centres (60%) offer NGS for all patients that fulfil criteria for NMD of genetic origin. Pipelines for NGS vary amongst centres, even within the same national system. Referral of patients to genetic laboratories by specialists was frequently reported (58%), and 65% of centres participates in genetic testing QAs. We specifically evaluated how many centres cover SMA, DMD, Pompe, LGMDs, and TTR genes/diseases genetic diagnosis, since these rare diseases benefit from personalised therapies. We used the Orphanet EUGT numbers, provided by 82% of HCPs. SMA, DMD, LGMD, TTR and GAA genes are covered by EUGTs although with different numbers and modalities. The number of genetic tests for NMDs offered across HCPs National Health systems is quite high, including routine techniques and NGS. The number and type of tests offered and the clinical practices differ among centres. We provided evidence that survey tools might be useful to learn about the state-of-the-art of ERN health-related activities and to foster harmonisation and standardisation of the complex care for the rare disease patients in the EU.