A Phase 1/2 interventional study of KRRO-121 and Placebo in Urea Cycle Disorders, Inborn, Urea Cycle Disorders and Ornithine Transcarbamylase (OTC) Deficiency, sponsored by Korro Bio, Inc.. Recruiting at 1 site in Australia. Open to participants aged 18 Years to 65 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-10-08.
Sponsored by Korro Bio, Inc. · Phase 1/2, Interventional, and Treatment
Phase 1/2 Study of KRRO-121 is a randomized, placebo-controlled study in Healthy Volunteers (Phase 1 SAD and MAD) and Study Participants with Urea Cycle Disorders (Phase 2). The primary objective of the study is to evaluate the safety of KRRO-121.
KRRO-121 is a GalNAc-conjugated RNA editing oligonucleotide in development for the potential treatment of hyperammonemia in patients with UCDs. Utilizing Korro's proprietary OPERA® platform, KRRO-121 is designed to generate a stabilized, de novo glutamine synthetase (GS) protein, a critical enzyme involved in ammonia clearance. This synthetic rescue approach is designed to augment ammonia clearance in hyperammonemia-driven diseases such as UCDs. Korro's preclinical data support the potential for KRRO-121 to be a UCD treatment that may control ammonia levels independent of any mutational background (pan-UCD).
The purpose of this first-in-human (FIH) study is to determine the safety and tolerability of escalating doses of KRRO-121, to evaluate the pharmacokinetics of KRRO-121, and to assess the effect of KRRO-121 in healthy volunteers and in study participants with UCD. The study name is ANCHOR: AssessmeNt of Control of Hyperammonemia through Oligonucleotide-based RNA editing
66 studies on the registry are indexed under Urea Cycle Disorders, Inborn; 14 are open to participants now.
This study's planned enrollment of 30 is above the median of 17 across 39 interventional studies indexed under Urea Cycle Disorders, Inborn.
Browse Urea Cycle Disorders, Inborn studies →Korro Bio, Inc. is the lead sponsor of 2 studies on the registry; 1 is open to participants now.
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Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
ECG (electrocardiogram)
A recording of the heart’s electrical activity, taken with stickers on the chest, arms and legs. It takes a few minutes and does not hurt.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Childbearing potential
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Clinically significant
Judged by the study doctor to matter for your health or for the study. It is a doctor’s decision, so ask the study team if you are unsure whether something counts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
KRRO-121 is a GalNAc-conjugated RNA-editing oligonucleotide that recruits endogenous hepatic ADAR to edit mRNA, producing a de novo glutamine synthetase (GS) protein resistant to feedback-driven proteasomal degradation. By stabilizing hepatic GS, KRRO-121 augments ammonia clearance capacity independently of the underlying urea cycle enzyme defect.
Drug: KRRO-121
Placebo
Drug: Placebo
KRRO-121, subcutaneous injection
Placebo, subcutaneous injection
Incidence of dose limiting toxicities (DLT) (Safety and Tolerability)
General toxicity: Any Grade 3 or higher adverse event (AE) per Common Terminology Criteria for Adverse Events (CTCAE); Serious adverse events: Any serious adverse event (SAE) assessed as related or possibly related to KRRO-121.
Time frame: Day 1 through 14 days post-dose
Frequency and severity of treatment-emergent adverse events (TEAEs; per Common Terminology Criteria for Adverse Events [CTCAE]) (Safety and Tolerability)
Any adverse event (AE) per Common Terminology Criteria for Adverse Events (CTCAE),
Time frame: Day 1 through Day 50
Maximum blood concentration (Cmax)
Maximum blood concentration (Cmax) of KRRO-121
Time frame: Day 1 to Day 50
Plan to share: Undecided
No publications or documents are linked to this record.
Started Sep 2026 (actual). Primary completion is estimated for Aug 2027, 11 months after the start.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
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Urea Cycle Disorders, Inborn →
Korro Bio, Inc.