INTELLIGENCE
OF CHILDREN
WITH
DIABETES
MELLITUS
Marvin Ack, Ph.D., Irving Miller, B.S., and William B. Weil, Jr., M.D.
Departments of Child Psychiatry, Preventive Medicine and Pediatrics, Western Reserve University
School of Medicine and University Hospitals of Cleveland
This study was supported in part by the National Institute of Arthritis and Metabolic Diseases, Public Health Service (Grant A-1317), the Foundation for the Study of Diabetes and Related Metabolic
Dis-orders, the Cleveland Diabetes Fund, and the Lorain (Ohio) United Health Foundation.
ADDRESS: (MA.) University Hospitals of Cleveland, 2065 Adelbert Road, Cleveland 6, Ohio.
PEDIATIIICS. November 1961
I
T IS WIDELY RECOGNIZED that anunder-standing of the intelligence and the
intellectual functioning of patients with
chronic diseases plays a critical role in the
management of such illnesses as diabetes
mellitus. The life expectancy for children
with diabetes is lengthening, so their future
as adults must be thoughtfully considered.
Their productivity as adult members of
society is contingent upon the enligiltelled
management of all aspects of their disease,
and in particular the physician needs to
un-derstand the effect of diabetes on
intellec-tual functioning and intellectual potential.
Although the need has long been
recog-nized as crucial and the problem of the
intellectual functioning of persons with
diabetes mellitus has been under
investi-gation since 1922, nonetheless our
knowl-edge of the intelligence of persons with
diabetes is extremely sketchy. Results of
previous investigations are contradictory.
Many of the studies have been based on
groups of patients in which unrecognized
bias occurred as a result of the method of
patient selection. The present
communica-tion is intended to indicate some of the
inconsistencies and misconceptions tilat
exist.
The study reported here is part of a
longitudinal study of diabetes mellitus in
children designed to investigate the
rela-tionship between the duration of tile
dis-ease process and the intellectual
function-ing of these children during a period of
10 to 15 years. The results reported here
represent findings of the initial phase of
the larger investigation. In this initial phase,
the authors were primarily interested in
\vilether certain factors could possibly
af-fect the level of intellectual functioning of
children with diabetes as measured by I.Q.
tests. These factors are age of onset of the
illness, duration of the illness at the time
of examination, and tile number of episodes
of hypoglycemia and acidosis.
PROCEDU RE
The subjects were 38 children with
dia-betes meliitus receiving their total medical
care at University Hospitals of Cleveland.
The age range of these cilildren was from
3 years 1 month to 18 years 6 months, with
a mean age of 10 years. The group of
chil-dren being followed is comprised of those
cllildren ordinarily followed in a University
Hospitals Outpatient Department plus all
tile diabetics referred as private patients to
one of us (W.B.W.). Thus a wide range of
socioeconomic levels is represented. In an
attempt to control factors such as
environ-mental background, educational
opportuni-ties and geographic location, one sibling
from each family was randomly selected
and tested.#{176} Tile age range of the siblings
was from 3 years 1 month to 17 ears 3
ITflOIltils, \Vitil a mean of 9 ‘ears 4 months.
Tile Stanford-Binet Intelligence Scale,
Form was administered individually to
each child. The variable used in testing all
0 The only factors not controlled by this popula-tion were age and sex. Previous investigations on intellectual functioning indicate that there is no
significant difference in intelligence between sexes.
To have used a population which would have con-trolled for the age factor would have meant
05
1
cv)
z
w
4 a
(0
z
0 a
MEANS OF GROUPS
+30 S ONSET UNDER 5,
S ONSET 5 AND OVER)
+20 C
+10
0 #{149}
-to .----. . . S S
-20 #{149} .
-30
I 2 3 4 5 6 7 8 9 0 II 12 3 4
AGE AT ONSET I YEARS
MEsNS OF PAIntED l.(. DIFFEI0ENCJ;s BY AGE AT
ONSET OF I)IABETES
.lge at Onset
<Syr >.ijr
Number of pairs of sil)hllgs
Average differenee iii I.Q. Sample \.ariafl(.e*
13
- loiS 115.3
‘2.5 ± 0.720
‘261.5
* Sample variance svas caictilated an:
(X)#{176}
52 101- 1
hypotheses was the difference in I.Q. score
between a diabetic and his sibling (diabetic
I.Q. minus sibling I.Q.). If a specific factor
has no effect upon the intellectual
func-tioning of children with diabetes, then the
differences, when classified according to
that factor, would tend to have an average
value of zero throughout, rather than a
trend with changing values of the factor.
With regard to age at onset, the I.Q.
differences were divided into two groups:
those for diabetics whose disease was
diag-nosed before tile age of 5 years and those
for diabetics who became ill at or after the
age of 5. A mean difference was computed
for eacil group and compared. Age 5 was
selected as a point of division for two
rea-sons. Experience in the treatment of
emo-tionally disturbed children has
demon-strated that traumatic experiences sHell as
hospitalizations, surgical procedures,
sepa-rations, etc., before the age of 5 are
infi-nitely more significant for future
develop-ment than are the same experiences after
this age. It is known that children under
5 years have only limited personality
re-sources available for the handling of such
disturbing events, and therefore the
possi-bility of pathologic sequalae is greatly
en-hanced. The second reason tilat led the
authors to choose this age is that the most
striking structural maturational cilanges in
the infantile brain are largely completed
during the first 5 postnatal years, and if any
disturbance in carbohydrate metabolism
occurs while the maturational process is
going on, the likelihood of irreversible
or-ganic damage occurring is increased.
Other factors were investigated as
cx-plained under the sections entitled
“Re-sults” and “Discussion”. The number of
episodes of hypoglycemia and acidosis were
obtained and quantified as follows. The
only hypoglycemic episodes enumerated
were those in which convulsions occurred
or those in which tile child was seen in a
Ilospital emergency ward or was admitted
to a hospital for this complaint. The
epi-sodes of acidosis tllat were counted were
limited to those in wilicil the child was
FIG. 1. I.Q. differences according to age at onset of diabetes.
admitted to tile hospital and analytic
docu-mentation of tile disturbance was
con-firmed.
RESULTS
Effect of Age at Onset
Detailed data on effect of age at onset of
diabetes are plotted in Figure 1 and are
summarized in Table I.
A t test on the differences shown in Table
I gave t=2.13, or a p value slightI’ less
thaii 0.05, indicating that age at onset does
Ilave an effect on the intellectual
function-ing of children Vitil diabetes.
It is also interesting to note that separate
+30
0
z
+20
(I)
I
‘:j#{149}
-. -tOe- o
Ui 0 0
U
z . 0
-20
w 0
a.
-30 OONSET UNDER FIVE
ci 0 #{149} YEARS OFAGE
0 I 2 3 4 5 6 7 8 9 10 II 2 3 4
TOTAL NO. OF EPISODES
Lengt/v of Illness at Time of
Examination
<‘2 yr ‘21110
>‘2 yr ‘2
10+
9
-8+ (9)
11-t 11-tes11-ts indicate that tile mean I.Q. difference
for the group Witil age of onset under 5
years is significantly different from zero
(p <0.02), and that for the other group is
not. Therefore, it appears that children who
become diabetic before the age of 5 years
suffer 5OIll intellectual illipairment, and
those who become diabetic after this age
show no such decrement.
Effect of Length of Illness
It is apparent that age of onset and
dura-tion of disease at time of testing could be
related. #{176}Accordingly, a more meaningful
test of the effect of length of illness would
be one in which tile sample was controlled
On age of onset. In order to do this a
so-called nonparametric technique1 was used.
The I.Q. difference for those with a total
duration of less than 2 years and those
with duration of more than 2 years in
each age group was compared with the
medians for the two age groups as to
whether they were above ( +
)
or below( -)
the median. The data were then examined,
as shown in Table II. It is apparent
with-out a formal test that length of illness does
not affect the I.Q. differences.
Effect of Episodes of Hypoglycemia
and Acidosis
The data indicated a negative
relation-ship between I.Q. difference and the total
number of both types of episodes only for
patients in whom the onset occurred before
5 years of age (Fig. 2). The number of
epi-sodes of each type were generally too few
or too concentrated around a few values
to permit meaningful separate analysis.
Episodes occurring both before and after
the age of 5 were counted. Although the
data are suggestive, it turns out that the
negative linear regression coefficient (onset
before 5 years) of I.Q. difference on number
0 Patients with early onset (roughly before 7
years of age) tended to have a higher average
duration of illness and a much wider range of
dura-tion than patients with late onset, but these points
were not subjected to statistical test.
Ftc:. 2. 1.9. differences according to total number
of episodes of hypoglycemia and acidosis.
of episodes is not significantly different
from zero (p >0.10).
Because siblings were used as controls,
age, of course, could not be controlled. In
order to ascertain whether diabetic-sibling
age differences were affecting I.Q.
differ-ences, an analysis using the same method
145lfl Table II was undertaken.
It is apparent, without a formal test,
that diabetic-sibling age difference does not
affect I.Q. difference.
‘I’MiLE It
EFFECT OF LENGTH OF 1LI.NES ON I.Q.
DIFFER-ENCE,* WITH AGE OF ONSET CONTROLLED
Age at Onsetf
< 5 yr >5 Totals
7+(6.7)
‘2-
7-3+(3.7) 5+5.3)
.5-‘I’v)tal 13 ‘25 38
* I.Q. differences are compared with medians for each
age group (+ indicating above and - ,below). Figures in parentheses indicate expected number of
observa-tions above medians if length of illness had ISO relation-ship to I.Q. difference.
.)
-ARTICLES 767
‘I’ABLE Ill
EFFECT OF’ l)IABI;Tu-SIBLING AGE l)IF’rF:IF:NCF: ON I.Q. l)zFFEIIINeF:, V1TI1
AGE AT ONSET CONTROLLED
.lge at O,vset5
<5 r j >; IOt(lI
ihling older thou ulialvetir 4+ (4. ‘2 3+ (4.3) 9+ (8. .5)
4-
9-‘il)ling younger thou diabetic ‘2+ (1.8) 7+ (7.7i . 9+ (9..51
9-
11-lotal 13 ‘23 38
* I.xpecte(I ‘aliucs are given ill parcut leses.
COMMENT
As has been stated, though much
atten-tioll has been given to the problem of
intel-lectual functioning of diabetic children,
previously reported research presents
evi-dence to support contrary views. A review
of these studies indicates that there have
been three implicit ilypotilesis underlying
a majority of these studies. The first
as-sumes that children with diabetes are
prob-ably of lower than average intellectual
ability. Teagarden2 summarized the
rea-soning for this position by stating:
There are reasons for thinking that neurological and psychological functions may be impaired by diabetes and that insulin shock may produce neurological damage. Therefore, it seems unlikely that diabetic children as a group will be superior intellectually. There is no biological reason why they should be superior.
The second hypotilesis assumes that
dia-belie children possess higher than average
inteiligence.#{176}8 The underlying assumption
is that because of the physical limitations
often imposed upon these children, they
compensate for this by excessive emphasis
upon intellectual activities.
By far the largest group of
investiga-tors#{176}14 suggest that the intelligence of
children with diabetes is normally
distrib-itted and does not differ significantly, in
either direction, from that of the total
popu-lation.
\Vhen one reviews tile previous work
ac-complished in this area it is clear that many
of the factors known to affect intelligence
were not sufficiently controlled to rule out
tile possibility of bias. The major factor
ig-nored in almost all of the investigations
re-ported was socioeconomic standing. It is a
well-established fact that socioeconomic
background is positively correlated with
level of intelligence as measured by
stand-ard I.Q. tests. Yet of all the studies quoted,
only one9 achieved any measure of control
over this very important variable. Those
studies in which lower I.Q.’s were found
among diabetics, wllen compared with
na-tional norms, were based on samples drawn
from clinic populations and therefore from
lower socioeconomic backgrounds.” 0’
Those investigations indicating that diabetic
children are of higher than average
intelli-gence were based on samples from private
patients of higher socioeconomic levels.2 7. S
Because the number of diabetic patients
available to any one clinical investigator is
limited, it is nearly impossible to select a
sample that faithfully reflects the
socioeco-nomic distribution of the population and
other possibly important variables. It is
extremely doubtful, therefore, if the
under-standing of the intelligence of children with
diabetes can be furthered by simply
com-paring the mean I.Q. of randomly acquired
patients with published national norms. As
a result of this limitation, it becomes
768
all-or as many as is possible-of the
varia-bles known to affect the measurement of
intelligence. Unless one uses such a control
group and attempts to equalize the effects
of socioeconomic background, age,
educa-tional opportunities and sex, little can be
scientifically stated from the mere testing
of children with juvenile diabetes. Only
Brown and Thompson’ used an adequate
control group. In 28 of their cases the next
oldest sibling was also tested. White used
a control group matciled for age, but the
control of just this one variable is not
suffi-cient. In the present study, the use of
sib-hugs as control subjects served to take into
account socioeconomic, ethnic, geographic
aild environmental factors that could affect
I.Q.
Another serious limitatioll of the previous
studies is tile lack of any systematic attempt
to assess the relative importance of factors
such as age of onset, the duration of illness
at the time of examination and the nuflll)er
of episodes of hypoglycemia and/or
keto-acidosis. In light of the first hypothesis,
wilicil assumes that diabetes has a
degen-erative effect upon intelligence, it is
un-usual tllat more longitudinal studies
in-volving follow-up investigations and
retest-ing were not attempted. Fischer and
Dol-ger,” who also deplore the lack of
long-term investigations, did retest 10 patients;
but this, of course, is an extremely small
sample.
Although the studies mentioned were
concerned with the I.Q. status of diabetics
in general in relation to the total population,
in view of the finding that age at onset
may have some bearing on I.Q., tile
useful-ness aild validity of such an over-all verdict
is questionable. Such a verdict from tile
present sample, for purposes of comparison,
cOtil(l be done only if it is reasonable to
as-sume that this sample reflects tile general
population of child diabetics by age at
on-set. We have little evidence to make this
assumptioll, but if made, our sample
indi-cates an over-all judgment that there is no
I.Q. difference between diabetics and their
nondiseased siblings. A comparison of the
over-all Illd1l I.Q. differeilce of our sample
with zero produced a t value of - 1.18,
wilich is not significant.
The preponderance of children with
on-set after 5 years of age in our sample
ob-scured the importance of age of onset when
an over-all judgment was made. If the
im-portance of age at onset is borne out by
additional studies or by extension of our
OWIl series, it would seem imperative to
determine the etiology of this I.Q. loss.
The data on episodes of severe
hypogly-cemia and acidosis as related to loss of
in-tellectual capacity in the young diabetic
indicate that either or both of these
meta-boiic disturbances could be important. It is
intriguing that the one child witil three
episodes of loss of diabetic control, and
whose I.Q. is 33 points below that of her
sibling (Fig. 2), has an I.Q. of 109; tile
sib-1mg has an I.Q. of 142; another sibling (not
tile randomly selected one) has an I.Q. of
129. Furthermore, the child had a peculiar
episode of apnea at age 2 years (prior to
diabetes) in w’hich mouth-to-mouth
resusci-tation was required, and normal respiration
(lid not return for a period of about 30
minutes. If tilis value were not included,
tile slOi)e would be significant, with a p
value between 0.02 and 0.05. However. we
feel tllat we have no firnl basis for
exciud-ing tilis observation. Tile apneic episode
\V15 (liscOvere(1 accidentally, and there was
110 systematic search for events of this type
prior to tile Ollset of diabetes. While the
present data do not implicate hypoglycemia
and acidosis as possible causes of loss of intellectual functioning, the final resolution
of this question must await a larger sample
aild/Or tile development of a more precise
method of counting episodes.
Prolonged llypOglycenlia has been related
to mental deterioration, and whether the
relatively brief periods observed in diabetes
is important reIllaiIlS to be determined. Tile work of Ketv et (1l.’ on tile correlation of
de-crease in cerebral oxygen uptake with
in-crease of ketones in serum in diai)ctic
acidosis would indicate tilat episodes of
ARTICLES
769
in the decreased I.Q. of tile preschool
dia-betic as well.
It would have been more desirable to test
each of these types of metabolic
disturb-ances separately and to limit the episodes to
those that occurred prior to 5 years of age,
but the relative infrequency of these severe
aberrations in control and the small size of
the group made this impossible.
The amount of hypoglycemia and
acido-sis occurring after 5 years of age does not
appear to affect I.Q. in this group of
pa-tients. The data indicate no relationsilip
whatever between the diabetic-sibling I.Q.
differences and the number of episodes of
acidosis and hypoglycemia for the group
with onset after 5 years of age.
Other metabolic abnormalities are known
tilat lead to mental deterioration in the
early years of life but do not have such an
effect in older children. Galactosemia and
phenylketonuria do not produce continuing
loss of mental functioning after the
in-fancy period. Hypothyroidism is not
asso-ciated with permanent cerebral damage
when the onset is in later childhood, in
con-trast to the retardation associated with
crc-tinism. Severe jaundice is not a factor in the
production of mental deficiency in older
in-dividuals, but it certainly has an effect on
the newborn. Thus it does not seeni
un-reasonable that the young diabetic may
have some loss of I.Q. as a result of early
metabolic disturbances that do not produce
damage in later childhood.
An alternate hypothesis has already i)een
suggested, namely, that the impact of a
chronic illness on a child under 5 ‘ears
results in some degree of intellectual loss.
The critical factor appears to be tile
imma-turity of the personality. By the time the
average child reaches 5 years of age he has
matured sufficiently to handle successfully
many events that might have been upsetting
at an earlier age. This fact has been
recog-nized for years by educators, who have
established the age of 5 years as the critical
age for the beginning of school. The child
under 5, however, does not have tile
re-sources available to his older counterpart
and is mucil more Vulllerable to
environ-mental stress. Therefore, the onset of
dia-betes with all of its ramifications tends to
overwhelm the younger child. Much of his
mental energy that would normally be used
for sublimated intellectual activity remains
bound by the illness and unavailable for
Sucil pursuits.
The specific dynamics involved in tile
intellectual loss are not known, but two
possibilities have suggested themselves to
the authors during the course of this
in-vestigation. Because the child under 5 has
only an incomplete picture of himself, tile
onset of diabetes has an especiall’
disrupt-ing effect on this development. Tlle child
tends to feel himself damaged, different
and worthless, and this attitude becomes
translated into feelings of inadequacy in
intellectual endeavors. It also seems that
(liabetes disrupts the normal growth of
independence, both mental and physical, so
that tile child does not feel capable of
ade-quate, independent functioning.
Because of the small size of the present
sample, the findings must be considered
tentative. However, because of tile
import-ai#{236}ceof this finding, the authors hope other
investigators of childhood diabetes will
consider the collection of similarly
con-trolled data, so that the numbers of cases
could be expanded in an attempt to settle
tiliS important (luestion. For our part. we intend to retest the diabetics and their
siblings regularly to determine if tile above
difference persists, and to expand the study
to include children with other chronic
ill-nesses.
SUMMARY
I.Q. tests were administered to 38 pairs
of diabetic and nondiabetic children. In
each family the nondiabetic child was a
randomly selected sibling of the diabetic
cilild. No relation was found between 1.9.
difference (diabetic I.Q. - sibling 1.9.) and
duration of illness. Children in whom
dia-betes began before the age of 5 years had
significantly lower I.Q.’s than their
difference between the diabetic and his
sib-ling when the disease began after 5 years
of age. A suggestive relationship (but not
statistically significant) was found between
the number of episodes of hypoglycemia
and acidosis and the magnitude of the I.Q.
difference between diabetics and siblings
for those with onset of disease before 5
years of age.
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