Ruth S. Shalev

DEVELOPMENTAL DYSCALCULIA: PREVALENCE AND DEMOGRAPHIC FEATURES

One hundred and forty‐thrée 11‐year‐old children with developmental dyscalculia, from a cohort of 3029 students, were studied to determine demographic features and prevalence of this primary cognitive disorder. They were evaluated for gender, IQ, linguistic and perceptual skills, symptoms of attention‐deficit hyperactivity disorder (ADHD), socio‐economic status and associated learning disabilities. The IQs of the 140 children (75 girls and 65 boys) retained in the study group (thrée were excluded because of low IQs) ranged from 80 to 129 (mean 98.2, SD 9.9). 26 per cent of the children had symptoms of ADHD, and 17 per cent had dyslexia. Their socio‐economic status was significantly lower than that of the rest of the cohort, and 42 per cent had first‐degrée relatives with learning disabilities. The prevalence of dyscalculia in the original cohort was 6.5 per cent, similar to that of dyslexia and ADHD. However, unlike these other learning disabilities, dyscalculia affected the two sexes in about the same proportions.

Number development and developmental dyscalculia

There is a growing consensus that the neuropsychological underpinnings of developmental dyscalculia (DD) are a genetically determined disorder of ‘number sense’, a term denoting the ability to represent and manipulate numerical magnitude nonverbally on an internal number line. However, this spatially‐oriented number line develops during elementary school and requires additional cognitive components including working memory and number symbolization (language). Thus, there may be children with familial‐genetic DD with deficits limited to number sense and others with DD and comorbidities such as language delay, dyslexia, or attention‐deficit‐hyperactivity disorder. This duality is supported by epidemiological data indicating that two‐thirds of children with DD have comorbid conditions while one‐third have pure DD. Clinically, they differ according to their profile of arithmetic difficulties. fMRI studies indicate that parietal areas (important for number functions), and frontal regions (dominant for executive working memory and attention functions), are under‐activated in children with DD. A four‐step developmental model that allows prediction of different pathways for DD is presented. The core‐system representation of numerical magnitude (cardinality; step 1) provides the meaning of ‘number’, a precondition to acquiring linguistic (step 2), and Arabic (step 3) number symbols, while a growing working memory enables neuroplastic development of an expanding mental number line during school years (step 4). Therapeutic and educational interventions can be drawn from this model.

Developmental dyscalculia : prevalence and prognosis

The prevalence of developmental dyscalculia (DC) in the school population ranges from 3–6%, a frequency similar to that of developmental dyslexia and ADHD. These studies fulfilled the criteria for an adequate prevalence study, i.e., were population based, using standardized measures to evaluate arithmetic function. Although the variation in prevalence is within a narrow range, the differences are probably due to which definition of dyscalculia was used, the age the diagnosis was made and the instrument chosen to test for DC. The relative predominance of girls with DC may reflect a greater vulnerability to environmental influences alone or in addition to a biological predisposition. DC is not only encountered as a specific learning disability but also in diverse neurological disorders, examples of which include ADHD, developmental language disorder, epilepsy, treated phenylketonuria and Fragile X syndrome. Although the long-term prognosis of DC is as yet unknown, current data indicate that DC is a stable learning disability persisting, at least for the short term, in about half of affected children. The long-term consequences of DC and its impact on education, employment and psychological well-being have yet to be determined.

Developmental dyscalculia: a prospective six-year follow-up

To determine the natural history of developmental dyscalculia (DC) and factors impacting on its prognosis, we performed a prospective six-year longitudinal study. One hundred and forty children of normal intelligence diagnosed with DC in the fifth grade of elementary school were re-examined for dyscalculia three and six years later, in eighth (n=123) and eleventh (n=104; 41 males, 63 females) grades respectively. Mean age of the children in fifth grade was 11 years 1 month (SD 4 months), in eighth grade 14 years 2 months (SD 1 month), and in eleventh grade 17 years 2 months (SD 5 months). The assessment included standardized arithmetic, reading and writing tests, behavioural rating scales, information on socioeconomic status, educational interventions, and familial learning problems. Participants in eleventh grade were recategorized as having DC if their score on the arithmetic test was not more than the fifth centile for grade. At the six-year follow-up, 99/104 (95%) children diagnosed with dyscalculia in fifth grade were still performing poorly in arithmetic, scoring within the lowest quartile for their grade, and 42/104 (40%) were recategorized with DC. Chronicity of DC was associated with severity of the dyscalculia in fifth grade (p<0.05), lower IQ (p<0.01), inattention (p<0.01), and writing problems (p<0.01). Thus, DC is an enduring specific learning difficulty, persisting into late adolescence in almost half of affected individuals.

Developmental Right-Hemisphere Syndrome Clinical Spectrum of the Nonverbal Learning Disability

We report the clinical characteristics of the developmental right-hemisphere syndrome (DRHS), a nonverbal learning disability, in 20 children (9 girls and 11 boys; mean age = 9.5 years) who also manifested attention-deficit/hyperactivity disorder (ADHD), severe graphomotor problems, and marked slowness of performance. Diagnostic criteria for this study included (a) emotional and interpersonal difficulties; (b) paralinguistic communication problems; (c) impaired visuospatial skills, verbal IQ > performance IQ, and verbal IQ · 85; and either (d) dyscalculia or (e) neurological signs on the left side of the body. In this group, verbal IQ was significantly higher than performance IQ (106.6 · 13.0 vs. 85.1 · 13.1, respectively, p < .01). Arithmetic was the lowest score among the verbal subtests (7.8 · 3.5, p < .01) and Geometrical Design was the lowest score among the performance subtests (5.8 · 1.7). Thirteen children had soft neurological signs on the left side of the body. ADHD was seen in all 20 children, marked slowness of performance in 16, and severe graphomotor problems in 18. The latter two features have not been previously described as part of DRHS.

Developmental Dyscalculia Is a Familial Learning Disability

Whereas current evidence attests to a genetic component in the etiology of dyslexia and attention-deficit/hyperactivity disorder (ADHD), little is known about the role of genetics in developmental dyscalculia (DC). The objective of this study was to determine the familial aggregation of DC. Siblings and parents of children with DC were assessed for arithmetic, reading and attention disorders. The criteria for DC were an IQ higher than 85, poor performance in arithmetic, and a significant discrepancy between arithmetic achievement and IQ. The study group was composed of 39 children with DC, 21 mothers, 22 fathers, 90 siblings, and 16 second-degree relatives. We found that 66% of mothers, 40% of fathers, 53% of siblings, and 44% of second-degree relatives had DC. The intraclass correlation between the sib pairs was .27. A 95% confidential interval (CI) for the prevalence of DC among siblings of DC probands (see Note 1) ranged from 40% to 64%, indicating a familial prevalence almost tenfold higher than expected for the general population. IQ and attention problems were not risk factors for DC. We conclude that DC, like other learning disabilities, has a significant familial aggregation, suggesting a role for genetics in the evolution of this disorder.

Syndrome dimensions of the Child Behavior Checklist and the Teacher Report Form : A critical empirical evaluation

The construct representation of the cross-informant model of the Child Behavior Checklist (CBCL) and the Teacher Report Form (TRF) was evaluated using confirmatory factor analysis. Samples were collected in seven different countries. The results are based on 13,226 parent ratings and 8893 teacher ratings. The adequacy of fit for the cross-informant model was established on the basis of three approaches: conventional rules of fit, simulation, and comparison with other models. The results indicated that the cross-informant model fits these data poorly. These results were consistent across countries, informants, and both clinical and population samples. Since inadequate empirical support for the cross-informant syndromes and their differentiation was found, the construct validity of these syndrome dimensions is questioned.

ADHD and Dysgraphia: Underlying Mechanisms

Multiple complaints in the domain of writing are common among children with Attention Deficit Hyperactivity Disorder (ADHD). In this work we sought to characterize the writing disorder by studying dysgraphia in twenty 6th grade boys with ADHD and normal reading skills matched to 20 healthy boys who served as a comparison group. Dysgraphia, defined as deficits in spelling and handwriting, was assessed according to neuropsychological explanatory processes within 3 primary domains: linguistic processing, motor programming and motor kinematics. Children with ADHD made significantly more spelling errors, but showed a unique pattern introducing letter insertions, substitutions, transpositions and omissions. This error type, also known as graphemic buffer errors, can be explained by impaired attention aspects needed for motor planning. Kinematic manifestations of writing deficits were fast, inaccurate and an inefficient written product accompanied by higher levels of axial pen pressure. These results suggest that the spelling errors and writing deficits seen in children with ADHD and normal reading skills stem primarily from non-linguistic deficits, while linguistic factors play a secondary role. Recommendations for remediation include educational interventions, use of word processing and judicious use of psychostimulants.

Visual impairment in children with epilepsy treated with vigabatrin

Vigabatrin is an anti‐epileptic drug particularly useful for drug‐resistant partial seizures and infantile spasms. Recently, vigabatrin‐induced visual field constriction (VFC) and abnormal ocular electrophysiological studies were reported. In this study, we assessed visual fields, visual evoked potentials (VEPs), and electroretinography (ERG) in children treated with vigabatrin. Twenty‐four visually asymptomatic children underwent a clinical ophthalmological examination, perimetry when appropriate, and VEP and ERG. Thirteen patients had at least one abnormal study. VFC was seen in 11 of 17 patients who had perimetry; 5 of 15 patients who underwent VEP testing and 4 of 11 who underwent ERG testing had abnormal examinations. For the most part, abnormal VEPs and ERGs were found in children who also had VFC. There was a consistent trend for longer treatment periods to correlate with VFC, abnormal ERGs, and VEPs. In summary, over half of the children treated with vigabatrin demonstrated VFC or abnormal ocular electrophysiological studies. Perimetry seemed to be the most sensitive modality for identifying vigabatrin toxicity. Abnormal ERGs and VEPs were primarily seen in children with VFC and may be useful in monitoring children who are not appropriate candidates for perimetry. Although the incidence of vigabatrin‐induced VFC is worrisome, in the context of intractable seizures or infantile spasms, therapeutic benefits must be weighed against risks. Ann Neurol 2000;48:60–64

Glutaric aciduria type I Clinical heterogeneity and neuroradiologic features

We present four patients, two pairs of siblings, with glutaric aciduria type I (GA I). All four had undetectable glutaryl-CoA dehydrogenase activity on fibroblast culture and massive urinary excretion of glutaric acid. All had serum carnitine deficiency at time of diagnosis except one patient who was diagnosed neonatally. All had a unique pattern of frontotemporal atrophy on CT. Remarkably, in both sibling pairs, one child was asymptomatic. This suggests that the biochemical markers hitherto identified with GA I do not encompass the entire scope of the metabolic or enzymatic abnormalities. Alternatively, as yet unidentified mechanisms might spare or delay the destructive process.