This is a non-interventional, observational, global, multicenter, study describing participant characteristics, clinical outcomes, and event rates in participants with propionic acidemia (PA).

Data will be abstracted through medical record review ensuring inclusion only of data from participants meeting all the inclusion criteria and none of the censoring criteria. Data will be collected retrospectively from study sites, including medical clinics, hospitals and academic medical centers.

Inclusion Criteria:

Participants' medical records are eligible for abstraction only if all of the following criteria apply:

• Confirmed diagnosis of PA based on diagnosis by molecular genetic testing (propionyl-CoA carboxylase subunitα[PCCA] and/or propionyl-CoA carboxylase subunitβ[PCCB] mutations).
• Participant provided informed consent (and assent, as applicable).
• Medical records with sufficient data to support medical encounter for CEC adjudication (MEA adjudication) must be available dating back to birth or 01 January 2015, whichever occurs later. Participants born prior to 2015 will require additional information to confirm eligibility.
• Experienced at least one MDE in the 24 months preceding the Index Date or experienced at least 3 MDEs within any one 12-month retrospective review period (based on Index Date) dating back to birth or 01 January 2015, whichever occurs later.
• Must have a confirmed age (months) of disease onset (early or late, where early is defined as the neonatal period).
• Participants who meet any of the censoring criteria listed below may be enrolled into the study if they have a minimum of 2 years of data available for abstraction prior to meeting the censoring criteria and they meet all inclusion criteria based on the data available for abstraction.

Censoring Criteria:

Participants medical records meeting the following censoring criterion will not be abstracted:

• Participation in a clinical study of any investigational agent.
• Received gene therapy treatment
• Confirmed organ transplantation
• Investigator is no longer able to obtain relevant clinical information of the participant.
• Death

Exclusion Criteria:

Participant's medical records will not be eligible for abstraction if the participant meets the following exclusion criteria:

- Participation (prior or ongoing) in clinical study mRNA-3927-P101 (NCT04159103) or mRNA-3927-P101-EXT (NCT05130437).

Individuals of a minimum age of 2 years with confirmed diagnosis of PA.