MSUD is short for Maple Syrup Urine Disease. People with MSUD may have an unusual sweet smell in both the urine and sweat, which is where this name comes from. MSUD is a rare genetic condition of metabolism. In many countries, there will only be 1 baby born with MSUD for every 185,000 babies born.

MSUD varies considerably from what is called classical MSUD to milder variants of the disorder. With early diagnosis and the right medical and dietary treatment, the outcomes for individuals with MSUD can be greatly improved, compared to untreated MSUD.

When an individual has MSUD, their body is unable to properly manage a nutrient in food called protein. Protein is found in many foods but certain foods (e.g. meat, fish, chicken, nuts and eggs) have more protein than others. To be more exact, the body has problems with three parts of protein:

  • Protein is made up of ‘building blocks’ called amino acids
  • Three of these amino acids are called Leucine, Isoleucine and Valine (also known as branched chain amino acids or BCAAs)

There is an enzyme in the body called branched chain ketoacid dehydrogenase (BCKDH complex for short). In MSUD, the enzyme BCKDH does not work well or might not work at all. The main problem with this, is that it causes a build-up of Leucine, Valine and Isoleucine. This therefore necessitates a low protein diet for life.

These three amino acids compete against each other in the body. Leucine is toxic to the brain and is restricted in MSUD by reducing overall protein intake. Most people with MSUD need to take supplements of isoleucine and valine alongside the prescribed diet due to this competing factor. This helps to maintain a healthy level of these amino acids in the blood without causing harm.

Early diagnosis, combined with effective life-long dietary and medical management, can lead to good outcomes in MSUD. Depending on severity, some individuals may require life-long support in certain aspects of life. Some other individuals with early diagnosed, well-managed MSUD who haven’t suffered prolonged periods of elevated leucine, can enjoy the same expectations in life (in terms of education, employment and family life) as everybody else.

In more and more countries, a system known as nationalised newborn screening (NBS) is being introduced. This means that every baby born in these countries will be offered testing for MSUD. This allows for MSUD to be diagnosed in the early days of life, which means that more and more babies with MSUD are being diagnosed earlier and achieving these positive outcomes. Some babies may become unwell before diagnosis, but early diagnosis allows high BCAA levels to be quickly reduced, minimising the severity and risk of long-term damage.

Untreated MSUD can result in neurological impairment, intellectual implications and in some instances death. The amount of leucine, isoleucine and valine in the body is determined by measuring the amount of BCAAs in the blood. Long-term, blood BCAAs need to be kept within specific limits which are known as the target blood BCAA range. These limits are set by the medical experts working in this area. Even in individuals who were diagnosed and started dietary and medical management early in life, there can be dangers if leucine levels go too high, so it is very important that medical and dietary advice is followed at all times.