Open-label Extension Study in Paediatric Patients Who Have Completed the MEX-NM-301 Study.

1. Is the biology right?

• Somatic driver evidence: no · None of SCN1A, SCN5A, SCN4A has somatic-mutation evidence in myotonic dystrophy type 1

  Rule: Open Targets has somatic-mutation evidence for the target in this cancer. Source: Open Targets: SCN1A in myotonic dystrophy type 1, 2026-11-11
• Human genetic evidence: no · No germline or somatic evidence for SCN1A, SCN5A, SCN4A in myotonic dystrophy type 1

  Rule: Any germline or somatic human genetic evidence for the target in this cancer, counted apart from animal-model and literature evidence. Source: Open Targets: SCN1A in myotonic dystrophy type 1, 2026-11-11
• Pediatric target: no · Not on the FDA list

  Rule: Target is on FDA's Pediatric Molecular Target List (relevant targets); membership alone neither requires nor waives a study. Source: FDA Pediatric Molecular Target List (Listed as February 2026 on the FDA Pediatric Oncology page; the file served is 9.7.22_the_relevant_molecular_target_list.xlsx, whose Summary of Changes sheet is headed 'SEPTEMBER 2022 UPDATE' (footnote date 2022-09-01)), 2026-11-11
• Haematologic cancer: no · Solid tumour

  Rule: From the indication, or the registry conditions when no indication matches. Source: ClinicalTrials.gov NCT04622553, 2026-11-11

  Published context: Likelihood of approval from phase 1: 7.5% haematologic vs 4.6% solid (BIO / Informa / QLS 2021, 2011–2020). Population-level, not a prediction.

• SCN1A (via Mexiletine): Evidence types in myotonic dystrophy type 1: animal_model, clinical; animal_model listed separately from human genetics. Datasources: clinical_precedence, impc. · Open Targets: SCN1A in myotonic dystrophy type 1
• SCN5A (via Mexiletine): Evidence types in myotonic dystrophy type 1: literature, animal_model, clinical; literature and animal_model listed separately from human genetics. Datasources: clinical_precedence, europepmc, impc. · Open Targets: SCN5A in myotonic dystrophy type 1
• SCN4A (via Mexiletine): Evidence types in myotonic dystrophy type 1: literature, animal_model, clinical; literature and animal_model listed separately from human genetics. Datasources: clinical_precedence, impc, europepmc. · Open Targets: SCN4A in myotonic dystrophy type 1

• Not loaded on this app yet: Normal-tissue expression in vital organs. Source: Human Protein Atlas (ticket 36).
• Not loaded on this app yet: Pan-essential in cell lines. Source: DepMap (ticket 36).
• Not loaded on this app yet: Approved drug on this target. Source: Drugs@FDA (ticket 30).

2. Can the result be trusted?

• Randomised: no · Single group

  Rule: Registry allocation field. Source: ClinicalTrials.gov NCT04622553, 2026-11-11
• Small denominator: yes · 12 enrolled; each patient moves a rate by 100 ÷ 12 = 8.3 points

  Rule: Enrolment under 30; the arithmetic is shown, not a benchmark. Source: ClinicalTrials.gov NCT04622553, 2026-11-11
• Primary endpoint is overall survival: no · Assess the long-term safety and tolerability of mexiletine by AEs; Assess the long-term safety and tolerability of mexiletine by hand relaxation; Assess the long-term safety and tolerability of mexiletine measurement of AESI (and 2 more)

  Rule: A registered primary outcome measure names overall survival. Source: ClinicalTrials.gov NCT04622553, 2026-11-11

  Published context: Non-OS primary endpoint: odds ratio 2.79 for a positive phase 3 (Otsuka 2021, 400 phase 3 oncology trials, to 2020). Shown with the next figure: a surrogate is easier to hit, and often a weak guide to survival.

  Published context: 52% of surrogate-to-OS correlations are low (Prasad 2015, published to 2014). Shown with the figure above.
• Results overdue: no · Primary completion 2026-06-04, 5 months ago; within 12 months

  Rule: Primary completion (actual) more than 12 months ago and no results posted to the registry. Source: ClinicalTrials.gov NCT04622553, 2026-11-11

• Not loaded on this app yet: Treated and evaluable counts, assessor, confirmed response, follow-up and data cutoff. Source: Readout extraction (ticket 32).
• Not loaded on this app yet: Primary endpoint changed between registry versions. Source: Registry versions in the store (ticket 32).

3. What must it beat?

• Not loaded on this app yet: Control-arm result and approved therapies for the same segment, with label links. Source: Drugs@FDA, FDA labels and readouts (tickets 30, 32).

4. Too crowded, or too late?

• Stopped on this target: 125 terminated, withdrawn or suspended trials of drugs against SCN1A; 19 give no reason. Reasons are quoted as the registry gives them on the target page. · SCN1A: what already stopped

• Not loaded on this app yet: Programs on the target by phase and months behind the leader. Source: Programs and Drugs@FDA (ticket 33).

5. Can it be approved, and stay approved?

• Single-country: yes · The only site is in France

  Rule: All listed sites are in one country; the share of US sites is shown. Source: ClinicalTrials.gov NCT04622553, 2026-11-11
• EU paediatric investigation plan: yes · EMEA-002012-PIP01-16-M05 (Mexiletine hydrochloride, Treatment of myotonic disorders): PM: decision on the application for modification of an agreed PIP, 19 Jul 2024

  Rule: An EMA PIP decision (agreement, modification or waiver) lists the drug as its active substance, exact name. Source: EMA EMEA-002012-PIP01-16-M05, 2026-11-11
• EU orphan designation: yes · EU/3/13/1126 positive 7 Jun 2013: Treatment of non-dystrophic myotonia; EU/3/14/1353 positive 19 Nov 2014: Treatment of myotonic disorders; EU/3/13/1189 positive 7 Oct 2013: Treatment of myotonic disorders

  Rule: An EU orphan designation lists the drug as its active substance (exact name) or belongs to a medicine that does; withdrawn and expired designations are listed with their status. Source: EMA data download (dated snapshot), 2026-11-11
• Authorised in the EU: yes · Namuscla: authorised since 18 Dec 2018, orphan medicine

  Rule: An EMA medicine record lists the drug as its active substance or INN, exact name; national-only authorisations are not in this file. Source: EMA EPAR Namuscla, 2026-11-11
• FDA orphan designation: not published · FDA's orphan designation database turns away automated requests, so this app does not read it; search it by hand at the link

  Rule: Would be: an FDA orphan designation names the drug. Source: FDA orphan designations search
• FDA pediatric oncology approval: no · FDA's table lists no pediatric approval of Mexiletine

  Rule: FDA's Pediatric Oncology Drug Approvals table names the drug. Source: FDA Pediatric Oncology Drug Approvals (content current as of 2026-03-03), 2026-11-11
• Registered studies open to children: yes · 7 interventional studies of Mexiletine include patients under 18; 3 are recruiting, not yet recruiting or active

  Rule: The registry's age group includes Child (birth to 17 years), which also counts studies that set no minimum age. Source: ClinicalTrials.gov search, 2026-11-11

• Caveat: Site counts are not patients per country, and trials registered only outside ClinicalTrials.gov are not covered. Where the sites are is a fact about the record, not a judgement of its quality.
• Cited case: In February 2022 FDA asked its Oncologic Drugs Advisory Committee whether sintilimab's application, resting on ORIENT-11, a phase 3 run only in China, needed further trials showing it applies to US patients and US practice. One case, not a rule. · FDA, ODAC 10 Feb 2022, draft questions
• Rare pediatric disease voucher: FDA, content current as of 29 Apr 2026: “As of February 3, 2026, enactment of the Consolidated Appropriations Act, 2026, the rare pediatric disease PRV program will sunset after September 30, 2029. FDA may not award any PRVs under this program after September 30, 2029.” Voucher sale prices are not shown here; they appear only as company-reported news. · FDA: Rare Pediatric Disease Designation and Priority Review Voucher Programs

• Not loaded on this app yet: Precedent approvals for target, modality and endpoint; accelerated-approval status. Source: Drugs@FDA and FDA accelerated-approval tables (ticket 30).

6. Can the sponsor finish?

• Sponsor: Lupin Ltd. (industry) · ClinicalTrials.gov NCT04622553
• principal investigator: Christine Barnérias, MD, Hopital universitaire Necker-Enfants Malades · Person page

• Not loaded on this app yet: Filed cash, quarterly spend and the runway arithmetic. Source: SEC XBRL company facts (ticket 37).
• Not loaded on this app yet: Sponsor's completed vs stopped oncology trials and results-reporting record. Source: Registry, by company (ticket 37).

What public data cannot tell you

Public records cannot show: sales forecasts; a probability of success for this asset; full deal terms and net prices; FDA designations and action dates before approval (shown only as company-reported); clinical holds unless the company disclosed them; manufacturing; patents on unapproved drugs; whether preclinical findings have been replicated.