An extra X or Y chromosome: Contrasting the cognitive and motor phenotypes in childhood in boys with 47,XYY syndrome or 47,XXY Klinefelter syndrome
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AN EXTRA X OR Y CHROMOSOME: CONTRASTINGTHE COGNITIVE AND MOTOR PHENOTYPES INCHILDHOOD IN BOYS WITH 47,XYY SYNDROME
OR 47,XXY KLINEFELTER SYNDROME
Judith L. Ross,1,2* Martha P.D. Zeger,1,2 Harvey Kushner,3 Andrew R. Zinn,4
and David P. Roeltgen51Department of Pediatrics, Thomas Jefferson University, Philadelphia, Pennsylvania2Department of Pediatrics, duPont Hospital for Children, Wilmington, Delaware
3Biomedical Computer Research Institute, Philadelphia, Pennsylvania4Department of Internal Medicine, McDermott Center for Human Growth and Development,
University of Texas Southwestern Medical Center, Dallas, Texas5Department of Neurology, Georgetown University, Washington, DC
Objective: The goal of this study was to contrast the cognitive phe-notypes in boys with 47,XYY (XYY) karyotype and boys with 47,XXYkaryotype [Klinefelter syndrome, (KS)], who share an extra copy of the X-Ypseudoautosomal region but differ in their dosage of strictly sex-linkedgenes. Methods: Neuropsychological evaluation of general cognitive abil-ity, language, memory, attention, visual-spatial abilities, visual-motor skills,and motor function. Results: Study cohort: 21 boys with 47,XYY and 93boys with 47,XXY (KS), age 417 years, and 36 age-matched control boys.Both the XYY and KS groups performed less well, on average, than thecontrols on tests of general cognitive ability, achievement, language,verbal memory, some aspects of attention, and executive function, andmotor function. The boys with XYY on average had more severe and per-vasive language impairment, at both simple and complex levels, and theboys with KS on average had greater motor impairment in gross motorfunction and coordination, especially in running speed and agility. Conclu-sions: The results from these large XYY and KS cohorts have importantneurocognitive and educational implications. From the neurocognitivestandpoint, the presenting findings afford an opportunity to gain insightsinto brain development in boys with XYY and those with KS. From theeducational standpoint, it is critical that boys with XYY or KS receiveappropriate educational interventions that target their specific learningchallenges. These findings also provide important information for counsel-ing clinicians and families about these disorders. ' 2009 Wiley-Liss, Inc.Dev Disabil Res Rev 2009;15:309317.
Key Words: XXY; Klinefelter syndrome; XYY; sex chromosome
Two sex chromosome aneuploidy disorders, 47,XYYand 47,XXY (Klinfelter syndrome, KS), affect onlymales. Both disorders are relatively common and areunderdiagnosed. In addition, there may be confusion aboutwhat distinguishes one from the other. The XYY syndromeaffects one in 1,000 males and is characterized by physical
findings such as tall stature as well as neurological, cognitive,and behavioral phenotypes [Welch, 1985; Robinson et al.,1990; Ratcliffe et al., 1982, 1992; Aksglaede et al., 2008; Kentet al., 2008]. Testicular function, testosterone levels, and fertil-ity are usually normal [Rudd et al., 1968; Price and van derMolen, 1970; Baghdassarian et al., 1975; Benezech, 1985;Welch, 1985; Ratcliffe et al., 1994; Geerts et al., 2003; Aks-glaede et al., 2008]. KS, the most common sex chromosomedisorder [MacLean, 1961; Robinson et al., 1990; Rovet et al.,1995], occurs in 1 in 426 to 1 in 1,000 males [Bojesen et al.,2003]. Like XYY, the KS phenotype includes tall stature andcharacteristic cognitive attributes, but, in contrast to XYY, alsoincludes childhood onset testicular failure.
The cognitive phenotype in boys with XYY typicallyincludes normal to mildly diminished general intelligence asmeasured by full-scale intelligence quotient (IQ) [Benderet al., 1984; Evans et al., 1986; Netley, 1986; Robinson,1985], with Verbal IQ impaired more than Performance IQ[Christensen and Nielsen, 1973; Ratcliffe et al., 1982; Welch,1985]. These boys tend to have delayed speech developmentand to require speech therapy [Daly, 1969; Valentine, 1979;Ratcliffe, 1982; Bender et al., 1984; Robinson, 1985; Geertset al., 2003]. Often they have difficulty mastering school
Grant sponsor: NIH; Grant number: RO1NS050597 (J.L.R.).*Correspondence to: Judith L. Ross, MD, Department of Pediatrics, Division of En-docrinology, Thomas Jefferson University, 1025 Walnut Street, Suite 726, Philadel-phia, PA 19107. E-mail: firstname.lastname@example.orgReceived 27 July 2009; Accepted 4 September 2009Published online in Wiley InterScience (www.interscience.wiley.com).DOI: 10.1002/ddrr.85
DEVELOPMENTAL DISABILITIESRESEARCH REVIEWS 15: 309 317 (2009)
' 2009Wiley -Liss, Inc.
curricula and need educational supportservices in reading and writing [Benderet al., 1984; Netley, 1986]. Increasedrisk for hyperactivity and attentionproblems has also been reported [Ruudet al., 2005]. Boys with XYY also havedelayed motor milestones and impairedfine and gross motor function, coordi-nation, and tone [Ratcliffe et al., 1982;Bender et al., 1984; Robinson et al.,1985; Ratcliffe, 1999; Geerts et al.,2003].
The cognitive phenotype in boyswith KS is similar, with depressed verbalIQ relative to performance IQ in both inchildren and adults [Graham et al., 1988;Walzer et al., 1990; Rovet et al., 1995].This may be accompanied by moderateto severe problems with reading, spelling,writing, and arithmetic [Nielsen et al.,1981; Stewart et al., 1986]. Languageand speech impairments are evident insome form at all ages. Attention issuesrelated more to omission than commis-sion errors have also been described inchildhood in KS [Ross et al., 2008].
Thus, there appears to be someoverlap in the cognitive phenotypes inthese two disorders, especially in thearea of language dysfunction. However,in the absence of a systematic compari-son of these two groups, the similaritiesas well as the differences are not welldefined. The goal of this study was tocompare and contrast the cognitive phe-notypes in boys with XYY, boys withXXY, and age-matched control boys.
SubjectsSubjects were generally referred
to the pediatric endocrine clinic atThomas Jefferson University or wereself-referred. All were diagnosed withXYY or XXY (KS) by karyotype. Thestudy was approved by the HumanStudies Committee at Thomas JeffersonUniversity and UT Southwestern Medi-cal School. All subjects and their parentsgave informed consent and assent. Theclinical evaluation was performed atThomas Jefferson University and thekaryotyping was performed by the clini-cal cytogenetics laboratory at UTSouthwestern Medical School.
Anthropometric measurementsThe clinical assessment included
conversion of measurements to SDscores using age- and gender-specificnorms of height (by stadiometer),weight [Hamill et al., 1979], and head
circumference [Hall, 1995]. Pubertaldevelopment was assessed according tostandard methods [Marshall and Tanner,1993]. Testicular size was measuredusing standard Prader orchidometerbeads [Hall, 1995].
Cognitive and motor evaluationSubjects were individually admin-
istered a battery of neuropsychologicaltests specifically designed to assess mem-ory, attention, executive function, vis-ual-spatial abilities, visual-motor skills,and language. The evaluation wasadministered by trained and experiencedpsychometricians under the supervisionof a licensed neuropsychologist. Rawscores were converted to standard scores(mean of 100, standard deviation of 15),based on the test-specific norms or ourown population of age-matched controlchildren.
We chose the Differential AbilityScales (DAS) [Elliott, 1983], to assessgeneral cognitive ability in childrenbetween age 4 years and 17 years, 11months. The DAS cognitive batteryincludes three composite scores: theverbal cluster (VC) score measuressemantic knowledge, verbal expression,and verbal comprehension, the spatialcluster (SC) score measures nonverbalspatial cognitive ability, and the nonver-bal reasoning cluster score measuresnonverbal aspects of fluid reasoning.Performance on subtests was combinedto yield a general conceptual ability(GCA) score, which is a general indexof an individuals ability to performcomplex mental processing involvingconceptualization and manipulation ofinformation.
Academic achievement wasassessed with the Reading, Spelling, andArithmetic subtests from the WideRange Achievement Test-3 (WRAT3)[Wilkerson, 1993]. The tasks used toassess attention/executive functionincluded Conners Continuous Per-formance Test (CPT-II) [Connors,1995], Connors Kiddie CPT (age 45years) [Connors, 1995], and the Delis-Kaplin Executive Function System (D-KEFS) Color-Word Interference Test[Delis, 2001]. These tasks measure proc-essing speed, sustained attention,response inhibition, and inhibitory con-trol. We examined aspects of verbalmemory using the Childrens MemoryScale (CMS) [Cohen, 1997] for StoryRecall and Digit Span [Cohen, 1997],and California Verbal Learning Test-Childrens Version (CVLT-C) [Delis,1994]. We assessed visual-motor andvisual memory with the Rey-Osterrieth
Complex Figure-Copy and Organiza-tion scores [Waber and Holmes, 1985]and the Beery Test of Visual MotorIntegration [Beery, 1997].
Language ability was evaluated atthe level of single words with the Ex-pressive One-Word Vocabulary Test(EOWPVT) [Williams, 1997] and theReceptive One-Word Vocabulary Test(ROWPVT) [Brownell, 2000]. Phono-logical processing was assessed with theComprehensive Test of PhonologicalProcessing (CTOPP) [Rashotte, 1999],and fluency with the D-KEFS subtest,which tapped both phonemic andsemantic fluency [Korkman, 1998]. Weevaluated more complex levels of lan-guage processing with the Test of Lan-guage Competence-Expanded Edition[Wiig, 1989].
The tasks used to assess fine andgross motor skills included the LafayettePegboard [Klove, 1963], the Bruininks-Oseretsky Test of Motor Proficiency(BOT) [Bruininks, 1978] and Physicaland Neurological Evaluation for SoftSigns (PANESS) [Close, 1976].
Socioeconomic StatusSocioeconomic status (SES) esti-
mate was calculated for children usingthe Hollingshead 2-Factor Index ofSocial Status based on education andoccupation of parents [Hollingshead andRedlich, 1958].
Handedness and LateralizationThe Crovitz Laterality battery was
administered to document hand prefer-ences [Crovitz and Ziner, 1962]. Chil-dren were asked to demonstrate whichhand they use for eight activities (righthand 5 RH and left hand 5 LH). Alaterality quotient was calculated usingthe following formula: [(RH 2 LH)/(RH LH) 3 100]. Right-handednesswas defined as a score of 100% (per-formance of eight of eight tasks withthe RH). Non right-hand dominancewas characterized as a score
StatisticsResults are presented as the mean
6 SD of standard scores. Statisticalcomparisons performed includedANOVA comparing the three karyo-type groups for demographic, auxologicand cognitive measurements and ananalysis of covariance (ANCOVA) com-paring the three karotype groups,adjusting for pubic hair Tanner stage,head circumference SDS, testicular vol-ume SDS, lateralization index, andGCA from the DAS. The six pairwisecomparisons among the three karyotypegroups were performed using Scheffestest. P-values less than 0.05 were con-sidered to be statistically significant.Nominal P-values are reported andwere not adjusted for multiple compari-sons.
Genetic ResultsKaryotype results were as follows:
21 boys with XYY and 93 boys with47,XXY; no Mosaicism was detected.
DemographicsOur study included 21 boys with
XYY, age 4.314.4, 93 boys with KS,age 4.117.8 years, and 36 control boys,age 4.513.8 (Table 1). The groupswere well matched for age, SES, race,handedness, and for pubic hair Tannerstage development. Most participantswere Caucasian. The boys with XYYand XXY were, on average, taller thanthe control boys but had similar weightSDS. Testicular volume SDS was thelowest in the boys with KS (P 1SD) in 11/22 boys with XYY (age4.313.6 years), reflecting early pubertaldevelopment in some cases.
Diagnosis of XYY was made ininfancy in eight boys [six for prenatalscreening (advanced maternal age), onefor hypotonia, and one for other rea-sons], in childhood (age 212 years) in12 (two for language issues, three forbehavior issues, and seven for other
developmental reasons), and after age12 years in one boy (behavioral reasons).Of the 21 boys, 20 had received speechand/or reading therapy and 18 receivedoccupational and/or physical therapy bythe time of the evaluation. No boys withXYY were diagnosed with testicular fail-ure or had received testosterone treat-ment by the time of the evaluation.
Diagnosis of KS was made ininfancy in 61 boys [51 for prenatalscreening (advanced maternal age), onefor hypotonia, one for small genitalia,and eight for other reasons], in childhood(212 years) in 24 boys (seven for lan-guage issues, five for behavior issues, onefor tall stature, and 11 for other reasons),and after age 12 in 8 (two for languageissues and six for puberty issues). Of the93 boys, 83 had received special educa-tion services in school by the time of theevaluation: 75 received speech and/orreading therapy and 61 received occupa-tional and/or physical therapy. Twenty-one boys with KS had received testoster-one treatment by the time of the evalua-tion (duration of 0.12.2 years).
Table 1. Demographics and Auxologic Measurements (Mean 6 SD)
n XXY n XYY n Controls P a
Age 93 9.4 6 3.4 21 9.4 6 2.8 36 9.5 6 2.6 0.99SES 93 51 6 10 21 52 6 10 36 54 6 8 0.32Height SDS 93 0.9 6 1.2 21 0.9 6 1.1 36 0.1 6 1.0 0.001Weight SDS 93 0.6 6 1.2 21 0.6 6 1.2 36 0.4 6 1.2 0.65Head Circ SDS 93 0.4 6 1.6 21 1.2 6 2.3 36 0.9 6 1.4 0.08Tanner stage-pubic hair 93 1.6 6 1.1 20 1.3 6 0.9 34 1.3 6 0.8 0.18Testicular volume SDS (mean of 2) 92 21.3 6 1.5 20 2.7 6 4.1 34 1.0 6 2.6 0.0001Testosterone 87 55 6 111 21 47 6 92 Not done 0.66Race (%Caucasian) 93 85% 21 95% 36 78% 0.16
aANOVA, comparison of three groups.
Table 2. General Cognitive Ability and Achievement Results (Mean Standard Score 6 SD)
n XXY n XYY n Controls P a
DAS IndexVerbal cluster (VC) SS 92 89 6 14* 17 88 6 18** 35 113 6 14
Lateralization and HandednessBased on the Crovitz Handedness
Questionnaire, 63% (12/19) of theXYY group, 73% (68/93) of the KSgroup, and 72% (26/36) controls werecompletely right-handed (lateralityindex of 100%). The occurrence of nonright-handedness did not differ amongthe groups.
Cognitive ResultsResults from the DAS as well as
measures of language and academicachievement are presented in Table 2.GCA, the DAS indices and subtestsrevealed, on average, higher scores (by>1 SD) in the control group, comparedto the XYY and KS groups (P ) [KS]. In thisstudy, scores on the DAS GCA suggestthat general cognitive ability is mildlydiminished in both groups, comparedto controls. This general cognitive pro-file reflects not just decreased verbal,but also decreased nonverbal abilities inboth groups and diminished spatial abil-ity in the KS group. Importantly, afteradjusting for GCA differences betweenthe groups, the DAS VC in the XYYgroup still differed significantly from thecontrol group.
Language and AchievementMost previous studies have
described some features of language thatare impaired in both groups. Delayedspeech, impaired word retrieval, speedof linguistic processing, expressive, andreceptive capabilities and processing ofnarration have been described in boththe XYY and KS groups [Christensenand Nielsen, 1973; Ratcliffe et al.,1982; Walzer, 1985; Welch, 1985;Leonard and Sparrow, 1986]. Althoughthe pattern of impairment is similar inour results, the severity appears to dif-fer. The XYY group appears to have amore severe and pervasive languageimpairment than the KS group that ispresent at varying levels of complexityof oral and written language. We notedgreater impairment in the XYY versusthe KS group particularly for higher-level metalinguistic abilities, as demon-strated by significant difficulty in under-standing figurative language, interpret-ing ambiguities in language, as well asin oral expression and verbal memory.
This language impairment appearsto have important academic implica-tions. The boys with XYY, more thanKS, produced lower achievement inReading and Spelling, compared to thecontrol group. Our findings are similarto previous studies in XYY thatreported school difficulties out of pro-portion to what would be expected onthe basis of IQ. Boys with XYY andboys with KS commonly have difficulty
Table 5. Motor Function Results (Mean Standard Score 6 SD)
n XXY n XYY n Controls Pa
BOT CompositeFine motor composite SS 73 81 6 15* 8 81 6 22** 21 99 6 18
mastering school curricula and requirespecial education help in reading andwriting [Bender et al., 1984; Netley,1986; Ross et al., 2008].
Attention and Executive FunctionThis study shows that both the
XYY and KS groups had a similardegree of impairment relative to con-trols on attention and executive func-tion tasks, although cognitive flexibility,as exemplified by inhibition and switch-ing, was more impaired in the XYYthan the KS group. Both groups havebeen reported to have increased dis-tractibility [Walzer et al., 1990], and anincreased risk for hyperactivity andattention problems [Money et al., 1974;Theilgaard, 1984; Welch, 1985; Geertset al., 2003] [Ross et al., 2008]. Execu-tive dysfunction has been reported inadults with KS [Geschwind, 2000].
Visual Spatial FunctionPerformance results for visual-spa-
tial and visual-motor function were sig-nificantly lower in the KS but not theXYY group, compared to the controls.This dissociation may reflect testoster-one deficiency in the KS group only.Higher testosterone levels in males maybe related to increased male perform-ance in visual-spatial tasks involvingmental rotation, spatial perception, spa-tial visualization [Arceneaux et al.,1996].
Motor FunctionSimilar to previous observations,
both the XYY and the KS groups hadimpairment of motor function [Salben-blatt et al., 1987; Bender et al., 1993;Ross et al., 2008]. However, the KSgroup appeared to have more pervasivemotor impairment than the XYYgroup. Motor function was examinedusing fine motor and gross motor tasksas well as measures of strength, speedand agility, and coordination. On por-tions of the PANESS, including repeti-tive thumb finger tapping and foottapping, the XYY and KS groups per-formed at or close to levels expected forage, similar to previous results [Salben-blatt et al., 1987; Bender et al., 1993].However, as the tasks became morecomplex (tapping four sequential fingersto thumb), both groups did not per-form as well as controls. The morecomplex tasks require greater utilizationof coordination and attention, whichare impaired in both groups. Bothgroups also performed less well thanexpected for their age on the Strengthand the Upper limb speed and dexterity
subtests. These motor difficulties are notjust of academic interest but have im-portance for these boys because of psy-chosocial implications and the likelyimpaired athletic ability that accompa-nies these particular deficits. Perform-ance by the KS group was lower thanthe XYY group on the test of RunningSpeed and Agility from the BOT,which indexes an array of motor andcognitive skills. This may be due toandrogen deficiency having a negativeimpact in only the KS group and notthe XYY group.
SUMMARY AND CONCLUSIONSIn general, the cognitive pheno-
type in boys with XYY and KS overlapwith some important differences. Bothhave mild generalized cognitive impair-ment, with impaired language verbalmemory, attention, visual-motor, and
motor function. The similarity of cog-nitive findings in these two genetic dis-orders of males may be related to over-lapping gene dosage abnormalities. TheX and Y chromosomes share identicalsequences in the pseudoautosomalregion (PAR1), a 2.6 Mb interval at thetips of Xp and Yp, and genes areequally expressed from the X or YPAR1 [Rappold, 1993; Vaknin et al.,2008]. Specifically, tall stature in both ofthese populations is thought to be dueto increased expression from threeinstead of two copies of the heightdetermining SHOX gene [Rao et al.,1997; Aksglaede et al., 2008].
The differences between cognitivephenotypes in the KS and XYY groupsmay be related to either chromosomalor hormonal causes. The results showthat XYY boys have a more profoundlanguage impairment and the KS boyshave a more profound motor impair-ment. We hypothesize that the moresevere language-based cognitive pheno-type in XYY versus KS is likely to be
genetically determined on the basis ofabnormal dosage of specific Y chromo-some genes, but not abnormal levels oftestosterone because XYY is not associ-ated with testicular failure. The parentalorigin of the extra chromosome maydifferentially impact KS and XYYbecause in KS, the supernumerary Xchromosome may be maternal or pater-nal, whereas in males with XYY, theextra Y chromosome always originatesfrom the father. Hormonal differences(normal testosterone in XYY versus tes-tosterone deficiency in KS) mayaccount for differences in the cognitivephenotype in boys with XYY versusXXY. The testosterone deficiency inKS and the known relationship betweenmuscle function and testosterone mayalso account for some of the motorimpairment in this group.
Another potential factor relatedto the observed difference in the XYYand KS groups relates to their ascertain-ment. In our cohort, most of the boyswith XYY were diagnosed postnatallyon the basis of behavior/developmentalissues, consistent with the observationthat diagnosis of XYY is often delayed[Fryns et al., 1995; Abramsky andChapple, 1997; Geerts et al., 2003]. Incontrast, most of the KS boys in ourcohort were diagnosed prenatally on thebasis of advanced maternal age. Thus,there may be a bias in our cohorttowards greater severity among theXYY boys. However, boys with XYYascertained from screening studies ofmale newborns for sex chromosomeabnormalities also have characteristicspeech, language-based, motor, andbehavior findings [Bender et al., 1984;Salbenblatt et al., 1987; Bender et al.,1993], suggesting that their findings areassociated with the karyotype, inde-pendent of ascertainment.
The results from these large XYYand KS cohorts have important neuro-cognitive and educational implications.From the neurocognitive standpoint,the difficulties present represent an op-portunity to gain insights into brain de-velopment and the interactions of cog-nitive systems in boys with XYY or KS.From the educational standpoint, thedifficulty in complex language process-ing and impaired attention as well asmotor function identified in the XYYand KS populations may be missed.This can be a challenge to educators. Itis critical that boys with XYY and boyswith KS are provided with appropriateeducational interventions that targettheir learning challenges in school.These findings would also be an impor-
The XYY group appearsto have a more severe and
pervasive languageimpairment than the KSgroup that is present at
varying levels ofcomplexity of oral andwritten language.
Dev Disabil Res Rev Cognition in Boys with XYY or Klinefelter Syndrome Ross et al. 315
tant component of counseling cliniciansand families about these disorders. n
ACKNOWLEDGMENTSThe authors thank the families
who participated in these studies.
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