Advancement in management of muscular dystrophy

1. Recent Advances in
Management of
Muscular Dystrophy
DR. VAIBHAV SOMVANSHI
DM RESIDENT(NEUROLOGY)
GMC,KOTA

2. Introduction
• Muscular dystrophy -Refers to heterogeneous group of genetic diseases associated
with a primary muscle defect
• Leads to progressive muscle wasting and consequent loss of muscle function
• Pathologically- patient have degeneration and regeneration of muscle fibres and
necrosis
 Therapeutic Advances in Muscular Dystrophy. ANN NEUROL 2013;74:404–411

3. Muscular Dystrophies
• Disruption of the dystrophin-
glycoprotein complex
• DMD/BMD
• CMDs (most)
• LGMDs (some)
• Disruption of gene
expression or chromosomal
organization
• FSHD
• EDMD
• Oculopharyngeal dystrophy
• Myotonic dystrophy

4. Genetic testing
• Identifyning the causative gene to establish diagnosis
• To identify the carrier state
• To determine a prenatal diagnosis
Genetic testing has super-seeded muscle biopsy because it is non invasive
and accurate
 Risk assessment and genetic counseling in families with DMD. Acta Myologica • 2012; XXXI: p. 179-183

5. Recent Advances in Management
• Current management does not offer a cure
• Focuses on delaying the disease progression and relieving symptoms
Two major concepts for management have been established:
• Reversing a primary defect(restoring original function of gene)
• Targeting secondary disease outcomes
Kinga I. Gawlik.Review At the Crossroads of Clinical and Preclinical Research for Muscular Dystrophy—Are We Closer to Effective Treatment for Patients. Int. J. Mol. Sci. 2018.

6. Gene manipulation techniques
Reversing the primary defect-more beneficial (mice models)
• Either not applicable in humans
• Gene restoration in patients has encountered obstacles-
Inefficient gene delivery
low expression levels
Immune response towards new antigens,
Alternations of patients’ genome, toxicity
 Kinga I. Gawlik.Review At the Crossroads of Clinical and Preclinical Research for Muscular Dystrophy. Int. J. Mol. Sci. 2018.

7. Targeting secondary defects- require modification of multiple cellular processes
• Boosting regeneration
• Inhibiting cell death and fibrosis
• Modulating inflammation metabolism
• Protein turnover
Current consensus-combination therapy targeting both the primary and
secondary defects of the disease.
 Kinga I. Gawlik.Review At the Crossroads of Clinical and Preclinical Research for Muscular Dystrophy. Int. J. Mol. Sci. 2018.

8. Approaches for primary defects
• Gene therapy
• Stem cell therapy
• Protein therapy
• Mutation repair therapies
Much of research regarding treatment has focused on DMD because of severity
and relatively high frequency
 Kinga I. Gawlik.Review At the Crossroads of Clinical and Preclinical Research for Muscular Dystrophy Int. J. Mol. Sci. 2018.

9. Virus Delivery
Adeno-associated viruses (AAV) -most promising gene delivery vehicles for
treating dystrophic muscles
• Due to low pathogenicity
• The ability to infect non-dividing cells,
• Reasonable packaging capacity (app. 5 kb)
• Effectiveness in transducing skeletal muscles after both i/m ,i/v injections
 Gregorevic, P. Systemic Delivery of Genes to Striated Muscles Using Adeno-Associated Viral Vectors. Nat. Med. 2004, 10, 828–834

10. AAV therapy also be tested in patients
• Limb-girdle MD type 2D, 2B, 2I,
• FKRP-deficient congenital MD
There are no FDA-approved gene therapy products
 Gregorevic, P. Systemic Delivery of Genes to Striated Muscles Using Adeno-Associated Viral Vectors. Nat. Med. 2004, 10, 828–834

11. CRISPR/Cas9 Genome Editing
• Single-guide RNA (sgRNA) guides Cas9 endonuclease into a specific site
• Generates double-strand breaks &DNA repair then takes place
• Exogenous template provides homology-directed repair
• Precisely modify the genome at a target locus
 Long, C.Prevention of Muscular Dystrophy in Mice by Crispr/Cas9-Mediated Editing of Germline DNA. Science 2014, 345, 1184–118

12. Gene editing: CRISPR/Cas9
• In vitro restoration of the gene function by CRISPR/Cas9 editing in
myoblasts using pluripotent stem cells from DMD patients.
• Delivered via a viral vector.
• Potential treatment in humans, although still with the immune-related issues
seen with other therapies.
Tracey Willis, Recent advances in the treatment of Duchenne muscular dystrophy, Paediatrics and Child Health, Volume 31, Issue 9, 2021, Pages 359-363

13. Cell Therapy
• Evidence has been accumulating for the stem cell dysfunction
• Eventually leads to inefficient muscle regeneration and contributes to loss of muscle
function.
• Cell therapy can be utilized for cell replacement
• Offering the potential to reverse muscle atrophy
• Could be used for the correction of the primary genetic defect.
 Benedetti, S.; Hoshiya, H.; Tedesco, F.S.Exploiting Novel Gene and Cell Therapy Strategies for Muscular Dystrophies. FEBS J. 2013, 280, 4263–4280.

14. Numerous cell types have shown myogenic potential
• Muscle satellite cells
• Muscle-derived stem cells (mesenchymal-like stem cells residing
in muscle)
• Cells derived from bone marrow
• Vessel wall (mesoangioblasts, pericytes) & dermis
Both autologous and allogeneic cell transplants are considered.

15. Pit falls with cell therapy
• Difficulties with cell isolation
• Expansion,efficient delivery and engraftment
• Cell survival, and stable expression of a therapeutic protein
Autologous cell therapies(mesoangioblasts, myoblasts, bone marrow cells, mesenchymal cells)
• Duchenne/Becker
• Oculopharyngeal MD
• Fascioscapulohumeral MD
 Benedetti, S.; Hoshiya, H.; Tedesco, F.S.Exploiting Novel Gene and Cell Therapy Strategies for Muscular Dystrophies. FEBS J. 2013, 280, 4263–4280.

16. Protein Therapy
• Based on delivery of a therapeutic protein into diseased muscle.
• Advantage-Escaping involvement of genetic material and gene expression-
related steps
• Ideal for quick implementation.

17. Pit falls in protein therapy
• Stability of therapeutic proteins and long-term effect of protein therapy.
• Protein delivery into diseased muscle is as tricky as gene delivery
• Immune response towards a foreign antigen.
• Large-scale production of human recombinant proteins for therapeutic
injections
 Rooney, J.E.; Gurpur, P.B.; Burkin, D.J. Laminin-111 Protein Therapy Prevents Muscle Disease in the MdxMouse Model for Duchenne Muscular Dystrophy

18. Upregulation of utrophin
• Utrophin is naturally expressed and upregulated in DMD patients.
• Utrophin protein like dystrophin, is found in many tissues, not just muscle
and brain.
• Utrophin is found at the neuromuscular and myotendinous junctions.
• Unfortunately, the phase 2 trial with ezutromid (Utrophin modulator) didn’t
show promising result.
Tracey Willis, Recent advances in the treatment of Duchenne muscular dystrophy, Paediatrics and Child Health, Volume 31, Issue 9, 2021, Pages 359-363

19. Endogenous Up-Regulation of Paralogous Genes
• Triggering muscle-specific endogenous up-regulation of homologous/therapeutic
protein
• Already expressed in a patient body (either in low levels in muscle or in other
tissues)
Increasing the expression of a gene could be achieved
• Small-compound drugs that interact with promotor sequences of a gene of interest
• Specifically trigger the transcription machinery
 Kinga I. Gawlik.Review At the Crossroads of Clinical and Preclinical Research for Muscular Dystrophy—Are We Closer to Effective Treatment for Patients. Int. J. Mol.
Sci. 2018.

20. Advantages
• Provides solution to various problems arising from the gene
therapy strategies
• Solves the issue of immune response towards foreign antigens
• Small artificial molecules have favorable absorption, distribution,
and metabolism
• Advantages in terms of delivery, stability, and availability
 Kinga I. Gawlik.Review At the Crossroads of Clinical and Preclinical Research for Muscular Dystrophy—Are We Closer to Effective Treatment for Patients. Int. J.
Mol. Sci. 2018.

21. Mutation Repair
• Rapid development and significant improvement of genomics technologies
• Opened new avenues for targeting the primary genetic defect through
genome editing
• Alternative to the classical gene therapy approach.

22. Exon Skipping
• Aimed at reframing the disrupted transcripts using antisense oligonucleotides
• Modulation of splicing results in an expression of truncated, but functional,
protein.
• Not all mutations are suitable for exon skipping
• Certain mutations in the dystrophin gene (e.g., in exon 51, approximately 13% of
patients)
 Eteplirsen for the Treatment ofDuchenne Muscular Dystrophy. ANN NEUROL 2013;74:637–647

23. DMD Gene
• Largest gene – 427kD
• 79 exons
• Most common deletion>small mutation>duplication
• In DMD - ‘hot spot’ clustering of the mutations in the exon 43 to 55
• Exon 51 (14%), exon 53 (10.1%), exon 45 (9%), exon 43(7.5%) and exon 44
(7.1%).
Tracey Willis, Recent advances in the treatment of Duchenne muscular dystrophy, Paediatrics and Child Health, Volume 31, Issue 9, 2021, Pages 359-363

24. Eteplirsen
• Exon 51 skipping (13 percent of patients with DMD)
• Increased dystrophin in muscle and increased walking performance on timed
tests in patients
• USFDA granted accelerated approval of eteplirsen in September 2016
• Dose-30 mg/kg once a week by intravenous infusion over 35 to 60 minutes
 Eteplirsen for the Treatment of Duchenne Muscular Dystrophy. ANN NEUROL 2013;74:637–647

25. • 24-week (12 patients) in a 1:1:1 ratio to weekly dosing of intravenous
eteplirsen 30 mg/kg, eteplirsen 50 mg/kg, or placebo.
• Followed by a 24 week extension phase during which all subjects
received eteplirsen.
• At 48 weeks, those assigned to eteplirsen 50 mg/kg walked a
significantly greater distance in the six-minute walk test compared with
the placebo/delayed eteplirsen group.
 Eteplirsen for the Treatment of Duchenne Muscular Dystrophy. ANN NEUROL 2013;74:637–647

26. Other Exon skippers
• Golodirsen – exon 53 skipping – 10.1% - 30 mg/kg once a week by
intravenous infusion over 35 to 60 minutes (USFDA approval- December
2019)
• Viltolarsen – exon 53 - 80 mg/kg once a week, given by intravenous
infusion over 60 minutes (USFDA approval - August 2020)
• Casimersen – exon 45 – 9% - 30 mg/kg once weekly given by intravenous
infusion over 35 to 60 minutes (USFDA approval - February 2021)

27. (1.15 lakh/vial) (1.75 lakh/vial) (15000/vial)

28. Suppression of Stop Codons
• Nonsense mutations give rise to in-frame stop codons in messenger RNA
coding regions
• Can be pharmacologically targeted
• Drug-induced translational read-through of the premature codon stop
enables the expression of full-length functional protein.
• 11-13% of DMD patients who have nonsense mutations
 McDonald, C.M.; et al. Ataluren in Patients with Nonsense Mutation Duchenne Muscular Dystrophy (Act Dmd). Lancet 2017, 390, 1489–1498

29. Ataluren
• First drug conditionally approved for DMD and eligible for use now in children
aged 2 years and above who are ambulant (August 2014 by European Union)
• Promotes ribosomal read-through of nonsense (stop) mutations
• Allowing bypass of the nonsense mutation
• Continuation of the translation process to production of a functioning protein

30. • Available in sachets in granular form
• Dosing -10 mg/kg in the morning, 10 mg/kg at midday, and 20
mg/kg in the evening, for a total daily dose of 40 mg/kg.
• Adverse effect-vomiting ,decreased appetite, weight loss,
hypertriglyceridemia, headache, hypertension
 McDonald, C.M.; et al. Ataluren in Patients with Nonsense Mutation Duchenne Muscular Dystrophy (Act Dmd). Lancet 2017, 390, 1489–1498

31. Targeting Secondary Defects of Muscular
Dystrophy
• Complicated character of dystrophic disorders is largely dictated by
secondary pathologies
• They severely exacerbate the dystrophic phenotype
• This makes the disease difficult to target comprehensively
Kinga I. Gawlik. Review At the Crossroads of Clinical and Preclinical Research for Muscular Dystrophy—Are We Closer to Effective Treatment for Patients. Int. J. Mol.
Sci. 2018.

32. Prednisone & deflazacort
• Efficacy of deflazacort for DMD is similar to prednisone.
• Studies reported comparable improvements in muscle function, pulmonary
function, and orthopedic outcomes
• DEFLAZACORT less chances of weight gain and cushanoid features
• Prednisolone daily dosing at 0.75 mg/kg strength
• Deflazacort is generally dosed at 0.9 mg/kg per day.
 Bonifati MD et al. A multicenter, double-blind, randomized trial of deflazacort versus prednisone in Duchenne muscular dystrophy. Muscle Nerve 2000; 23:1344

33. Corticosteroid Conversion

35. Creatine
• Potential to increase muscle strength in neuromuscular disorders and
muscular dystrophies.
• Creatine was well tolerated with no evidence of renal or liver dysfunction.
• Creatine treatment was not associated with significant improvement on
functional measures or activities of daily living.
 Louis M, Lebacq J, Poortmans JR, et al. Beneficial effects of creatine supplementation in dystrophic patients. Muscle Nerve 2003; 27:604

36. Myostatin inactivation
• Myostatin is a protein that has an inhibitory effect on muscle growth.
• Antibodies to myostatin also have a beneficial effect(animal models)
• Myostatin inactivation-therapeutic target to increase muscle bulk and
strength in muscular dystrophies diseases
• Clinical trials of myostatin inhibitors are underway
 Bogdanovich S, Krag TO, Barton ER, et al. Functional improvement of dystrophic muscle by myostatin blockade. Nature 2002; 420:418

38. Supportive treatment
• Physiotherapy
• Non-invasive ventilation support
• Manually and mechanically-assisted coughing techniques
• Posture correcting surgeries
 Kinga I. Gawlik.Review At the Crossroads of Clinical and Preclinical Research for Muscular Dystrophy—Are We Closer to Effective Treatment
for Patients. Int. J. Mol. Sci. 2018.

39. • Use of equipment that supports ambulation, maintains posture,
and prevents contractures (braces, mobility aids, night splints)
• Tube feeding, enterogastrostomy
• Proper diet rich in supplements.

40. Genetic counselling
Identifying carriers
• Once a mutation is identified, carrier analysis can be performed for the
mother.
• Confirming carrier status in the mother affects family planning
• Her daughters, sisters, cousins and aunts are potentially at risk of being a
carrier.
• Even when the mother is not a carrier, still possible she has germline-
mosaicism for the mutation , still at risk of having a second son with DMD
 Risk assessment and genetic counseling in families with DMD. Acta Myologica • 2012; XXXI: p. 179-183

41. Reproductive options
Pre-natal diagnosis-Women now have the option to screen for DMD/BMD prior to or
during pregnancy
• Chronic villous sampling
• Amniocentesis
Cells from the fetus can be tested to determine if they have genetic mutation and
proceed accordingly
 Risk assessment and genetic counseling in families with DMD. Acta Myologica • 2012; XXXI: p. 179-183

42. Non invasive Prenatal diagnosis
• Taking a sample of blood from mother
• Testing for free fetal DNA
Pre-implantation genetic diagnosis
• Option to use IVF and then test early embryos
• Allow unaffected embryo to transfer to mother
 Risk assessment and genetic counseling in families with DMD. Acta Myologica • 2012; XXXI: p. 179-183

43. Conclusions
• Muscular dystrophies have debilitating consequences needs multidisciplinary
treatment approach.
• Newer drugs & therapies have become available but still out of reach to maximum
population and their efficacy is still debatable.
• Still newer drugs and therapeutic options need to be explored for better
management.

45. Refrences
• Kinga I. Gawlik.Review At the Crossroads of Clinical and Preclinical Research for Muscular
Dystrophy—Are We Closer to Effective Treatment for Patients. Int. J. Mol. Sci. 2018.
• Jordi Díaz-Manera. Muscle MRI in muscular dystrophiesActa Myologica • 2015; XXXIV: p.
95-108
• REKHA MITTAL. Duchenne Muscular Dystrophy:Changing Strategies in Diagnosis,
Prevention and Therapeutics,2015
• Therapeutic Advances in Muscular Dystrophy. ANN NEUROL 2013;74:404–411
• Risk assessment and genetic counseling in families with DMD. Acta Myologica • 2012;
XXXI: p. 179-183
• WWW.UPTODATE.COM

46. • Losartan , epeleronone-tested in clinical trials for the treatment of
cardiomyopathy of DMD patients
• Thrombospondin-4- increased expression have been shown to have a
protecting effect and promote skeletal muscle integrity
 Accorsi, A. Igf-1/Gh Axis Enhances Losartan Treatment in Lama2-Related Muscular Dystrophy. Hum. Mol. Genet. 2016, 25, 4624–4634.