The majority of children with intermediate MSUD are diagnosed between the ages of 5 months and 7 years. Symptoms associated with classic MSUD also appear in intermediate MSUD. Intermittent MSUD
Contrary to classic and intermediate MSUD, intermittent MSUD individuals will have normal growth and intellectual development. Symptoms of lethargy and characterized odor of maple syrup will occur when the individual experiences stress, does not eat, or develops an infection. Metabolic crisis leading to seizures, coma, and brain damage is still a possibility. Thiamine-response MSUD
Symptoms associated with thiamine-response MSUD are similar to intermediate MSUD. Newborns rarely present with symptoms. Later onset
The symptoms of MSUD may also present later depending on the severity of the disease. Untreated in older individuals, and during times of metabolic crisis, symptoms of the condition include uncharacteristically inappropriate, extreme or erratic behaviour and moods, hallucinations, lack of appetite, weight loss, anemia, diarrhea, vomiting, dehydration, lethargy, oscillating hypertonia and hypotonia, ataxia, seizures, hypoglycaemia, ketoacidosis, opisthotonus, pancreatitis, rapid neurological decline, and coma. Death from cerebral edema will likely occur if there is no treatment. Additionally, MSUD patients experience an abnormal course of diseases in simple infections that can lead to permanent damage. Causes
Mutations in the following genes cause maple syrup urine disease:

BCKDHA (OMIM: 608348)
BCKDHB (OMIM: 248611)
DBT (OMIM: 248610)
DLD (OMIM: 238331)These four genes produce proteins that work together as the branched-chain alpha-keto acid dehydrogenase complex. The complex is essential for breaking down the amino acids leucine, isoleucine, and valine.
Maple syrup urine disease (MSUD) is an autosomal recessive metabolic disorder affecting branched-chain amino acids. It is one type of organic acidemia. The condition gets its name from the distinctive sweet odor of affected infants urine and earwax, particularly prior to diagnosis and during times of acute illness. Signs and symptoms
The disease is named for the presence of sweet-smelling urine, similar to maple syrup, when the person goes into metabolic crisis. The smell is also detected in ear wax of an affected individual during metabolic crisis. In populations to whom maple syrup is unfamiliar, the aroma can be likened to fenugreek, and fenugreek ingestion may impart the aroma to urine. Symptoms of MSUD varies between patients and is greatly related to the amount of residual enzyme activity. Classic MSUD
Infants with classic MSUD will display subtle symptoms within the first 24–48 hours. Subtle symptoms include poor feeding, either bottle or breast, lethargy, and irritability. The infant will then experience increased focal neurologic signs. These neurologic signs include athetoid, hypertonia, spasticity, and opisthotonus that lead to convulsions and coma. If MSUD is left untreated, central neurologic function and respiratory failure will occur and lead to death. Although MSUD can be stabilized, there are still threats of metabolic decompensation and loss of bone mass that can lead to osteoporosis, pancreatitis, and intracranial hypertension. Additional signs and symptoms that can be associated with classic MSUD include intellectual limitation and behavioral issues. Intermediate MSUD
Intermediate MSUD has greater levels of residual enzyme activity than classic MSUD.