Gout, with a section on ocular disease in the gouty

by Llewellyn J. Llewellyn

The exact origin of creatine and creatinine is still obscure. All we know is that they are, in the main, the outcome of chemical processes in the tissues, viz., products of endogenous metabolism. Also of the creatine and creatinine present in food a moiety may appear as creatine in the urine.

Creatinine occurs in the urine of adults, and is practically independent of the protein intake. The amount excreted varies with the size, and not with the weight of the body. In other words, it varies with the volume or mass of the voluntary muscles, which structures have the highest content of creatinine and creatine. MacLeod, discussing this relationship, tells us that, “in the muscular atrophies creatine excretion is distinctly below normal.” It must, he adds, be the “mass of the muscles rather than their activities that is the determining factor, for the creatine excretion does not become increased by muscular exercises.” Otto Folin, discussing the clinical application of pathological chemistry, observes, “Nothing definite is as yet known concerning the creatinine output in abnormal metabolism, except that in fevers and other diseases there is an increase, sometimes a very large increase.” But this much we do know that creatine, after ingestion, is almost quantitatively excreted in the urine. Creatine, in considerable amount, is a normal constituent of children’s urine, but in normal adults hardly a trace occurs, though in some diseases it is met with even in their case. In boys it gradually dwindles and disappears at about seven years of age. On the contrary, in girls creatine is excreted until puberty. Subsequently, its presence in the urine is intermittent, its incidence confined to the menstrual cycles, the period of pregnancy, and for some days after parturition.

From our point of view, the most interesting of the above revelations is the fact that the largest percentage amount of creatine and creatinine is located in the muscular tissues. On this point we cannot do better than quote the following words of Otto Folin:—

“It is to be noted that we are as yet entirely ignorant of the origin and significance of the creatine which is so abundant in muscles, and it is scarcely to be doubted that fundamentally important metabolism problems somehow are connected with the muscle creatine and urinary creatinine, but these are as yet problems of normal metabolism, and it is too early to say whether, or in what way, light may be thrown on clinical problems by studies of these products. The fact that the muscles of mammals, including man, contain 0·3-0·4 per cent. of creatine, and only traces of the chief nitrogenous waste product urea, constitutes to my mind strong presumptive evidence that creatine serves some important function, and it is quite conceivable that metabolism diseases of one kind or another may be associated with this curious substance, but investigations rather than hypotheses are needed in the study of such obscure problems.”

Inborn Errors of Metabolism

Apart from its intrinsic fascination, the tracing out of analogies, clinical or pathological, between diseases apparently diverse has often proved a fruitful source of enlightenment, for the natural history of disease is such that one disorder trenches upon the clinical territory of another, symptoms overlap and similarity if not community of origin is revealed.

Few will gainsay that gouty individuals are the victims of some inborn defect or eccentricity of metabolism, and instinctively the thought arises, are there no other disorders of like character? Immediately we bethink ourselves of alkaptonuria, cystinuria and pentosuria. Sir Archibald Garrod, as we know, classed these disorders as “chemical malformation” of hereditary origin. In other words, all are the outcome of an abnormality in intermediary metabolism.

In alkaptonuria the metabolic warp concerns the aromatic groups, in cystinuria the sulphur-containing radicles of the protein molecule. On the other hand, in pentosuria the origin of the endogenous pentose is variously ascribed to the nucleo-protein of the cell nuclei or to galactose. Lastly, in gout it is in the metabolism of nucleo-protein, or rather of the nucleic acids of the cell nuclei that the flaw resides.

We see, therefore, that Langdon Brown, discussing gout, is well justified in observing that, “We may look upon a person who is readily poisoned by purins in the same light as the person who has cystinuria, alkaptonuria, or pentosuria, i.e., they all lack a link in the chain of protein katabolism, so that intermediate products appear in the urine instead of the usual end-products.” In other words, they all display a pathological kinship, viz., in that they are all due to inborn errors of metabolism.

Certain broad clinical resemblances also obtain. All members of the group, including gout, display hereditary tendencies. All occur much more often in males than in females. They all alike tend to persist through life. Lastly, their distinctive chemical products, including uric acid, are all apparently of low toxicity.