Study of YOLT-203 in Children and Adults With Primary Hyperoxaluria Type 1 (PH1)

Inclusion Criteria

* You are 6 years old or older.
* You have been diagnosed with PH1 (primary hyperoxaluria type 1) through genetic testing.
* Urine tests show that your oxalate levels are not within certain limits (based on at least two 24-hour urine collections).
* If you take vitamin B6, your dose has been stable for at least 3 months, and you are willing to keep it the same during the study.
* You (and/or your parent or legal guardian, if you are under 18) understand the study and agree to follow all study requirements, including signing a consent form.

Exclusion Criteria

* You have signs that oxalate has affected parts of your body outside the kidneys.
* Your liver blood tests are not within certain limits.
* You have certain abnormal blood clotting results (unless controlled with medication like warfarin).
* You have HIV, or active or chronic hepatitis C.
* You are pregnant, planning to become pregnant, or breastfeeding.
* You are not willing to use birth control during the study and for 6 months after (if applicable).
* You are unable to limit alcohol intake to no more than about 2 drinks per day.
* You have had alcohol or drug abuse in the past year.
* You are unable to follow standard treatments for PH1 (such as drinking plenty of fluids, taking prescribed medications like potassium citrate, or following dietary advice).