Beriberi is caused by a deficiency of thiamine in the diet.
severeberiberi causes an
increase in pyruvate concentrations in blood and urine. explainthis
observation.

Thiamine pyrophosphate  (derived from vitamin B1) is a coenzyme required for the activity of pyruvate dehydrogenase enzyme complex.

Explanation:

Pyruvate is the end product of glycolysis. During aerobic cellular respiration, pyruvate is oxidatively decarboxylated into acetyl CoA which in turn enters the Kreb's cycle. Oxidative decarboxylation of pyruvate is carried out by enzyme complex pyruvate dehydrogenase (PDH). The first step is simple decarboxylation and is catalyzed by pyruvate decarboxylase of the PDH complex.

The enzyme pyruvate decarboxylase and has a tightly bound coenzyme, thiamine pyrophosphate. Thiamine pyrophosphate is derived from vitamin B1. Lack of vitamin B1 in the human diet leads to beriberi that is characterized by an increased concentration of pyruvate in blood urine since oxidative decarboxylation cannot occur due to lack of the coenzyme thiamine pyrophosphate.