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.

    94/324 (page 84)
    84 aminoacid metabolism: 2 even among such homozygotes considerable variation in the relative proportions of the different aminoacids excreted from case to case may be found, and analysis of this variation has revealed further complexities in the genetical situation (28). A convenient index of this variation in pattern of excretion is the ratio of the quantity of lysine to the quantity of arginine in urine samples from different homozygous individuals. Values for this ratio as high as 4-2 and as low as 0-8 may occur in different homozygotes and these differences are larger than can be reasonable attributed to experimental error. Furthermore, the variation in the lysine/arginine ratios are very much greater among the'recessive homozygotes than among the incompletely récessives. This difference in variance is highly significant. On the other hand, the mean value for the ratio among the recessive homozygotes is not significantly different from that for the incompletely recessive ones. In the recessive group of homozygotes affected pairs of sibs closely resemble one another in the lysine/arginine excretion ratio, a sib-sib correlation coefficient of the order of 0-90 being found. In the incompletely recessive homozygotes, on the other hand, no sib-sib correlation is demon¬ strable. All this suggests that the large variation in the pattern of excretion of the recessive group of homozygotes is to a great extent genetical in origin. It seems probable that this group is heterogenous and consists of several distinct conditions caused by separate recessive genes. The affected individuals would either be homo¬ zygous for one of these genes or heterozygous for two of them. Whether or not the several genes causing 'recessive cystinuria' and the gene causing the 'incompletely recessive' condition are alleles or at different chromosomal loci remains to be discovered. Calculus formation Stone formation is a fairly frequent occurrence among individuals homozygous for one or other of the genes causing cystinuria. Prob¬ ably more than 65 per cent of such individuals develop calculi at some time in their Uves and in such people stone formation is very often recurrent. The majority of them form their first stone before the age of thirty and an appreciable fraction of these do so in infancy and childhood. Thus, although cystine calculi may account for no more than 1 per cent of all renal calculi encountered, they probably form a very much larger proportion of all calcuH occurring in child¬ hood. The exact proportion has, however, not yet been estimated.