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ORPHA:2609

Isolated complex I deficiency

high confidenceDisorder

Also known as: Isolated NADH-CoQ reductase deficiency · Isolated NADH-coenzyme Q reductase deficiency · Isolated NADH-ubiquinone reductase deficiency · Isolated mitochondrial respiratory chain complex I deficiency

Publications

405

69.5th percentile

Trials

0

Interventional, condition-specific

Researchers

1,396

Distinct authors in sample

Gene link

SLC35G2

Limited

Readiness

4/6

Stages with a signal

Clinical definition (Orphanet)

Isolated complex I deficiency is a rare inborn error of metabolism due to mutations in nuclear or genes encoding subunits or assembly factors of the human complex I (NADH: ubiquinone oxidoreductase) and is characterized by a wide range of manifestations including marked and often fatal lactic , , leukoencephalopathy, pure and hepatopathy with tubulopathy. Among the numerous clinical phenotypes observed are Leigh syndrome, Leber optic and MELAS syndrome.

How rare: How common this is has not been clearly measured.

Orphanet entry

Cross-references

Joined from Mondo / Orphanet. MeSH labels may enter searches; UMLS / OMIM / NCIT are stored for reference.

Additional Mondo synonyms (8)

NADH coenzyme Q reductase deficiency · complex 1 mitochondrial respiratory chain deficiency · isolated NADH-CoQ reductase deficiency · isolated NADH-coenzyme Q reductase deficiency · isolated NADH-ubiquinone reductase deficiency · isolated complex I deficiency · isolated mitochondrial respiratory chain complex I deficiency · mitochondrial respiratory chain complex I deficiency

Research stages

Trial readiness signals

Where this condition sits on an open-data research pipeline — not how close a treatment is, and not medical advice. Empty stages often mean “not in these databases under this Mondo ID,” not “impossible.”

4/6 stages with a signal

No matched interventional trial, but a gene association and an animal model are on record — often described as translation-ready / stalled at the clinical step.

  1. Gene identifiedPresent

    Limited — SLC35G2

  2. LiteraturePresent

    405 matched papers (219 in last 10 years) Source

  3. Phenotype characterisedPresent

    785 HPO annotations (e.g. Decreased activity of mitochondrial complex I; Proximal tubulopathy; Ataxia) Source

  4. Animal modelPresent

    5 genotype models (Mus musculus) Source

  5. Orphan designationNot found

    No FDA or EMA orphan-drug designation matched this disease via UMLS or preferred name Source

  6. Interventional trialNot found

    No matched interventional trial under our ClinicalTrials.gov rules

Biology

Genes and phenotypes

Gene–disease validity from GenCC, plus phenotypes and animal models joined from Monarch Initiative via Mondo ID — not a clinical diagnosis aid.

Do we know what causes it?

Possibly — only limited evidence so far for SLC35G2.

GenCC classification: Limited.

Phenotypes (Monarch / HPO)

785

Associated phenotypes · MONDO:0100133

  • Decreased activity of mitochondrial complex I
  • Proximal tubulopathy
  • Ataxia
  • Lethargy
  • Muscle weakness

Showing 5 of 785 — open Monarch for the full list.

Animal models (Monarch / Alliance)

5

Model associations linked to this Mondo ID

Monarch fetch 2026-07-29

Therapies

Designations, candidates, and chemicals

FDA OOPD and EMA orphan designations, Open Targets clinical candidates, and CTD chemical associations via MyDisease.info. These never change the interventional-trial headline.

Orphan designation (FDA · EMA)

No designation matched this disease via UMLS or preferred name on the FDA OOPD mirror or EMA orphan register. Absence here is not proof that none exists under another wording.

Open Targets candidates

No drugs or clinical candidates returned for this Mondo ID on Open Targets.

CTD chemicals (MyDisease.info)

No CTD chemical associations returned for this Mondo ID.

Literature

Is anyone studying this?

405

405 papers have ever been published on this condition (under this name). For scale, breast cancer has over 700,000. Median papers in the last 10 years for a rare disease in this dataset (publications denominator n=3967) is 59.

405 papers since the earliest indexed year in this search — median last-10-year count for a rare disease in this dataset is 59 (publications denominator n=3967).

219 in the last 10 years · high confidence · 69.5th percentile (publications denominator)

Phrase hits: 325 · MeSH hits: 0

Open Europe PMC search

Who's working on it?

1,396

Distinct author names in 200 sampled papers — named people below.

Who's working on it?

No interventional trial matched this name; these authors publish on it in the sampled literature — a practical starting point for contact.

  1. 01
    Taylor RW21 papers · 2025

    Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK.

    Papers in Europe PMC
  2. 02
    Alston CL15 papers · 2025

    Wellcome Centre for Mitochondrial Research, Translational and Clinical Research Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK.

    Papers in Europe PMC
  3. 03
    Thorburn DR15 papers · 2026

    From the Murdoch Children's Research Institute, Royal Children's Hospital and Department of Paediatrics, University of Melbourne, and.

    Papers in Europe PMC
  4. 04
    Smeitink JA14 papers · 2016

    Centre for Systems Biology and Bioenergetics, Radboud University Medical Center, Nijmegen, The Netherlands Khondrion BV, Nijmegen, The Netherlands Department of Pediatrics, Radboud Center for Mitochondrial Medicine, Radboud University Medical Center, Nijmegen, The Netherlands Jan.Smeitink@Radboudumc.nl.

    Papers in Europe PMC
  5. 05
    Prokisch H13 papers · 2026

    Institute of Human Genetics, Technische Universität München, München, Germany.

    Papers in Europe PMC
  6. 06
    McFarland R12 papers · 2025

    Wellcome Centre for Mitochondrial Research, Newcastle University, Newcastle upon Tyne, UK.

    Papers in Europe PMC
  7. 07
    Murayama K10 papers · 2024

    Department of Metabolism, Chiba Children's Hospital, 579-1 Heta-cho, Midori-ku, Chiba, 266-0007, Japan. kmuraya@mri.biglobe.ne.jp.

    Papers in Europe PMC
  8. 08
    Compton AG9 papers · 2021

    From the Murdoch Children's Research Institute, Royal Children's Hospital and Department of Paediatrics, University of Melbourne, and alison.compton@mcri.edu.au.

    Papers in Europe PMC
  9. 09
    He L9 papers · 2020

    Wellcome Centre for Mitochondrial Research, Newcastle University, Newcastle upon Tyne, UK.

    Papers in Europe PMC
  10. 10
    Willems PH9 papers · 2016

    Department of Biochemistry, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, Nijmegen, The Netherlands Centre for Systems Biology and Bioenergetics, Radboud University Medical Center, Nijmegen, The Netherlands.

    Papers in Europe PMC

Clinical research

Is a treatment being tested?

0

interventional trials for this specific condition

No interventional trial testing a treatment matched this specific condition name on ClinicalTrials.gov (observational studies and pan-disease registries are listed separately when present).

Data as of 11 September 2026 · last trial check 11 September 2026

No matched interventional trials. This is true for 77.2% of diseases in the trials denominator (5501 of 7126). Here are the researchers publishing on it.

high confidence · 38.6th percentile (trials denominator)

Recruiting interventional trials

From the matched ClinicalTrials.gov set

No interventional trial testing a treatment was found for this specific condition name on ClinicalTrials.gov.

See who's working on it — people publishing on this disease are often the practical next contact when no trial is listed.

Other registries (secondary)

Broader net from EU CTIS, ISRCTN, and ICTRP when available — deduped against ClinicalTrials.gov IDs already counted above. Dual-model LLM relevance gates what we keep. These rows are not added to the interventional headline.

raw 2 · after dedupe 2 · already on CT.gov 0 · kept 0 · parent 0 · uncertain 2 · dropped 0 · fetched 2026-07-29

Source notes: ictrp: Error: ICTRP public search unavailable (WHO portal is SPA-only; SOAP needs partnership). Tried: https://apps.who.int/tri

No secondary-registry studies passed dual-model relevance for this condition name (after dedupe).

Uncertain / not reviewed (2)

Where to find support

Condition-specific patient organisations, when Orphanet lists them, are on the disease’s Orphanet page. We also link umbrella groups that support undiagnosed and ultra-rare families.

Orphanet entry for Isolated complex I deficiency — check Associations / patient organisations on that page.

India — NPRD

Last verified 2026-07-26

This ORPHAcode is not on our curated NPRD list (direct or Mondo-parent match). That does not decide clinical eligibility; families in India should ask a notified Centre of Excellence about current coverage.

Hand-curated for this project. ORPHAcode mappings are best-effort and may be incomplete or imprecise for umbrella categories. Parent (Mondo) matches mean the policy lists a broader category — confirm eligibility with a Centre of Excellence. Financial entitlements summarised from public policy statements and may change. This is not official government guidance.

How we counted this

Europe PMC query (preferred label + any corrected label + Orphanet and Mondo exact synonyms, stoplisted; unioned with resolved MeSH labels when available). UMLS / OMIM / NCIT cross-references are stored on the overview but are not added to the query string.

("Isolated complex I deficiency" OR "Isolated NADH-CoQ reductase deficiency" OR "Isolated NADH-coenzyme Q reductase deficiency" OR "Isolated NADH-ubiquinone reductase deficiency" OR "Isolated mitochondrial respiratory chain complex I deficiency" OR "NADH coenzyme Q reductase deficiency" OR "complex 1 mitochondrial respiratory chain deficiency" OR "mitochondrial respiratory chain complex I deficiency") OR ("SLC35G2" OR "SLC35G2 syndrome" OR "SLC35G2-related")

Run this search on Europe PMC

ClinicalTrials.gov query (quoted phrases + MeSH via query.cond, plus recall-expansion terms when used):

"Isolated complex I deficiency" OR "Isolated NADH-CoQ reductase deficiency" OR "Isolated NADH-coenzyme Q reductase deficiency" OR "Isolated NADH-ubiquinone reductase deficiency" OR "Isolated mitochondrial respiratory chain complex I deficiency" OR "NADH coenzyme Q reductase deficiency" OR "complex 1 mitochondrial respiratory chain deficiency" OR "mitochondrial respiratory chain complex I deficiency"

Study-type breakdown: 0 interventional · 0 observational · 0 expanded access. Only interventional studies enter the trial headline.

Query health: ok — strategies attempted: phrase; with hits: phrase

Run this search on ClinicalTrials.gov

Confidence reasoning

  • Preferred label is multi-word and distinctive
  • No synonyms dropped by stoplist
  • No label/synonym collisions with other diseases in this corpus

Ingested 2026-07-26T20:40:26.296Z