Clinical Genetics 1987: 3 2 24-27

Predicting 47,XXY boys

intellectual functioning in from characteristics of sibs

C. N~TLEY The Hospital for Sick Children, Toronto, Canada

Observations on the intellectual and educational functioning of neonatally identified 47,XXY boys and their sibs are presented. Equations for predicting the intellectual abilities of extra X boys on the basis of those of their sibs are provided. These may be useful to professionals engaged in counselling parents or possible parents of 47,XXY males.

Received 26 November 1986, accepted for publication 1 March 1981

Key wordr: 47.XXY; intelligence; prediction; school performance.

There have been a number of reports (Niel- sen et al. 1982, Robinson et al. 1982, Walzer et al. 1978, 1982) which have indicated that neonatally identified 47,XXY males fre- quently have lower verbal than performance 1.Q.s when tested during childhood and early adolescence. Investigators have also reported that many of these boys have difli- culties in learning, particularly in such areas as reading and spelling (Stewart et al. 1982, Walzer et al. 1982). However, individual dif- ferences in intelligence and school perform- ance are large (Puck et al. 1983), making it difficult for those involved in counselling to advise parents or potential parents about the intellectual implication of a 47,XXY karyotype. In this paper I present data derived from

intellectual and educational assessments of neonatally identified 47,XXY boys and their available sibs. They are reported in a form which provides the possibility of predicting cognitive Functioning of 47,XXY males on the basis of psychometrically de- fined characteristics of their sibs.

Material and Methods

The majority of 47,XXY boys to be report- ed on were identified by amnion cell exam- inations of 72,739 newborns conducted by Bell & Corey (1974). One case was added to the forty-one 47,MY boys identified by this method as a result of chromosomal studies of the immediate families of new- born 47,XXY boys (Bell & Cripps 1974). No other family members were found to have an extra X cell line. Thirty-three of these 42 cases have participated at various times in an ongoing prospective study of growth and development in X and Y ane- uploid children conducted at The Hospital for Sick Children, Toronto. During the course of this research, attempts have been made to assess a chromosomally normal sib of each proband. Whenever possible, the male sib closest in age to the extra X boy was assessed.

Each proband was assessed with the Wechsler Intelligence Scale for Children - Revised (WISC-R; Wechsler 1974) and the

I Q I N 47 ,XXY BOYS A N D SIBS 25

Wide Range Achievement Test (WRAT; Ja- stak et al. 1978). The former provides esti- mates of verbal, performance and full scale 1.Q.s and the latter estimates of skills in reading, spelling and arithmetic. Sib con- trols were tested with the WISC-R or, when older than 16, with the Wechsler Adult In- telligence Scale (WAIS; Wechsler 1955). Their educational skills were also assessed using the WRAT.

Intellectual test results were obtained on 24 pairs of 47,XXY boys and their sibs. Among the sibs, 16 were male and eight female, 20 being tested with the WISC-R and four with the WAIS. Complete WRAT data were obtained on 23 pairs of probands and sibs, of whom I5 were male and eight female.

Results

Group Differences The intellectual and educational test results for the 47,XXY boys and their sibs are pres-

ented in Table 1. This table also provides the mean ages at testing for the two groups. Although the extra X boys were significant- ly younger than their sibs when intellectu- ally examined, this is unlikely to have dis- torted the results since their WISC-R results have been found to be nearly identical when they were retested at a mean age of 13.2 years (Stewart et al., in press). Correlated t- tests on the remaining data indicated that the 47,XXY boys obtained lower mean ver- bal and full scale 1.Q.s than their sibs and also performed below them in reading, spelling and arithmetic.

Inter-Group Correlations Table 2 presents the product moment corre- lations between the intellectual test results of probands and sibs. As can be seen, the verbal, performance and full scale 1.Q.s of the probands are significantly correlated with the corresponding 1.Q.s of their sibs. Table 3 provides the correlations between

Table 1

Wechsler Intelligence test and WRAT test results for 47,XXY boys and sibs. All scores have normative means of 100 and standard deviations of 15.

W h a l e r Results (24 pairs of observations) 47,XXY Sibs t P

Verbal 1.0. mean 84.75 90.38 7.096 <0.01

Performance 1.0. mean 101.79 102.33 0.180 NS

Full scale 1.0. mean 92.29 100.00 3.469 <0.01

Age (years) mean 9.12 11.81 2.766 KO.01

sd 15.52 12.35

sd 13.79 12.65

ad 13.49 11.63

sd 1.38 4.19

WRAT (23 pain of observations) 4 7 . W Sibs t P

Reading mean 09.70 101.52 4.574 CO.01 sd 16.03 15.05

sd 18.45 17.65

sd 12.79 14.14

sd 1.71 4.10

Spelling mean 85.57 99.40 3.324 <0.01

Arithmetic mean 81.13 95.61 4.733 <0.01

Age (years) mean 12.01 11.76 0.265 NS

26 NETLEY

T8ble 2

Product moment correlations between Wechsler test results of 47,XXY boys and sibs.

47,xxYs

Full scale I.Q. Verbal 1.0. Performance I.Q.

Sibs' Verbal I.Q. O.TT1" Sibs' Performance I.Q. 0.278 Sibs' Full wale 1.0. 0.828"

0.334 0.449' 0.454'

0.053- 041 g. 0.633-

' p<0.05. ** p<o.o1.

Table 3 Product moment correlations between WRAT attainment scores and Wechsler test results for

24 47,XXY boys and their 23 sibs.

4 7 , w WRAT Standard score

Readlng Spelling Arithmetic

Verbal I.Q. 0.823"' 0.822"' 0.832"'

Full scale I.Q. 0.718"' 0.582"' 0.780"' Performance I.Q. 0.372 0.333 0.468"

~~~

Si bs WRAT Standard score

Reading Spelline Arithmetic

Verbal 1.0. 0.813"' 0.708"' 0.830"' Performance 1.0. 0.413' 0.428"' 0.492' Full scale 1.0. 0.722"' 0.652"' 0.842"'

pxo.05. *' PK0.02. *** p<o.o1.

the intellectual and academic abilities of the extra X boys and their sibs. They indicate that the relationships between aptitudes and attainments are similar for both groups with verbal and full scale 1.Q.s most strongly associated with academic skills in each.

Predictive Equations Linear regression equations were computed between the intellectual test results of pro- bands and sibs using those I.Q. measures which were most strongly correlated (see Table 2). These are presented in Table 4.

Conclueions

The present data indicate that 47,XXY boys typically have lower verbal, and in conse- quence, lower full scale 1.Q.s than their sibs. They indicate also that the educational skills of the affected boys are below those of their chromosomally normal brothers and sisters. Although this evidence and that provided by other reports (for a summary see Stewart et al. 1982) support the conclusion that in- telligence, especially verbal ability, is de- pressed in extra X boys, the present results demonstrate that their intellectual aptitudes are significantly related to those of their sibs. Equations which exploit these associ- ations and provide a basis for predicting abilities in 47,XXY males are presented. These may be useful to those involved in counselling parents and those facing de-

Table 4

Equations for predicting Wechsler 1.Q.s on the basis of slb 1.Q.s.

47,XXY Verbal 1.0. -0 .W x sib verbal I.Q. - 10.529 47,XXY Performance I.Q. =0.48Q x sib performance I.Q. + 51.737 47,XXY Full scale I.Q. =0.734 x sib full scale I.Q. + 18.898

I Q I N 4 7 , X X Y B O Y S A N D S I B S 27

cisions arising from the prenatal diagnosis of extra X states.

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Walzer, S., P. H. Wolff, D. Bowen. A. R. Silbert, A. S. Bashir, P. S. Gerald & J. B. Richmond (1978). A method for the longitudinal study of behavioural development in infants and children: the early development of XXY children. J. Child Psychol. Psychiatry 19213-219.

Waizer, S. , J. M. Graham, A. S. Bashir & A. R. Silbert (1982). Preliminary observations on language and learning in XXY boys. Birth De- fects: Original Article Series XVIII, 185-192.

Wechsler. D. (1974). “Manual for the Wechsler Intelligence Scale for Children - Revised”. New York, The Psychological Corporation.

Wechsler, D. (1955). “Manual for the Wechsler Adult Intelligence Scale“. New York, The Psychological Corporation.

Address: C. Netley Psychology Department The Hospital for Sick Children 5SS University Avenue Toronto, Ontario Canada MSG 1x8