Maple Syrup Urine Disease

By: John and Amber

Introduction: What is Maple Syrup Urine Disease?

Maple Syrup Urine Disease or branched-chain ketoaciduria is an autosomal recessive metabolic disorder affecting branched-chain amino acids. It is a type of organic acidemia. It makes the urine of infants smell like maple syrup. 1 in every 180,000 infants worldwide are affected, and there is a larger percentage in Mennonite and Amish communities. The condition is named because the smell of an affected infant's urine is sweet like maple syrup. It does not affect adults whatsoever if they are treated properly. It is passed down when two people have the recessive trait that causes MSUD.

Diagnosis and Symptoms

MSUD is caused by the back-up of toxic amino acids like leucine, isoleucine, and valine. The deficiency of the branched chain alpha-keto acid dehydrogenase complex (BCAKADH) makes the toxins build up in the blood and urine.
The symptoms of the disease can be fatal to infants if left untreated. The symptoms include sweet smelling urine, poor feeding, vomiting, dehydration, lethargy, hypotonia, seizures, ketoacidosis, pancreatitis, and coma and neurological decline. The child can become severely brain damaged from MSUD.


Pattern of Classification

The disease is classified by the signs, symptoms, and genetic cause. The most well known classification is the form that appears right after birth. There are 5 types of classification: classic severe, intermediate, intermittent, Thiamine-responsive, and E3 Deficient with lactic acidosis.


Kids with it have to have careful blood monitoring and have to rely on a dietitian. They need minimal levels of leucine, isoleucine, and valine. The food is synthesized with proteins to help the affected live healthy lives. The diet is rigorous and must be adhered every day.

MSUD on a Molecular Level

MSUD is a genetic mutation in the BCKADH(branched chain keto acid dehydrogenase E1, alpha polypeptide), BCKDHB(branched chain keto acid dehydrogenase E1, beta polypeptide), DBT(dihydrolipoamide branched chain transacylase E2), and DLD(dihydrolipoamide dehydrogenase) genes. When mutated, the BCKADH gene cannot break down leucine, isoleucine, and valine. When this happens, these amino acids and their byproducts compile in the brain. This is extremely toxic to cells in the brain, and it causes seizures, developmental disorders, and almost anything else caused by MSUD. When mutated, all of the other genes affected also cannot break down leucine, isoleucine, and valine.