Microcephaly in a Normal School Population

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Microcephaly

in a Normal

School

Population

Clifford J. Sells, M.D.

From tile Department ofPediatrics and the Child Development and Mentd Retardation Center, University of

Washington, Seattle

ABSTRACT. Heights, weights, and head circumferences were ol)tailled on 1,006 students, ages 5 to 18 years, attending regular classes in four schools in a suburban Seattle school district. From the 1,006 students initially examined,

19 (1.9%) had a head circumference two or more standard deviations below the mean for age and sex.

Intelligence (ltOtiel1ts and academic achievement scores were ol)tamed on these children and compared with normal controls. No significant difference was found between mean IQs of the study subjects and the controls (99.5 es. 105), but

mean academic achievement scores were signi6cantl lower in the study sLIl)jeCts (49 rs. 70; P < .001). In addition,

although mean IQs were not significantly different between those subjects whose head circumference was proportional and those whose head circumference was relatively small, mean academic achievement scores were signthcantlv higher (60 cs. 39: P < .02) in those subjects whose head size was pFO)OLt iOILtl . Pediat,ic.s. 59:262-265, 1977. i I(ROCEPIIA LV, INTELLICEN(:E, (ROWTII ANI) I)EVELOPMENT.

A number of investigators have reported a

significant relationship between intelligence and

head size. Mentally retarded individuals are more

likely to have smaller heads than normal

individ-uals and are more apt to be shorter.3 On the

other hand, gifted children tend to have large

heads, and to have above-average heights and

ISeveral authors have suggested that the

diagnosis of microcephaly carries a grave

prog-nosis for normal intellectual functioning. 6 In

addition, among microcephalic children, IQ has

been shown to correlate directly with head

circumference.

The majority of studies which have examined

the relationship between head size and

intelli-gence have dealt with populations biased toward

mental deficiency. Few studies have looked at

microcephaly in normal populations. Nelson and

Deutschberger, analyzing data from the

collabo-rative project, found that children with the

smal-lest head size (approximately -2.5 SD) at 1 year

of age had a 50% risk of having an IQ below 80 at

4 years of age. The collaborative project data, in

addition to demonstrating a direct association

between head circumference and IQ in preschool

children, suggested that, given any head size, IQ

rises as body length increases. More recently,

Weinberg et al., studying 8- and 9-year-old

Caucasian boys, attending regular schools, found

a direct relationship between head circumference

and intelligence when socioeconomic status was

controlled.

The paucity of data in the literature dealing

with microcephaly in normal school populations

provided the impetus for this study. The purposes

of this study are: (1) to examine the prevalence of

microcephaly, defined as a head

circumfer-(Received Febniary 3; revision accepted for publication May 4, 1976.)

Supported in part by Project No. 913, Maternal and Child Health Services, Bureau of Community Health Services, DHEW.

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TABLE I

IQ AND ACADEMIC AcHIEvEMENT SCORES FOR 19 N’IICROCEPHALIC CHILDREN ENROLLED IN PUBLIC SCHOOLS

0

AsstIIfleS < :3% = 3% for calculation of mean.

RESULTS

ARTICLES 263

ence 2 SD below the mean in a normal school population; (2) to determine IQ and academic

achievement of individuals with a head circum-ference 2 SD below the mean: and (3) to evaluate the association between height and IQ

and academic achievement in these individuals.

METHODS AND MATERIALS

During the spring of 1972, 1,006 students, aged

5 to 18 years, attending regular classes in two

elementary, one junior high, and one senior high

school in a Seattle area suburban school district,

were examined. The school district participating

in the study has a very small minority population

with more than 95% of the students being

Cauca-sian. The four schools were selected to give a

broad socioecononi ic cross-sectional sample and

were felt by district officials to be representative

of the entire district’s student population

(approx-imately 14,500 students). Approximately 80 students, one half boys and one half girls, in each

grade level (kindergarten through 12th grade)

participated in the study. Participation was

voluntary, but no student refused to participate.

From the 1,006 students who were initially

exam-ined, 19 were found to have head

circumfer-ences 2 SD below the mean for age and sex’

and form the subjects of this study. Table I depicts

the age, sex, race, height percentile, weight

percentile, intelligence quotient, and academic

achievement score for the 19 subjects.

Ages were recorded the nearest half-year.

Head circumference was measured by the author

to the nearest 0.5 Cm using a flexible steel tape

applied above the supra-orbital ridges

anterior-ally and posteriorally over that part of the occiput which gives the maximum head circumference.

Heights were measured in the erect position by

standard procedures to the nearest 0.25 inch with

subjects in stocking feet. \Veights were measured

in street clothes or gym suits without shoes to the

nearest 0.25 lb. Weights and heights were

converted to percentiles using data froni either

the Department of Maternal and Child Health,

Harvard School of Public Health (Stuart data) or

from the Iowa Child \Velfare Research Station,

the State University of Iowa.

All IQs and academic achievement results were

measured by standardized group or individual

tests done at the four public schools involved in

the study. The ‘ was the

primary group intelligence test used (eight students) while the \Vechsler Intelligence Scale

for Children (WISC)’2 was the individual

intelli-gence test used (two students). When more than

Subject Age Race Sex Height Weight IQ Academic

(yr) (#{176}4)) (%) Achievement

(National %)

1 16#{189} W F 7 10 107 60

2 17’2 \\ F 50 10 - 55

3 14#{189}\V F JO 50 108 41 4 11 \‘ F <3#{176} <3#{176} - 70

5 8”2 \\‘ F 50 25 99 45

6 5/2 \V s1 10 25 91 57

7 16 i X) 75 98 31

S 15#{189} Mi() 25 - 23

-i-

15#{189}W’ Nl <3#{176} - 68

10 9’2 \V \I 2525 90 16

-i-i--

182 \V F < 3#{176}< 3#{176}- 48 12

-16#{189} \V F<3#{176} < 3#{176}- 47

13 15’.’2 \V F 6 15 95 56

14 14#{189} \ F 3 8 129 81

15 13’ \‘ F :35 10 115 65

16 12 \V F 40 40 74 6

17 9#{189}\V F 4 10 100 41

18 1 \V NI 10 10 - 47

19 12#{189} \VM 5 7 88 67

Mean 20 19 99.5 49

one test result was available, the most current

score was used. In one student; where both the

Lorge-Thorndike and the \VISC were

adminis-tered, the results of the latter were used for data

analysis even though the two tests resulted in virtually identical scores. Seven students did not

have IQ data available for analysis as they were

not enrolled in the district at the time their class

had psychological testing, but all at the time of

the study were doing satisfactory schoolwork in regular classrooms. A number of academic

achievement tests were used depending upon the

child’s age, but the test used in most instances was

the Comprehensive Test of Basic Skills (CTBS).’3

\Vhen more than one achievement test score was

available, the most current was used. All

academ ic achievement test results are averages

expressed in national percentiles.

The overall prevalence of microcephaly in this

normal school-age population was 1.9%. The 19

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TABLE II TABLE III

MEAN IQ AND ACADEMIC ACHIEVEMENT SCORES FOR

MICROCEPHALIC SUBJECTS AND CONTROLS

Scores Subjects ,---No. Score Controls t-test ____k___ t P

Mean IQ 12 99.5 105.0#{176} 1.34 NS

Academic 19 49 70t 4.80 .001

achievement (mean percen-tile)

#{176}sIeanscore of sixth-grade students on the Lorge-Thorndike Intelligence Test.

tMean score of tenth-grade students on the Comprehensive Test of Basic Skills.

microcephalic subjects’ head circumferences

were all between -2 and -3 SD from the mean.

Table II compares the mean IQs and academic

achievement scores of the study subjects with

normal controls. No significant difference was

found between mean IQs, but mean academic

achievement scores were significantly lower in

the study subjects (P < .001). Table III compares

subjects whose heights are 10th percentile

with those subjects whose heights are < 10th

percentile. Those study subjects whose heights

were 10th percentile had a lower mean IQ

than those subjects with heights below the 10th

percentile. Although mean IQs were not

signifi-cantly different between those subjects whose

head size was proportional to body size and those

subjects whose head size was relatively small for

body size, i.e., head circumference 2 SD below

the mean with a height 10th percentile, mean

academic achievement scores were significantly

higher in those subjects whose head size was

proportional (P < .02).

DISCUSSION

Although head circumference measurement

remains a valuable clinical tool,a head

circumfer-ence measurement 2 SD below the mean is not

uniformly associated with mental retardation. In

our study of 19 microcephalic children, only one

had an IQ of less than 80 and none at the time of

the study required remedial educational

mea-sures. Since our population was selected from

children attending regular classrooms, mentally

retarded children with microcephaly would not

be included in the study population. That none of

our children had a head circumference of more

than 3 SD below the mean is not surprising as it

has been shown that, among microcephalic

chil-Mwm IQ AND ACADEMIC ACHIEVEMENT Scoiss OF MICROCEPHALIC SUBJECTS BY HEIGHT

Scores Subjects’ Height t-test

Percentile

.

-

___*___

lOth <10th t P

IQ scores No. of subjects

.

7 5

Mean score 96 104 0.88 NS

Academic achievement scores

No. of subjects 10 9

Mean percentile 39 60 2.79 .02

dren, IQ is directly related to head

circumfer-7Our study supports the hypothesis that a

small brain, as reflected by a head circumference

of between -2 and -3 SD, does not in itself

produce mental retardation. Rather, it is the

various cerebral malformations that become

increasingly prevalent at the lower and upper

extremes of head size which are responsible for

mental retardation.

Not only was none of the microcephalic

chil-dren in this study retarded, but in addition the

mean IQ of this group was not significantly

different from the mean IQ of all sixth-grade

children enrolled in the school district. Hence, at

least in this school-age population, regular

class-room children with a head circumference

between -2 and -3 SD have a mean IQ not

significantly different from the population in

general. These children, however, although

comparable to the national average on standard

achievement tests, performed significantly below

the district’s average (49th percentile vs. 70th

percentile; t 4.80; P < .001).

The finding of a 1.9% prevalence of

microceph-aly in a normal school population was not unexpected, since the author anticipated that

there would be a significant number of children

with microcephaly and normal intelligence

enrolled in regular classrooms. The selection

factor of microcephaly associated with mental

retardation resulting in special education

place-ment undoubtedly resulted in an artifically low

prevalence figure, however, since only regular

education students were examined.

It is generally believed that head

circumfer-ence should be evaluated with reference to

height. O’Connell et a!. ‘s data suggest that

chil-dren with growth failure and normal intelligence

have normal head circumferences. Nelson and

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ARTICLES 265

concluded from a review of the collaborative data

that, with respect to IQ for children with small

heads, the less proportionate the head to the body

length, the better. Admittedly, the numbers are

small, but the data presented in this study do not

support such a conclusion and, in fact, at least with respect to academic achievement, suggest

that individuals with disproportionately small

heads may do less well in school than those

children with small heads but heads proportional to their height.

The incidence of normal intelligence in

micro-cephalicchildren is unknown, but may be higher

than is generally appreciated. Clinicians

gener-ally diagnose microcephaly when their patient has a head circumference which falls 2 SD

below the mean for age and sex. They then

frequently assume that their patient is in all

likelihood mentally retarded. Suth an assumption

appears to be unwarranted. Microcephaly,

nonetheless, remains an important clinical sign.

Although it correlates with it is not synonomous

with mental retardation.

REFERENCES

1. Brandoii MWG, Kirman BH, Williams CE: Microceph-aly. J Ment Sci 105:721, 1959.

2. Culley WJ, Jolly DII, Mertz ET: Heights and weights of mentally retarded children. Afli J Ment Defic

68:203, 1963.

3. Mosier HD, Grossll1an HJ, Dingn3an HF: Physical

growth in mental defectives: A study in an institu-tionalized population. Pediatrics 36(suppl):465, 1965.

4. Terman LM (ed): Genetic Studies of Genius: Volume I. Mental and Physical Traits of a Thousand Gifted Children, ed 2. Stanford, California, Stanford University Press, 1926.

5. O’Connell EJ, Feldt RH, Stickler GB: Head circumfer-ence, mental retardation and growth failure. Pediat-rics 36:62, 1965.

6. Davies H, Kirman BH: Microcephal. Arch Dis Child

37:623, 1962.

7. Pryor HB, Thelander HE: Abnormally small head size and intellect in children. J Pediatr 73:593, 1968. 8. Nelson KB, Deutschberger J: Head size at one year as a

predictor of four-year I.Q. Dev Med Child Neurol

12:487, 1970.

9. Weinberg WH, Dietz SC, Penick EC, McAhister \TH: Intelligence reading achievement, physical size, and social class. J Pediatr 85:482, 1974.

10. Nellhaits G: Head circumference from birth to eighteen years: Practical composite international and inter-racial graphs. Pediatrics 41: 106, 1968.

1 1. The Lorge-Thorndike Intelligence Tests. In, Buros OK (ed): The Sixth Mental Measurements Yearbook. New Jersey, Gryphon Press, 1965, p 468.

12. \Vechsler D: The \Vechsler Intelligence Scale for Chil-dren Nianual. New York, Psychological Corp,

1949.

1:3. Comprehensive Tests of Basic Skills. In, Buros OK (ed): The Seventh Mental Measurements Yearbook. New Jersey, Gryphon Press, 1972, p 8.

ACKNOWLEDGMENT

I am indebted to Dr. Gerald D. LaVeck for his critical review of the manuscript and to Ms. siarilyn Bonifaci for her assistance in the preparation of the manuscript.

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1977;59;262

Pediatrics

Clifford J. Sells