Erythrocyte transketolase has been measured in normal controls and non-alcoholic patients not at risk from nutritional deficiency and without signs of brain damage. The enzyme activity declines steadily with age over a range from 18 to 90 years with a statistically significant fall of 25over this period. Since this decline is apparent whether or not thiamin diphosphate is addedin vitroto activate the apoenzyme, the activation ratios are independent of the age effect. The decline is seen in both sexes in patients and normal subjects. It is concluded that the reliability of the specific transketolase activity as an indicator of marginal thiamin deficiency will be improved if the results are expressed as a percentage of the mean normal value corrected for age with values less than 60of the age adjusted mean taken to indicate possible deficiency.
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