From OMIM
The major clinical features of maple syrup urine disease (MSUD) are mental and physical retardation, feeding problems, and a maple syrup odor to the urine. The keto acids of the branched-chain amino acids (BCAA) are present in the urine, resulting from a block in oxidative decarboxylation. There are 5 clinical subtypes of MSUD based on clinical presentation and biochemical response to thiamine administration: the classic neonatal severe form, an intermediate form, an intermittent form, a thiamine-responsive form, and an E3-deficient with lactic acidosis form (DLDD; 246900). All of these subtypes can be caused by mutation in the BCKDHA, BCKDHB, or DBT gene, except for the E3-deficient form, which is caused only by mutation in the DLD gene (Chuang and Shih, 2001). The classic form, which comprises 75% of MSUD patients, is manifested within the first 2 weeks of life with poor feeding, lethargy, seizures, coma, and death if untreated. Intermediate MSUD is associated with elevated BCAAs and BCKA, with progressive mental retardation and developmental delay without a history of catastrophic illness. The diagnosis is usually delayed for many months. An intermittent form of MSUD may have normal levels of BCAAs, normal intelligence and development until a stress, e.g., infection, precipitates decompensation with ketoacidosis and neurologic symptoms, which are usually reversed with dietary treatment. Thiamine-responsive MSUD is similar to the intermediate phenotype but responds to pharmacologic doses of thiamine with normalization of BCAAs. The E3-deficient MSUD is caused by defects in the dehydrogenase (E3) component of the BCKAD complex that is common to the pyruvate and alpha-ketoglutarate dehydrogenase complexes. Patients with E3 deficiency have dysfunction of all 3 enzyme complexes, and patients usually die in infancy with severe lactic acidosis (summary by Chuang et al., 1995). Genetic Heterogeneity of Maple Syrup Urine Disease MSUD1B (620698) is caused by mutation in the BCKDHB gene (248611) on chromosome 6q14, and MSUD2 (620699) is caused by mutation in the DBT gene (248610) on chromosome 1p21. Mutation in the E3 component of the BCKDC complex, DLD (238331), on chromosome 7q31, causes an overlapping but more severe phenotype known as dihydrolipoamide dehydrogenase deficiency (DLDD; 246900). DLDD is sometimes referred to as MSUD3. See also a mild variant of MSUD (MSUDMV; 615135), caused by mutation in the regulatory gene PPM1K (611065).  http://www.omim.org/entry/248600

From MedlinePlus Genetics
Maple syrup urine disease is an inherited disorder in which the body is unable to process certain protein building blocks (amino acids) properly. The condition gets its name from the distinctive sweet odor of affected infants' urine. It is also characterized by poor feeding, vomiting, lack of energy (lethargy), abnormal movements, and delayed development. If untreated, maple syrup urine disease can lead to seizures, coma, and death.

Maple syrup urine disease is often classified by its pattern of signs and symptoms. The most common and severe form of the disease is the classic type, which becomes apparent soon after birth. Variant forms of the disorder become apparent later in infancy or childhood and are typically milder, but they still lead to delayed development and other health problems if not treated.  https://medlineplus.gov/genetics/condition/maple-syrup-urine-disease