THE ETIOLOGY OF PERNICIOUS ANEMIA AND
RELATED MACROCYTIC ANEMIAS*
By W. B. CASTLE, F.A.C.P., Boston, Massachusetts
DURING the past five years the problem of the etiology of pernicious
anemia and other macrocytic anemias responding to liver extract has been
investigated at the Thorndike Memorial Laboratory, Boston City Hospital.
At various times Dr. Wilmot C. Townsend, Dr. Clark W. Heath, Dr. Maurice B. Strauss and myself have been engaged in this study. Last year, in
collaboration with Dr. C. P. Rhoads of the Rockefeller Hospital, the macrocytic anemia of sprue in Puerto Rico was studied under the auspices of the
Rockefeller Foundation. Recently Dr. Strauss has investigated the mechanism of the pernicious anemia of pregnancy.
The technic first employed was the incubation of various preparations of
normal human gastric juice with beef muscle and the administration of the
suitably prepared incubated material to cases of pernicious anemia. The
presence or absence of hematopoietic effects has been determined by the appearance or non-appearance respectively of significant reticulocyte increases
during successive ten-day periods of daily administration of the incubation
mixtures. Sufficient experiments of this type have previously been reported
to demonstrate that Addisonian pernicious anemia is a deficiency disease conditioned by the lack of a specific intrinsic factor, present in normal human
gastric juice and absent in that of cases of pernicious anemia in relapse.1' 2» 8»4
In the normal individual the function of this intrinsic factor of the gastric
juice is to interact with an extrinsic factor in the food to produce specific
hematopoietic effects (demonstrable in pernicious anemia). Alone, neither
normal human gastric juice nor beef muscle has yielded significant hematopoietic responses in pernicious anemia. However, the daily administration
of mixtures of beef muscle and gastric juice to suitable patients with pernicious anemia invariably produced reticulocyte increases and when prolonged over several weeks was sufficient to bring the blood and the clinical
condition essentially to normal. The interaction of these two factors may,
therefore, be regarded as preventive of the development of pernicious anemia
in the normal individual. Conversely, the failure of this reaction to take
place may be expected to lead to the development of pernicious anemia.
Thus, all the patients with Addisonian pernicious anemia in relapse, who
have so far been examined, have shown an inability to carry out this essential
reaction. It is important to emphasize that these observations demonstrate
the existence of a physiological mechanism in the normal individual which
* Address delivered by Dr. W. B. Castle as recipient of the John Phillips Memorial Prize
at the Montreal Meeting of the American College of Physicians, February 6, 1933.
From the Thorndike Memorial Laboratory and the Second and Fourth (Harvard) Medical Services of the Boston Gty Hospital, and the Department of Medicine of the Harvard
Medical School.
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THE ETIOLOGY OF PERNICIOUS ANEMIA
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is absent in the patient with pernicious anemia in relapse. Both the food
and the stomach are involved in this process. On the other hand, the demonstration of the hematopoietic activity of various substances such as arsenic,
liver, kidney, brain, and even stomach preparations or the injection of milk
or gastric juice, does not necessarily establish their etiological relationship
to the disease, despite their efficiency in its treatment.
The intrinsic factor of the normal gastric juice has been defined as a heatlabile substance, not corresponding in its properties to hydrochloric acid,
pepsin, rennin, or lipase.5 Recently Dr. Strauss and I have turned our attention to the extrinsic factor, and incubation of various substances has been
carried out with normal human gastric juice. Starting with the results of
the previous observations demonstrating that the extrinsic factor of the food
has been found in the washed proteins of beef muscle precipitated at pH 6,
but not in washed casein or wheat gluten, the former of which is a relatively
complete protein,4 the work was extended to nucleoproteins and their derivatives. The results of these observations make it clear that nucleoproteins,
and nucleic acid from animal sources and from yeast, cannot react effectively
with normal human gastric juice. On the other hand, we have now shown
that the extrinsic factor is present in autolyzed yeast in approximately 20
times the concentration found in beef muscle. It is not destroyed by autoclaving for five hours at 15 pounds' pressure, which destroys vitamin Bx but
not vitamin B 2 ; and it is separable from the proteins of yeast by 80 per cent
alcohol in which it is soluble.6 In addition, the extrinsic factor is found in
rice polishings and in wheat germ. Liver extract No. 343 N.N.R., a source
of vitamin B2, may be rendered inactive in pernicious anemia by hydrolysis
with dilute sulfuric acid, a procedure that does not destroy vitamin B2. If
this hydrolyzed material is then incubated with normal human gastric juice,
it is again rendered active. In general, then, the characteristics and distribution of the extrinsic factor correspond to those of vitamin B2.
We 5 have previously pointed out that there are three possible mechanisms
by the action of one or more of which pernicious anemia may be produced,
namely, a lack of the specific intrinsic factor of the stomach, a lack of the
extrinsic factor of the diet, or a failure of absorption or utilization of the
product of the interaction of the intrinsic and extrinsic factors. These
postulates can now be extended to include other types of macrocytic anemia
and can be shown to be consistent with the supposition that vitamin B2 is the
extrinsic factor.
1. All cases of classical Addisonian pernicious anemia in relapse which
we have studied thus far, have been mainly due to the operation of the first
mechanism, a lack of the intrinsic factor in the stomach.
2. Sprue with macrocytic anemia, on the other hand, has been successfully treated by Elders7 and Ashf ord8 with diets rich in animal protein, and
hence rich in vitamin B 2 ; and more recently we 9 have had success in certain cases with yeast. Similarly Wills 10 has successfully treated tropical
macrocytic anemia with autolyzed yeast alone, and Vaughan and Hunter l l
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W. B. CASTLE
have obtained definite results with the same substance in the macrocytic
anemia of celiac disease. These results may now be explained on the basis
that in all probability the anemia was mainly due to the second mechanism
outlined above, namely, a lack of the extrinsic factor in the diet.
3. It must, however, be remembered that in certain cases of macrocytic
anemia, the third possibility, namely, defects of absorption, may be involved.
Thus, in certain cases of pernicious anemia and especially in advanced cases
of sprue, enormous doses of liver extract given by mouth may be relatively
ineffective while the usual parenteral dose gives a typical response.5 It is
possible that various factors within the body may also be involved in these
differences. It has also been pointed out that the same mechanism may not
always be active. This is best illustrated by certain cases of the pernicious
anemia of pregnancy which during pregnancy show no response to beef
muscle. After delivery, however, beef muscle produces a reticulocyte response which may be then increased by the addition of normal human gastric
juice.12*18 This we interpret as indicating a lack of the intrinsic factor in
the gastric juice during pregnancy and its partial recrudescence after parturition. The reappearance of the intrinsic factor has also been observed in
one case of pernicious anemia following the improvement induced by liver
therapy.5
It is now possible to explain why certain cases of macrocytic anemia will
respond to both liver extract and autolyzed yeast and others only to liver extract. The difference appears to depend on the presence or absence of the
intrinsic factor. In the light of this evidence it is clear that the common
factor for producing macrocytic anemia is the failure of the specific reaction
between the extrinsic and the intrinsic factors. These anemias should, then,
occur both where, on the one hand, the diet is deficient in vitamin Ba, and
on the other hand, where, although the diet is not grossly deficient, lack of
the intrinsic factor is found. Thus, sprue and the macrocytic anemias of
the tropics occur in communities or in individuals partaking of defective diets
and show gastric anacidity less commonly than is found in patients with
Addisonian pernicious anemia, who usually have more normal diet habits.
In many cases a combination of gastric defect and dietary deficiency may
exist, which would have the same result upon the specific hematopoietic reaction as a total absence of either of its components.
If the evidence be valid that the extrinsic factor of the specific hematopoietic reaction with normal htunan gastric juice is vitamin B2, a new concept
of the relation of certain vitamins to the conditions caused by their lack
would seem to be involved. The action of a vitamin in curing a deficiency
may thus be essentially dependent upon a specific process in the gastrointestinal tract; and the deficiency state not so much a deficiency in the diet as a deficiency of a reaction in the gastrointestinal tract or elsewhere in the body.
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THE ETIOLOGY OF PERNICIOUS ANEMIA
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