NOT CAUSAL LINK BETWEEN SQUINT AND CEREBRAL PALSIES, FROM
PREMATURITY AND / OR LOW BIRTHWEIGHT, IN DOWNS?
Renato
COCCHI, neurologist and medical psychologist;
Roberta
BRANCHESI, orthoptist, ophthalmology assistant.
Summary.
We investigated the link among the
outcomes in cerebral palsy (CP) and squint, in Downs prematurely born with / or
without low birthweight.
In a group of 90 persons selected
according to Susser et al., criteria. (1985), with one or both these risk
factors, we did not find any CP form, besides 26 squint cases.
As for this two risk factors and their
outcome in CP, the Poisson's distribution showed that random probability of
such an event is less than 0.04.
We cannot figure that the squint and CP
probability have the same cause in premature with or without with low
birthweight, since our sample lacking any CP. We may easily suppose that a
causal link between these two outcomes has very poor probability.
Key words: Down syndrome, prematurity,
low birthweight, CP outcome, squint outcome. epidemiology.
Down's syndrome
Mental retardation
Symptoms
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The congenital squint is a frequent symptom
in Down syndrome (trisomy 21), and it ranges from 32.84% of Lowe [1] to 27.91%
of our previous survey [2].
Its causes are unknown or only assumable,
but its great presence in cerebral palsied (CP) people - from 37-60%, reported
in Harcourt review [3] to 52.5-62% according to recent studies [4-7] - induced
Hugonnier and Hugonnier-Clayette to affirm that the causal factor is the same
[8].
Our attempt to relate risk factors for CP
and the concomitant presence or not of squint in Downs did not drive to
conclusive results [2].
Only prematurity or low birthweight, the
most important causal factors for CP, have their risk rates for the paralytic
outcome.
Another recent and cautious assessment had
its figuring in by Susser and coll. [9] and we decided to conform to it when we
dealt with this study.
Susser and coll. [9] divided these two risk
factors in five ways:
- weigh < 1501 grams, for any fetal age/
risk = 24.4%;
- weigh 1501-2500 grams, with the fetal age
<= 36 weeks / risk = 6.2%;
- weigh 1501-2500 grams, with the fetal age
of at least 37 weeks / risk = 1.8%;
- weigh 2500 grams at least, with the fetal
age <= 36 weeks / risk = 1.4 %;
- weigh > 2500 grams and the fetal age
=> 37 weeks (as normal age) / risk = 1.0%.
In a previous paper, one of us found that
Downs show little prevalence of CP as following of prematurity and low
birthweight.
This fact was attributed to an excess
presence, in Downs, of the supeoxide-dismutase enzyme and
glutathion-peroxidase. Both these enzymes are scavengers of oxygen free
radicals that form themselves in anoxia/ischemia conditions, even related to
prematurity or low birthweight [10].
That being stated, we carried out an
epidemiological study to see if there are some relationships between
prematurity and/or low birthweight, CP and squint in Downs.
Subjects, material and
methods. We reexamined all the
records of a consecutive not selected cohort of 424 people with 21 trisomy,
come from all the Italian regions to outpatients' consultation between 1979 and
September 1988 end.
Then, we sorted the records of those
prematurely born people with or without low birthweight, according to the over
described criteria of Susser and coll., [9].
Of the subjects fitting study criteria, we
besides collected sex; year by birth; chromosomal diagnosis; CP presence, out
of simple hypotonicity; squint presence, both actual or in past.
The Poisson's distribution served to
calculate probability we were dealing with a purely random result or results.
Results.
Ninety out of 424 subjects fitted the
selective criteria here chosen.
They were 64 males and 26 females, with a
males/females ratio = 246.15/100. All bore between the year 1962 and the year
1987, with the median on the year 1981.
The chromosomal diagnosis has shown this
distribution:
|
Pure trisomy 21 |
82 Ss |
91.11% |
|
Translocations |
5 Ss |
5.56 % |
|
Mosaicisms |
3 Ss |
3.33 % |
Prematurity and/or low birthweight were so
divided:
|
|
|
|
|
< 1501 g |
4 |
4.44 % |
|
1051 - 2500 g and <= 36 weeks. |
23 |
25.56 % |
|
1502 - 2500 g and 37 weeks. |
31 |
34.44 % |
|
>= 2500 g and <= 36 weeks. |
32 |
35.56 % |
|
Total |
90 |
100.00 % |
CP or squint finding:
CP = 0 Ss. = 0.00%;
Squint = 26 Ss = 28.98%;
Table 1: Statistical analysis of the results
for the CP outcome.
|
Risk factors |
Nr of Ss |
% of risk |
Expect. CP |
Observ. CP |
p (*) |
|
|
|
|
|
|
|
|
< 1501 g |
4 |
24.4 |
0.98 |
0 |
|
|
1051 -2500 g and <= 36 weeks. |
23 |
6.2 |
1.43 |
0 |
|
|
1502 -2500 g and 37 weeks. |
31 |
1.8 |
0.56 |
0 |
|
|
>= 2500 g and <= 36 weeks. |
32 |
1.4 |
0.45 |
0 |
|
|
Total |
90 |
|
3.42 |
0 |
0.327 |
(*) probability of a
random event according to the Poisson's distribution.
As for the relationship, in Downs, between
prematurity and/or low birthweight and CP, the Poisson's distribution has
pointed up that there is less of the 4% probability of a random result. In
other words, there is over 96% probability that the CP lack from prematurity
and/or low birthweight has a specific cause.
This group of 90 subjects does not have any
CP outcome, while there are well 26 squint cases. So, we cannot use statistics
to relate this two figures by each another, missing one of the terms.
Discussion.
About the selection criteria for the CP
presence, we excluded the hypotonicity because, we think, it is a symptom of
cerebellar dysfunction, as other authors wrote [11].
As for our results, it is interesting notice
that the prevalence of prematurity and/or low birthweight is more frequent in
males, with a M/F ratio about 2.5 to 1.
This ratio is different from what commonly reported
for the trisomy 21. It generally goes, for Italy, from 1.34 to 1 [12], being
from 1.36 to 1, in first 366 cases of this series [13]. In facts it is nearer
to what habitually found in child neuropsychiatry.
The % distribution of the chromosomal form s
of 21 trisomy parallels what we know for Italy [12-13] and for foreign
countries [11; 14-15].
This datum, together to the coming from
everywhere of Italy, points up that, excluding the altered M/F ratio, our
sample is representative at least of the Italian Down population.
Even using the risk percentage in the CP
outcome of Susser and coll. [9], as for the prematurity and/or the low
birthweight, we can confirm what already one of us found [10], although with
smaller evidence. A premature Down child with or without low birthweight is
less prone to CP risk than a not-Down child, born with same risk factors. This
becomes more striking if we bear in mind that more than 65% of these subjects
had suffered from at least two or three of those pre-, peri- and neonatal
troubles [2] that are considered symptoms of not otimality and CP risk factors
[16].
Having found 28.89% squint in prematurely
born and/or with low birthweigh Downs it is not much far from the 27.91% we
already saw in the first 215 cases of this same cohort [2].
The lack of CP in premature Down subjects
with or without low birthweigh (out of 424 subjects of the whole cohort, I
found only 3 CP of postnatal origin) leads to infer that these two outcomes, CP
and squint, have poor correlation, if not fully independent from eachother, at
least in this Down sample.
We have to see if the squint, in itself,
cannot be linked by another patrhway, different from the anoxia-ischemia, to
the prematuritaty and/or to the low birthweigh, or if it does not depend from
other factors, that, for now, we do not know at all.
We found 28.89% squint in prematurely born
with or without low birthweight Downs. It is not much far from the 27.91% we
already saw in the first 215 cases of this cohort [2]. The lack of CP in
premature Down subjects with or without low birthweight (out of 424 subjects of
the whole cohort, I found only 3 CP of postnatal origin) leads to imply that
these two outcomes, CP and squint, have poor correlation, if not fully
independent from each another, at least in this Down sample.
We have to see if the squint cannot be
linked by another pathway, different from the anoxia-ischemia, to the
prematurity and/or to the low birthweight. Perhaps also it does not depend from
other factors, which, for now, we do not know at all.
References
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First published on Internet on June 2002. Copyright by Renato Cocchi,
2002.
Author's address: dr Renato COCCHI, via Rabbeno, 3
42100 Reggio Emilia (Italy)
renatococchi@libero.it
Down's syndrome
Mental retardation
Symptoms
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