510 ArchivesofDiseasein Childhood 1993; 68: 510-512

CURRENT TOPIC Arch Dis Child: first published as 10.1136/adc.68.4.510 on 1 April 1993. Downloaded from Developmental dyscalculia, gender, and the brain

Varda Gross-Tsur, Orly Manor, Ruth S Shalev

Background Aldenkamp reported that children in the 12-18 Developmental dyscalculia is a primary cognitive year age group had the most difficulties with disorder of childhood affecting the ability of an mathematics. 14 Seidenberg et al studied the otherwise intelligent and healthy child to learn academic achievement of 122 children ages 7-15 arithmetic.' Preliminary evidence indicates that years and found that this group was making less developmental dyscalculia is seen in 5-6% of academic progress than expected for their age normal children23 and is as prevalent as develop- and level of intelligence quotient (IQ); academic mental dyslexia or the attention deficit hyper- deficiencies were greatest in the area of arith- activity disorder.' One of the classifications of metic followed by spelling, reading comprehen- developmental dyscalculia subdivides dys- sion, and word recognition skills.'5 It has been calculia to: (1) alexia and agraphia for numbers, postulated that the 'speed factor type' oflearning (2) spatial dyscalculia, (3) anarithmetia (impair- disability in epileptic children was found to be ment of calculation per se), (4) attentional- related to underachievement in arithmetic.8 sequential dyscalculia, and (5) mixed type.4 Early age of seizure onset, age of the child, Rourke and Finlayson used associated learning increased lifetime total seizures, and the pres- disabilities as a basis for their two group classifi- ence of multiple seizure types (especially tonic- cation of dyscalculia: (1) reading, writing, and clonic and absence) were associated with poor arithmetic equally impaired and (2) impaired arithmetic achievement scores.'5 The mecha- arithmetic but reading and writing average or nisms by which epilepsy may interfere with above.5 Kosc, however, emphasised the brain learning ability are multifactorial and include based nature of dyscalculia and defined it as 'a many of these same factors, for example the type structural disorder which has its origin in a (generalised seizures more than partial seizures) genetic or congenital disorder of those parts and number of seizures, the clinical syndrome of the brain that are the direct anatomico- involved, age of seizure onset, subclinical physiological substrate of the maturation of the epileptiform activity, and the effect of anti- http://adc.bmj.com/ mathematical abilities'.2 epileptic drugs.8 16 Underachievement in arithmetic is also seen in Another syndrome in which dyscalculia children with low intellectual ability,6 adverse appears is phenylketonuria, an inborn error of psychological factors, and low socioeconomic metabolism in which the fundamental defect is status3'7 as well as in children with neurological the absence of phenylalanine hydroxylase. disorders. In fact, developmental dyscalculia is Dietary manipulation prevents mental retarda- the most frequently encountered learning dis- tion in most cases but these children still have a on September 25, 2021 by guest. Protected copyright. ability in children with epilepsy,8 fragile X raised rate of cognitive and behavioural prob- carriers, Turner's syndrome, and phenyl- lems. Their learning profile is characterised by ketonuria.9 It is also a major symptom in difficulties in mathematics and symptoms of the developmental disorders of childhood such as attention deficit hyperactivity disorder. Read- the attention deficit hyperactivity syndrome,'0 ing is acquired normally. Dietary control may the developmental Gerstmann's syndrome," and affect cognition perhaps by alteration of the developmental right hemisphere syndrome. 12 dopamine concentrations.9 Moreover, there appears to be an unusually high prevalence ofdevelopmental dyscalculia in girls. In this article we will focus on the neurological Developmental dyscalculia and developmental and developmental disorders associated with disorders dyscalculia and discuss evidence for the apparent Attention deficit hyperactivity disorder is Neuropediatric Unit, sex difference in its occurrence. defined as a disorder ofinappropriateinattentive- Shaare Zedek Medical Center, Jerusalem, Israel ness, impulsivity, and hyperactivity,' and is Varda Gross-Tsur diagnosed in clinical practice when a sufficient Ruth S Shalev Developmental dyscalculia and neurological number ofdescriptors listed in theDiagnostic and disorders Statistical Manual Mental Braun School ofHealth of Disorders Third and Community One neurological disorder that carries an undue Edition, Revised criteria fit the patients. This Medicine, Hadassah risk of developing dyscalculia is epilepsy. disorder is frequently encountered in the normal University Hospital, Epileptic children have a high incidence of population and these children are likely to Jerusalem, Israel Orly Manor academic underachievement. At least one third experience difficulty in arithmetic, even if they Correspondence to: ofepileptic children receive some form of educa- acquire reading and spelling skills at an age Dr Varda Gross-Tsur, tional support during their school careers.8 appropriate pace.'0 As there are no biological Neuropediatric Unit, Shaare Zedek Medical Center, POB Several studies reported that the academic skill markers for the condition, Shaywitz and 3235, Jerusalem, Israel 91031. most impaired in these children is arithmetic.'3 Shaywitz utilised the depressed scores on four Developmental dyscalculia, gender, and the brain 511

Wechsler intelligence scale for children - revised nation of low arithmetic, digit span, and block (WISC-R) subtests: arithmetic, coding, infor- design subtest scores on the WISC-R.2' More mation, and digit span as a supplementary detailed neuropsychological testing demon- diagnostic test.'7 Arithmetic underachievement, strated visuospatial dysfunction and behavioural Arch Dis Child: first published as 10.1136/adc.68.4.510 on 1 April 1993. Downloaded from in their opinion, is part of the definition of most and emotional problems that were all suggestive children with attention deficit hyperactivity dis- of a right hemisphere developmental impair- order. Thus it is not surprising that children who ment. The authors speculate that the presence of underachieve in mathematics are characterised the fragile X gene causes a specific set of focal by attention deficits and perceptual motor prob- deficits with a spectrum of clinical involvement. lems.'8 Furthermore up to 50-80% of children Turner's syndrome, a chromosomal aneuploidy with attention deficit hyperactivity disorder have of 45X, consists of small stature, gonadal dys- learning disabilities, including dyscalculia. ' genesis, transient congenital lymphoedema, and Another brain developmental disorder in dysmorphic features. Girls with this syndrome which developmental dyscalculia is one of the have problems in arithmetic and handwriting. major characteristics is the right hemisphere These girls do better on verbal tests relative syndrome. Weintraub and Mesulam described a to their achievement on performance and group of patients with a behavioural syndrome numerical tests. Right parietal lobe dysfunction, beginning in early life, characterised by possibly related to the basic chromosome defect, emotional and interpersonal difficulties, visuo- is postulated as the cause ofthe cognitive impair- spatial disturbances, inadequate paralinguistic ment.22 Boys, on the other hand, with sex communication, and neurological evidence of chromosome aneuploidies have increased risk right hemisphere dysfunction. 12 In their patients for reading disabilities.9 dyscalculia was demonstrated in those with Whereas developmental dyslexia and atten- average intellectual capacity and non-dyslexic tion deficit hyperactivity disorder are more learning disabilities. Other children with right prevalent in boys with a ratio of 3-6:1,' develop- hemisphere syndrome showed a profound mental dyscalculia seems to affect both sexes inability to conceptualise numerical quantities, more equally.2324 Arithmetic testing on 100 while symbol recognition and production were normal boys and 99 normal girls did not demon- both preserved.' Weintraub and Mesulam sug- strate differences in gender between the lower gested that acquisition of number concepts scoring children (lower 10% of sample) and the requires the participation of neural mechanisms rest ofthe group.25 In the reports on the develop- of both hemispheres and may also be disrupted mental right hemisphere syndrome there were by early right hemisphere dysfunction.'2 Using equal or greater numbers of women than average evoked potentials during a neurometric men.'226 These sex differences in learning dis- battery (psychometric tests developed to avoid abilities are most apparent in the extreme cases of linguistic and cultural constraints), John et al sex anomalies, such as Turner's syndrome or the were able to show that children with isolated supernumerary X syndromes. Speculations con- arithmetic underachievement had specific and cerning sex differences in brain organisation and http://adc.bmj.com/ consistent F ratio patterns in the 300-500 msec cognitive function resulting from hormonal latency domain on the right hemisphere, differ- influences on prenatal guidance of neuronal ing significantly from patterns of children with migration and neuronal connections have been other learning disabilities or normal subjects.`0 entertained.2728 Geschwind and Galaburda sug- Evidence has also been presented for visuospatial gested that gonadal hormones, especially test- dysfunction as one of the prerequisites for estorone, may influence the development of

developmental dyscalculia.I anomalous brain dominance and favour talents on September 25, 2021 by guest. Protected copyright. Developmental dyscalculia is a major criterion associated with superior development of certain necessary to diagnose the developmental regions in the right hemisphere.27 Such hor- Gerstmann's syndrome, the others being finger monal influences could impact on future acquisi- agnosia, right-left disorientation, and dys- tion of arithmetic skills in normal boys and girls graphia." The neurophysiological substrate is and have important determining effects for thought to be localised to the left inferior parietal developmental dyscalculia. lobe. Kinsbourne and Warrington reported The data regarding hemispheric lesions in seven children with developmental Gerstmann's children and mathematical abilities is contradic- syndrome and emphasised the profundity of tory. Whereas dyscalculia was noted as the only their arithmetical difficulties." Three of their major neuropsychological deficit associated with cases were not able to do simple additions despite impaired language in left hemisphere lesioned good comprehension ofnumber concepts. children, arithmetic achievement has been cor- related with lack of right hemisphere impair- ment. In another study, arithmetic impairment Developmental dyscalculia and gender was not a discriminatory factor between left or Whereas isolated learning disabilities other than right hemisphere lesioned children." However, developmental dyscalculia are more common in developmental dyscalculia is a major symptom of boys,' developmental dyscalculia is more preva- developmental right hemisphere syndromes lent in girls with epilepsy, sex chromosome and others in which visuospatial functions aneuploidies, and in female carriers offragile X.9 are impaired, for example Turner's syndrome, The carriers of fragile X, heterogenous for the fragile X carriers, etc. fragile site, demonstrate a broad spectrum of If developmental dyscalculia is the result of behavioural and cognitive dysfunction.9 Kemper developmental hemispheric dysfunction, one etal reported a specific cognitive profile in female could speculate that the 'cognitive crowding' carriers of fragile X with a characteristic combi- phenomenon might explain the genesis of the 512 Gross-Tsur, Manor, Shalev

' the development of function: a neuropsychological approach. 2nd Ed. New York: symptomatology. Thus, Springer, 1985: 355-69. language in the right hemisphere would take 7 O'Hare AE, Brown JK, Aitken K. Dyscalculia in children. other skills Dev Med Child Neurol 1991; 33: 356-61. priority over acquisition of cognitive 8 Aldenkamp AP, Alpherts WCJ, Dekker MJA, Overweg 1. specific to this hemisphere including arithmetic Neurophsyclological aspects of learning disabilities in Arch Dis Child: first published as 10.1136/adc.68.4.510 on 1 April 1993. Downloaded from that could explain epilepsy. Epilepsia 1990; 31 (suppl 4): S9-20. function. Another hypothesis 9 Pennington BF. Genetics oflearning disabilities. Semin Neurol the selective development of developmental dys- 1991; 11:28-34. 10 Ackerman PT, Anhalt JM, Dykman RA. 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