What's maple syrup urine disease?

A genetic disease: Infants with msud lack an enzyme to break down Amino Acids (proteins) in their diet, so the acids accumulate in their blood and tissues and become toxic, causing sweet-smelling urine, ear wax, etc-hence the name-but also brain damage. Each parent contributes one gene for this, so the parents are usually carriers. It is very rare (1:180, 000 births) and screened for in the blood test after birth.