Science Explains The Rare Urine Disease That Turns Your Pee To 'Syrup'

The ability of the body to produce and pass urine is an often overlooked, yet critical component of your everyday health Not only does urine contain excess fluids and wastes that need to be removed, but different urine colors can reveal secrets about your health, too. Any pain, changes in frequency, and urgency are all additional examples of symptoms that can require a checkup. Urine can also have unusual odors, with maple syrup–like pee a rare, yet serious possibility. Aptly named maple syrup urine disease (MSUD), this genetic condition can cause pee to smell sweet like syrup, and it can lead to severe health complications (and even death) if left untreated.

MSUD is a type of inherited metabolic condition where genetic mutations prevent your body from producing essential enzymes needed to metabolize certain amino acids from your food. For MSUD to develop, each parent must carry the mutated gene. It is therefore not possible to prevent MSUD development in people who are born with BCKDHA, BCKDHB, and DBT mutations.

MSUD is either identified in babies who are born with this condition, or in children up to 7 years old. It's so rare that an estimated 1 in 185,000 infants are affected worldwide, per Medline Plus. MSUD can be broken down into four subtypes: classic, intermediate, intermittent, and thiamine-responsive. Classic MSUD is the most common — as well as the most severe — and the signs and symptoms typically develop in babies 2 to 3 days after they're born. No matter the type of MSUD or the age of the patient, it's critical to be able to identify the key signs and to seek emergency medical care right away.

When the body cannot metabolize the amino acids associated with MSUD, they build up in the body and create sweet-smelling excrements and secretions. Consequently, this can lead to irreparable damage in the brain as well as other major organs. 

Despite its name, there are other signs of MSUD aside from urine. It can even make sweat and earwax smell sweet like maple syrup, too. Other common symptoms include appetite loss, weakness, and irritability. Collectively, these can help a doctor diagnose MSUD, and they may then follow up with genetic testing and blood tests.

Unfortunately, MSUD symptoms can quickly evolve into a metabolic crisis. This is a life-threatening event that can cause an affected person to experience sudden vomiting, muscle spasms, seizures, convulsions, and even coma. Such signs require emergency hospitalization. Some children with MSUD may also develop paralysis. Due to the significant complications associated with this genetic condition, MSUD is a part of standard newborn screenings in most states.

While diagnosed during infancy or early childhood, MSUD is a lifelong condition that must be managed throughout adulthood. Without proper diagnosis and ongoing management, it can also lead to significant physical and development complications. Among some of these complications are neurodevelopmental disorders, chronic headaches, brain damage, pancreatitis, and osteoporosis. MSUD can also be deadly in the case of a metabolic crisis or severe infection.

Currently, the only possible cure for MSUD is a liver transplant, although this is rare because of a lack of donors and the high costs associated with the procedure. There are numerous ways the liver functions in the human body, with enzyme production among them. Thus, with a new liver, your body can get the enzymes needed to help metabolize the amino acids that MSUD causes to build up. Aside from accessibility issues, a liver transplant isn't right for everyone, and it carries its own risk of complications.

Without a liver transplant, MSUD can be managed with a protein-restricted diet to help prevent life-threatening metabolic crises. This requires a careful balance between reducing branched-chain amino acids while ensuring nutritional needs are met to help support healthy growth and development. In the case of symptoms that are not resolved with dietary measures, a doctor may recommend blood filtering treatments to remove excess amino acids from the body directly.