The primary objective of the study is to determine if dimethyl fumarate (DMF) causes changes in the abundance and diversity of commensal microbiota. The secondary objectives of this study are as follows: To identify if there are differences in the gut microbiota composition between patients that do or do not develop gastro intestinal (GI) adverse events (AEs), both pre- and post DMF treatment and to examine if the resolution of GI AEs in DMF treated patients is reflected in the gut microbiota.

Key Inclusion Criteria:

• Have a confirmed diagnosis of RRMS and satisfy the therapeutic indication as described in the local label.
• Female subjects of childbearing potential who are not surgically sterile must practice effective contraception according to the summary of product characteristics (SPC) during their participation in the study and be willing and able to continue contraception for 30 days after their last dose of study treatment.

Key Exclusion Criteria:

• Diagnosis of primary progressive, secondary progressive or progressive relapsing MS.
• Antibiotic treatment in the last month prior to study entry.
• Scheduled alteration of diet, including the use of probiotics.

NOTE: Other protocol defined inclusion/exclusion criteria may apply.