Maple Syrup Urine Disease
Maple syrup disease (MSUD) is due to a deficiency of branch chain a-keto acid dehydrogenase, a multienzyme complex associated with inner membranes of mitochondria generally patients have absence or reduced levels of a-keto acid decarboxylase subunit of the complex which catalyzes the oxidative decarboxylation of the a- keto acids derived from the deamination of leucine ,isoleucine and valine. MSUD is inherited as an autosomal recessive trait that affects 1:200,000infants worldwide. it occurs with a much higher frequency in people of French -Canadian ancestry, Ashkenazi Jews and old order Mennonite population of Pennsylvania.
There are five clinical subtypes of MSUD. the most common and severe from of the disease is the classic from which becomes apparent in the first week after birth and the enzyme activity is less than 2% of normal. some forms like intermittent branch chain ketonuria have impaired but distinct capacity to breakdown branch chain amino acids. another variant is a thiamine responsive from that express a mutant enzyme with reduced affinity for thiamine pyrophosphate (TPP) the less severe forms respond to dietary therapy and symptoms develop later in life.
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