Human biochemical genetics / by H. Harris.

  • Harris, Harry, 1919-1994.
Date:
1966
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Human biochemical genetics / by H. Harris. Source: Wellcome Collection.

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    ш AMINO ACID METABOLISM: 2 ! The significance of aminoaciduria The excretion of aminoacids in unusual amounts in urine occurs in a variety of different inherited biochemical disorders (i) and very often the detection of the aminoaciduria has represented the starting-point in the investigation of such conditions. The abnormal excretion of aminoacids can result from diverse causes and frequently shows characteristic and highly specific features. Some general questions concerning the mechanism by which aminoaciduria may arise are therefore worth considering before discussing in more detail certain of the syndromes in which it has been observed. In practice (2) it is useful to classify aminoacidurias into two main groups; the 'overflow' aminoacidurias, and the 'renal' amino¬ acidurias. The 'overflow' aminoacidurias arise because there is some defect in intermediary metabolism leading to an increase in plasma level of one or more aminoacids to such a degree that the normal renal tubular reabsorptive mechanism is unable to deal with them adequately and they therefore pass in increased quantities into the urine. The 'renal' aminoacidurias are due to some defect in the processes of renal tubular reabsorption so that even at normal plasma concentrations, and hence normal concentrations in the glomerular filtrate, inefficient reabsorption of one or more amino¬ acids takes place, and so abnormal amounts are found in the urine. The particular aminoacids occurring in excess in the urine will depend in the 'overflow' type on the specific character of the disturbances in intermediary metabolism, and in the 'renal' type on the particular way in which the renal tubules are defective. It is possible of course that in certain circumstances both types of cause may operate, but in most cases the aminoaciduria appears to fall quite clearly into one or other of these two classes. Theoretically renal aminoaciduria might also be caused by active tubular secretion but so far no definite example of this has been discovered. Difl'erentiation between the tv/o general causes of aminoaciduria can usually be made from a consideration of the plasma concentra-