Maple Syrup Urine Disease, Type 1B
OMIM number: 620698
Comments closing date: 09/02/2026
MSUD is an inherited metabolic condition caused by a problem with a group of proteins that normally help the body break down the amino acids leucine, isoleucine and valine. In MSUD 1B, mutations in the gene BCKDHB lead to dysfunction of the BCKD complex. Because of this, those amino acids, and related toxic by-products, build up in the body. This can lead early on to symptoms such as poor feeding, lack of energy, irritability, sleepiness, and in many infants a distinctive “maple-syrup” smell in urine. If not treated early, this toxic buildup can cause serious problems including brain damage, delayed development, seizures, coma or even death. MSUD 1B is inherited in an autosomal recessive pattern. There is no cure, but early detection plus careful lifelong treatment can greatly reduce the risks. Treatment involves a strictly controlled diet that limits the amounts of the problematic amino acids, specialised medical foods, and close monitoring of blood levels and health. In some cases a healthy transplanted liver can restore the missing enzyme activity. With early diagnosis and good ongoing management, many individuals with MSUD can lead comparatively normal lives, although frequent monitoring and lifelong dietary attention are
typically needed.
