Maple Syrup Urine Disease (MSUD) was first described in 1954 by Menkes.

Maple Syrup Urine Disease (MSUD) is a hereditary metabolic disease with an autosomal recessive inheritance pattern.

It appears in the first few days of life and is distinguished by the onset of neurological disorders due to the lack of certain enzymes (decarboxylases), resulting in the blocking of oxidative decarboxylation (the reaction in which a substance is oxidised and a molecule of carbon dioxide liberated) of branched-chain amino acids (leucine, isoleucine and valine).

These amino acids accumulate in the body, and the presence of keto acids in the urine gives it a characteristic smell of maple syrup (hence the name MSUD) or burnt sugar.

The classic form representes 90% of cases. The enzyme activity is between 0 to 2%.

This form is distinguished by a progression to deep coma with difficulties in sucking, anorexia, vomiting and sleepiness.

The other 10% forms appear later and are atypical.

There are also &lquot;intermediate&rquot; forms with psychomotor retardation and &lquot;intermittent&rquot; forms with deep coma with lower leucine value.

This is an orphan disease with no neonatal screening.

In the general population, MSUD occurs in 1/150 000 births, but incidences rates are sometimes much higher in certain populations: 1/ 84 000 in Georgia or 1/ 700 in Amish population for example. The screening is extremely important in this population !