Maple syrup urine disease (MSUD) is an inherited metabolic disorder in which the body cannot break down certain protein building blocks (the branched-chain amino acids leucine, isoleucine, and valine). They build up quickly and can cause serious brain injury within days if untreated, so it is named for the sweet, maple-syrup smell it can give a baby’s urine, and it is treated as a newborn emergency.
What causes MSUD
MSUD is caused by changes in the genes that make the enzyme complex needed to process branched-chain amino acids. It is inherited in an autosomal recessive pattern.
How newborn screening detects MSUD
MSUD is screened for in all U.S. states by measuring branched-chain amino acid levels in the dried blood spot. Because harm can occur rapidly, an out-of-range result is urgent and confirmed promptly with specialist evaluation.
How MSUD is managed
Treatment is a carefully controlled, low branched-chain amino acid diet with a special medical formula, started as early as possible, plus prompt management during illness when levels can spike. Early, consistent treatment supports healthy development.
Related conditions beyond the standard panel
Standard newborn screening covers several amino acid disorders, including MSUD and PKU, but many rarer amino acid, urea cycle, and organic acid disorders vary by state and are not universally screened. Genomic screening can assess the genes linked to a much broader set of metabolic conditions than any biochemical panel.
How genomic screening fits in
State screening catches MSUD well. Fore Genomics’ at-home cheek-swab screen looks at the genes tied to more than 1,000 clinically actionable childhood conditions, including metabolic disorders beyond the standard panel, sequenced in CLIA-certified and CAP-accredited labs with genetic counselor support. See what we screen for or start screening.
Frequently asked questions
Is MSUD on every state’s newborn screening panel?
Yes. MSUD is screened for in all U.S. states.
Why is MSUD treated so urgently?
Branched-chain amino acids can rise quickly after birth and cause brain injury, so early diagnosis and a specialized diet are essential.
Medically reviewed by Fore’s Clinical Team. This article is for general educational purposes and is not medical advice. Sources: HRSA Newborn Screening; National Organization for Rare Disorders (NORD).