Maple Syrup Urine Disease (MSUD) is a disorder of protein metabolism that leads to neurological differences. It is an exciting time where people diagnosed with MSUD are living longer. The investigators want to learn about how adults with MSUD think, feel, and live. The purpose of this research study is to 1) look at thinking skills, behavior skills, life skills, and quality of life in adults with MSUD and 2) measure how medical and personal factors impact these areas. The results of the study will be used to learn how to best help adults with MSUD and how to prepare for their success. In this study, the participants will answer questions on thinking, life skills, behavior skills, and quality of life. These questions will be completed on the internet. The participants will have a formal testing of their thinking and behavior completed virtually. The participants may also have a 1-2-hour telephone conversation about their life. All tests will occur virtually at home. The investigators will send the participants a letter with the results of thinking and behavior tests.

Inclusion Criteria for Index Subjects:

• Males or females 21 years and older
• Diagnosis of MSUD
• Ability to communicate verbally or using augmentative communication effectively to participate in appropriate neurocognitive testing

Inclusion Criteria for Comparison Subjects:

• Males or females 21 years and older
• Sibling or acquaintance of index subject
• Ability to communicate verbally or using augmentative communication effectively to participate in appropriate neurocognitive testing

Exclusion Criteria for all subjects:

• Inability to communicate verbally or using augmentative communication effectively to participate in appropriate neurocognitive testing
• Subjects or guardians or who, in the opinion of the Investigator, may be non-compliant with study schedules or procedures.
• Subjects or guardians who do not have internet access
• Subjects who do not speak English as a primary language

The study population will include 25 adults with MSUD and 25 age-matched adults for the comparison group.

IPD will not be shared.