Genetic Newborn Screening for Cystinosis and Spinal Muscular Atrophy
Condition: Cystinosis; Cystinosis, Nephropathic; Spinal Muscular Atrophy
MeSH terms: Muscular Atrophy; Muscular Atrophy, Spinal; Cystinosis; Atrophy
Study type: Interventional

Summary: 
      Newborn screening in Germany is a voluntary program. Cystinosis and spinal muscular atrophy
      (SMA) are rare autosomal recessive diseases. They are inherited in an autosomal recessive
      manner, i.e. both parents carry a defective gene. Neither disease can be detected early by
      the methods established in routine newborn screening. However, common genetic mutations are
      known for both diseases.

      The aim of the study presented here is to provide the scientific basis for molecular genetic
      newborn screening for cystinosis and SMA. In particular, to investigate whether inclusion of
      these diseases in general newborn screening should be recommended.

      The participating screening laboratories for this project are Labor Becker & Kollegen,
      Munich, Germany and Screening Laboratory Hannover, Germany. Hospitals that send their dry
      blood spot cards for routine newborn screening to these laboratories will receive an offer to
      participate in the pilot project. Participation is free of charge.

      Parents who wish to participate in this pilot project will receive an information sheet
      explaining the screening process and objectives. A parent and the treating physician sign the
      information sheet as documentation of informed consent. Their signature and informed consent
      are required for the pilot.

      Routine NBS according to German pediatric guidelines involves the collection of dried blood
      spot cards 36-72 hours after birth. Molecular genetic screening in the pilot project will be
      performed with the same dried blood spot card used for routine newborn screening.

      In cystinosis, genetic testing for the 3 most common mutations in Germany will be performed.
      In SMA, a homozygous deletion of exon 7 in the SMN gene is detected by a PCR test. The
      molecular genetic test is performed on the same day as routine newborn screening.Normal
      findings are not reported to parents. However, they can contact the laboratories to inquire
      about them.

      Parents of newborns with two mutations in the cystinosis gene or with a homozygous deletion
      of exon 7 in the SMN gene are immediately informed of the disease by a physician. Further
      diagnostics to confirm the disease will be organized close to home.

      The study started on Jan. 15, 2018, and recruitment was completed on Sept. 30, 2022.
    

Detailed description: 
      Population-based newborn screening (NBS) is an important public health program that has
      vastly improved the course of several diseases through early detection. The selection of
      screened disorders generally follows the 10 principles outlined by Wilson and Jungner. In
      Germany, NBS has been a voluntary National Health Service program since 1969 which currently
      covers 17 disorders. Current NBS methods, which employ tandem mass-spectrometric analysis of
      newborn dried blood spots, cannot detect many potentially treatable genetic conditions. At
      the same time, molecular-based NBS is increasingly feasible because DNA can be extracted from
      a dried blood spot, next generation sequencing has become economical, and molecular
      diagnostics have greater reliability and increased validity as genetic databases become more
      refined and comprehensive. Nephropathic cystinosis and spinal muscular atrophy (SMA) are
      eligible for molecular-based NBS because effective therapies are available.

      This study will provide a scientific basis for newborn screening for cystinosis and SMA and
      investigate whether inclusion of these diseases in general newborn screening should be
      recommended. By observing identified infants compared to symptomatically diagnosed patients
      outside the pilot project, we will determine whether and to what extent early diagnosis and
      initiation of therapy leads to a more favorable prognosis.

      Cystinosis: Cystinosis is a rare autosomal recessive systemic disease with high morbidity and
      mortality caused by pathogenic variants in the CTNS gene that encodes the lysosomal cystine
      transporter cystinosin, leading to accumulation of cystine within the lysosome. Life-long
      cystine-depleting therapy with oral cysteamine, the only specific therapy for cystinosis,
      along with the availability of renal replacement therapy in childhood, has dramatically
      improved patient outcomes. There is robust evidence that early initiation and sustained
      therapy with cysteamine are both essential for delaying progression to chronic kidney disease
      (CKD) and end-organ damage.

      Currently, the diagnosis of cystinosis is based on the presence of elevated cystine levels in
      white blood cells. This method is unsuitable for NBS.

      Spinal Muscular Atrophy (SMA): Spinal muscular atrophy has a prevalence of approximately
      1:10,000 live births in Germany. It is inherited in an autosomal recessive manner. Newborns
      with spinal muscular atrophy are without clinical symptoms after birth.

      The cause of spinal muscular atrophy is a deletion of exon 7 in the SMN1 gene, the coding
      gene for the "survival motor neuron protein". Homozygous deletion lacks the functional SMN
      protein on which the anterior horn cells in the spinal cord depend. Heterozygous carriers are
      asymptomatic. Lack of the functional SMN protein results in damage to motor neurons at the
      spinal cord level, leading to severe neurogenic remodeling and atrophy of skeletal muscles.

      In addition to the SMN1 gene, humans have an almost identical, adjacently located
      "pseudo-gene," the SMN2 gene. It differs from the SMN1 gene only by 5 single base pairs. The
      SMN2 protein plays no role in healthy humans, since sufficient functional SMN1 protein is
      present. The SMN2 gene contains a molecular switch that can completely shut down the
      expression of the gene. The clinical variability of spinal muscular atrophy is explained by
      differential expression of the SMN2 protein. Thus, the readout of the SMN2 gene including its
      exon 7 by inhibition of the off switch represents a therapeutic target for the treatment of
      SMA patients. The possibility of a therapy to positively influence the course of the disease
      was demonstrated in the placebo-controlled multi-center study with an antisense
      oligonucleotide nusinersen (Spinraza®) from Ionis/Biogen in 2015/2016.

      Diagnosis of the disease in cases of clinical suspicion has been made by targeted testing of
      the SMN1 and SMN2 genes from EDTA blood and DNA isolated therefrom. The test is usually
      performed in genetics laboratories using MLPA (multiplex ligation-dependent probe
      amplification). Because a commercial kit is required for each sample, the test is too costly
      for screening as part of newborn screening.

      Procedure:

      Study population Hospitals in Germany are free to choose which of the 11 certified
      laboratories they send the dry blood spot cards to for newborn screening and whether they
      want to participate in pilot projects.

      In this project, the Becker & Kollegen laboratory in Munich and the Hannover screening
      laboratory are informing their senders about the possibility of adding genetic screening for
      cystinosis (Hannover) or cystinosis and SMA (Munich) to the routinely established newborn
      screening.

      The study population includes newborns whose parents wish to participate in the pilot project
      and have provided written informed consent. An additional information and consent sheet for
      cystinosis and SMA screening is provided, which includes an explanation of the screening
      process and objectives, expected benefits, possible adverse consequences of
      non-participation, and the significance of the test results. Parents are informed that they
      will be informed of normal, unremarkable results only upon request. Consent must be
      documented with the signature of at least one parent and the signature of the informing
      physician on the consent form. The consent form for the pilot project also includes consent
      to share contact information and findings with a specialized center in the event of an
      abnormal screening result.

      In the event of a positive result, the laboratory must first inform the sender and clarify
      whether or not the child is still in hospital. If the child is still undergoing inpatient
      treatment, the sender obtains the initial information from the parents and notifies an expert
      for the corresponding diagnosis. If the child has already been discharged from the hospital,
      the laboratory contacts the appropriate expert directly (Cystinosis: Priv.-Doz. Dr. med.
      Katharina Hohenfellner, Rosenheim; SMA: Prof. Dr. med. Wolfgang Müller-Felber, Munich).

      Sampling Molecular genetic screening is performed using the same dry blood card (drops of
      blood on a filter paper card) as routine NBS. No additional blood collection is required. If
      little material is available, the regular NBS is performed first, followed by screening for
      cystinosis and SMA. According to the pediatric guideline, the blood sample for the NBS should
      be collected between 36 and 72 hours of life.

      In general, for all invalid results (i.e., if the control reaction fails) and for all
      abnormal results the test is repeated internally for confirmation using the available blood
      sample. If the quality of the blood sample is poor (e.g., too little blood), the laboratory
      will request a new blood sample. If there is too little material to perform the required next
      generation sequencing, the laboratory will also request another dried blood sample.

      Measurements and Methods Cystinosis: For cystinosis screening, multiplex PCR was performed at
      the first stage to detect the three most common CTNS mutations in Germany, i.e. a 57kb
      deletion (responsible for about half of cystinosis in Europe and North America)
      c.18_21delGACT, p.T7Ffs*7 and c.926dupG, p.S310Qfs*55 . Heterozygous samples will be
      subjected to amplicon-based next-generation sequencing for 101 pathogenic mutations. This
      approach predicts a detection rate of 96.5%.

      SMA The triplex PCR for the CTNS mutations described above is complemented by another PCR
      that detects exon 7 in the SMN1 gene. With this quadruplex PCR, a specific signal is obtained
      for normal samples (those without or with heterozygous exon 7 deletion in both alleles of the
      SMN1 gene). SMA screening is considered positive if a homozygous exon 7 deletion is detected
      in the SMN1 gene. The absence of PCR amplification indicates the absence of a functional SMN1
      copy, i.e., an affected newborn. Heterozygous individuals cannot be detected by this method
      Detection rate, false positive and false negative results An overall detection rate of more
      than 95% is assumed for both diseases. False negative screening results are unlikely. In
      cystinosis, false negative results are possible due to previously unknown rare mutations or
      patients not carrying any of the three most common mutations. In SMA, patients in whom a
      heterozygous deletion is combined with a point mutation are not considered. In patients with
      symptoms of cystinosis or SMA, further diagnostic tests are performed independently of
      screening.

      False positive screening results are also very unlikely. In cystinosis, a heterozygous sample
      may falsely appear as homozygous due to "allelic dropout" (PCR failure of an allele due to
      mutations in the primer binding region).

      Confirmation of diagnosis Cystinosis: In patients found to have either a homozygous or
      compound heterozygous mutation in a CTNS gene, the diagnosis is confirmed by determining the
      intraleukocytic cystine level from EDTA blood. This sample is sent to the metabolic
      laboratory in Münster within the first 14 days of life.

      SMA: If exon 7 in the SMN1 gene is homozygous, SMA must be assumed (> 50% type I with most
      severe course). In order to classify the severity of SMA, further diagnostics are required by
      recording the number of SMN-2 copies. Another blood sample will be sent by the responsible
      care center to the reference laboratory in Ulm. The verification test results are forwarded
      to the screening laboratory for quality control.

      Care of the affected child Cystinosis: Children with positive cystinosis screening results
      are referred to the nearest metabolic disease center. Therapy with cysteamine will be started
      immediately after the diagnosis is confirmed..

      SMA: Children with positive SMA screening results are referred either to the Center for
      Neuromuscular Diseases in the Social Pediatric Center of the Dr. von Hauner Children's
      Hospital (Bavaria) or to the University Hospitals of Essen and Münster.

      Project scope The project was initially limited to 200,000 samples, with the possibility of
      expansion.
    

Intervention name(s): molecular-based screening
Intervention type(s): Diagnostic Test
Intervention description(s): Test for three mutations in the CTNS gene and one mutation in the SMA1 gene.
Intervention model: Single Group Assignment
Intervention model description: All newborns whose parents have agreed to participate in the pilot project will be tested for three mutations in the CTNS gene and a homozygous deletion of exon 7 in the SMN1-gene.
Masking: None (Open Label)
Primary purpose: Screening
Keywords: Newborn Screening; Screening; Molecular-based Screening