Sunday, 21 July 2013

Types of MSUD




Classic MSUD is the most common type of MSUD. In classic MSUD, there’s little or no enzymatic activity taking place, usually having 2% of the enzyme activity present only. Infants with classic MSUD will show symptoms within the first several days of life. Generally, they will have poor tolerance for BCAAs, so protein should be strictly restricted in their diet.



Intermediate MSUD is a variation of the classic MSUD. Those with intermediate MSUD have a higher level of enzyme activity which approximately 3-8% from normal people. They can usually tolerate a greater amount of leucine. However, when ill or fasting, the child with intermediate MSUD reacts just like a child with classic MSUD. Management is similar for the intermediate and classic types of MSUD.



Intermittent MSUD is a milder form of the disease because there is much more enzyme activity compared to the previous types of MSUD (approximately 8-15% of normal). Often the child does not have symptoms until 12 to 24 months of age, usually in response to an illness or surge in protein intake. During episodes of illness or fasting, the BCAA levels elevate, the characteristic maple syrup (or burnt sugar) odor becomes evident, and the child can go into a metabolic crisis.



Thiamine-responsive MSUD is basically just what the name implies. Giving large doses of thiamine to the thiamine-responsive child will increase the enzyme activity which breaks down leucine, isoleucine and valine. In most cases only moderate protein restriction is needed for this more rare type of MSUD.


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