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Maple Syrup Urine Disease (MSUD)

MSUD is a serious inherited metabolic disorder that can lead to severe brain damage if unmanaged.1

In MSUD, the body lacks an enzyme called branched chain ketoacid dehydrogenase. This enzyme is responsible for breaking down three amino acids called leucine, isoleucine and valine. Therefore, these amino acids accumulate in the blood of patients with MSUD.1


How is MSUD diagnosed?1

MSUD is usually diagnosed from the newborn blood spot screening test which is offered to all babies approximately 5 days after birth to test for several conditions including MSUD. This involves testing a small blood sample collected from pricking of the baby’s heel. In patients with MSUD, this test will detect high levels of the amino acid leucine in the blood. However patients may develop symptoms before the test is carried out such as poor feeding, vomiting, dehydration, lethargy or seizures.

Older children with MSUD may develop symptoms later and present with developmental delay or vomiting/diarrhoea.


How is MSUD managed?

The effects of MSUD quickly become life-threatening if unmanaged and early management can prevent brain damage and learning difficulties.

MSUD is managed with a special low protein diet which includes protein substitutes, vitamin and mineral supplements and a measured amount of protein containing foods. Foods containing high amounts of protein must be avoided such as meat, fish, eggs, bread and pasta.1 The aim is to keep the blood levels of leucine, isoleucine and valine within a specific target range.2

A baby with MSUD will have a highly regulated milk (may be formula or breastmilk) intake according to specialist metabolic dietetic input in order to meet their nutritional requirements.1

Patients require regular blood tests to monitor amino acid blood levels together with regular developmental checks such as height and weight. Diet is adjusted accordingly.1

Patients and families of patients must be educated about the condition in order to identify the signs of a toxic build up of amino acids in the blood – this is called a metabolic crisis. 1 This can be triggered by a childhood illness and so it is vital that it is recognised and medically managed quickly.1 Additionally, patients will require an emergency treatment regime that differs from their usual diet/treatments during periods of illness to prevent the development of a metabolic crisis. Blood tests will likely be required together with close input of the patients’ metabolic team.1


References MSUD

1. British Inherited Metabolic Diseases Group. TEMPLE guide. MSUD. April 2020. Available from; https://www.bimdg.org.uk/store/temple//B20030_Temple_Updates_MSUD_DIGITAL_-_Final_Approved_221450_03092020.pdf (Accessed 19th Oct 2021)
2. https://metabolic.ie/patient-family-information/metabolic-conditions/maple-syrup-urine-disease-msud/ (Accessed 19th Oct 2021)