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A newborn becomes lethargic at day 3-5 of life with poor feeding and a sweet maple syrup odor. Amino acids show elevated leucine, isoleucine, and valine.
AR; BCKDHA, BCKDHB, DBT (branched-chain ketoacid dehydrogenase complex)
- Branched-chain amino acid accumulation (leucine, isoleucine, valine)
- Maple syrup odor (urine, cerumen)
- Acute encephalopathy during metabolic crises
- On RUSP
- On RUSP: flagged by elevated leucine (and isoleucine/valine) on newborn screening
- Plasma amino acids show elevated branched-chain amino acids; presence of alloisoleucine is the specific marker for MSUD
- Confirmation: biallelic variants in BCKDHA, BCKDHB, or DBT; branched-chain ketoacid dehydrogenase enzyme assay when needed
- BCAA-restricted diet, emergency protocol during illness, liver transplant curative
ILV are the three branched-chain amino acids that accumulate: Isoleucine, Leucine, Valine. Plasma leucine is the most elevated, with a ratio of leucine:valine:isoleucine of approximately 4:2:1.
MSUD = Mennonite: classic MSUD is particularly common in Old Order Mennonite communities.
Sweet urine odor: the maple syrup smell in urine and cerumen is caused by branched-chain ketoacids. Thiamine (B1) supplementation may help in responsive forms.