Dyslexia in adults is associated with clinical signs of fatty acid deficiency

If waking and dreaming consciousness became de-differentiated, would schizophrenia result?

If both waking and dreaming consciousness are functional, their de-differentiation would be doubly detrimental. Differentiation between waking and dreaming is achieved through neuromodulation. During dreaming, without external sensory data and with mesolimbic dopaminergic input, hyper-cholinergic input almost totally suppresses the aminergic system. During waking, with sensory gates open, aminergic modulation inhibits cholinergic and mesocortical dopaminergic suppresses mesolimbic. These neuromodulatory systems are reciprocally interactive and self-organizing. As a consequence of neuromodulatory reciprocity, phenomenologically, the self and the world that appear during dreaming differ from those that emerge during waking. As a result of self-organizing, the self and the world in both states are integrated. Some loss of self-organization would precipitate a degree of de-differentiation between waking and dreaming, resulting in a hybrid state which would be expressed heterogeneously, both neurobiologically and phenomenologically. As a consequence of progressive de-differentiation, certain identifiable psychiatric disorders may emerge. Ultimately, schizophrenia, a disorganized-fragmented self, may result.

The association of fatty acid deficiency symptoms (FADS) with actual essential fatty acid status in cheek cells

Seven clinical symptoms have been utilised in several studies as a means of potentially identifying children with a deficiency in essential polyunsaturated fatty acids (PUFAs). The purpose of this study was to investigate whether there was any correlation between parental reports of the frequency of these seven 'fatty acid deficiency symptoms' (FADS) with actual levels of fatty acids in buccal cell samples of 450 children aged 8-10 years old. Additionally, the relationship between FADS and cognitive test performance, ratings of attention and behaviour and other somatic complaints were explored. The severity of reported FADS was not related to the levels of omega-6 or omega-3 in buccal cell samples. There was a relationship between parental reports of child behaviour and reported FADS; with high FADS being related to higher ratings of behaviour problems. Using FADS as a marker of PUFA deficiency may not be appropriate especially when assessing typically developing children.

Genetics of developmental dyslexia

Developmental dyslexia is a highly heritable disorder with a prevalence of at least 5% in school-aged children. Linkage studies have identified numerous loci throughout the genome that are likely to harbour candidate dyslexia susceptibility genes. Association studies and the refinement of chromosomal translocation break points in individuals with dyslexia have resulted in the discovery of candidate genes at some of these loci. A key function of many of these genes is their involvement in neuronal migration. This complements anatomical abnormalities discovered in dyslexic brains, such as ectopias, that may be the result of irregular neuronal migration.

Oiling the brain: a review of randomized controlled trials of omega-3 fatty acids in psychopathology across the lifespan

Around one in four people suffer from mental illness at some stage in their lifetime. There is increasing awareness of the importance of nutrition, particularly omega-3 polyunsaturated fatty acids (n-3 PUFA), for optimal brain development and function. Hence in recent decades, researchers have explored effects of n-3 PUFA on mental health problems over the lifespan, from developmental disorders in childhood, to depression, aggression, and schizophrenia in adulthood, and cognitive decline, dementia and Alzheimer's disease in late adulthood. This review provides an updated overview of the published and the registered clinical trials that investigate effects of n-3 PUFA supplementation on mental health and behavior, highlighting methodological differences and issues.

Adult Dyslexia and Attention Deficit Disorder in Finland--Project DyAdd: WAIS-III cognitive profiles

The project Adult Dyslexia and Attention Deficit Disorder in Finland (Project DyAdd) compares adults (n = 119, 18-55 years) with dyslexia, attention-deficit/hyperactivity disorder (ADHD), dyslexia together with ADHD (comorbid), and healthy controls with neuropsychological, psychophysical, and biological methods. The focus of this article is on the Wechsler Adult Intelligence Scale-Third Edition (WAIS-III). The clinical groups performed well compared to the norms, and they did not differ from each other. However, compared to the controls, all of them were slightly poorer in their Full IQ, and of the factors, processing speed was relatively difficult for all of them. In addition to the group comparisons, a cluster analysis based on subtest scores was conducted over the clinical groups. It did not suggest a solution that would differentiate between the clinical groups. Instead, four clusters emerged: above average, average, poor perceptual organization, and poor working memory. Thus, differentiating between these clinical groups with the WAIS-III was not possible. However, all of them shared a relative difficulty in processing speed, and group-independent clusters with perceptual or memory difficulties emerged.

A meta-analysis of blood fatty acids in people with learning disorders with particular interest in arachidonic acid

Small individual studies report that people with learning disorders have lower than normal blood concentrations of docosahexaenoic acid and arachidonic acid. The origin and consequence of the subnormal docosahexaenoic acid have been much speculated. However, relatively little attention has been paid to the significance of the low arachidonic acid concentration. Studies were identified through a literature search including subjects with various learning disorders or symptoms thereof and age-matched controls. A meta-analysis of pooled data from the red blood cell and plasma/serum showed that red blood cell arachidonic acid and docosahexanoic acid concentrations were significantly lower than normal [-3.93 and -18.92, respectively (weighted mean difference as a % of weighted mean control)]. Plasma/serum arachidonic acid and docosahexaenoic acid concentrations were also significantly lower than normal [-6.99 and -15.66, respectively (weighted mean difference as a % of weighted mean control)]. However, in absolute amounts the arachidonic acid was as severely depressed as docosahexanoic acid within red blood cells 0.57mg/100mg of fatty acid below normal verses 0.59mg/100mg for docosahexaenoic acid. Plasma/serum arachidonic acid was even lower; 0.71mg/100mg of fatty acid below normal verses 0.34mg/100mg for docosahexaenoic acid. The origin, consequences and relative importance of subnormal arachidonic acid to brain function bears further investigation.

Project DyAdd: Fatty acids and cognition in adults with dyslexia, ADHD, or both

Both attention deficit hyperactivity disorder (ADHD) and dyslexia are suggested to co-occur with altered fatty acid (FA) metabolism, but it is unknown how FAs are associated with the cognitive domains that characterize these disorders. In the project DyAdd, we investigated the associations between FAs in serum phospholipids and phonological processing, reading, spelling, arithmetic, executive functions, and attention. Healthy controls (n=36), adults with ADHD (n=26), dyslexia (n=36), or both (n=9) were included in the study. FAs included saturated, monounsaturated, total polyunsaturated, n-3, and n-6 FAs, together with n-6/n-3, AA/EPA, and LA/ALA ratios. When all the study subjects were included in the analyses, especially polyunsaturated FAs (PUFAs) were positively associated with cognition, but reading was least associated with FAs. These associations were modulated by gender, intelligence, n-3 PUFA intake, and group. Accordingly, within the ADHD group, only few associations emerged with PUFAs, n-6 PUFAs, and cognitive domains, whereas in the dyslexia group the more prevalent associations appeared with PUFAs and n-3 PUFAs.

Project DyAdd: Fatty acids in adult dyslexia, ADHD, and their comorbid combination

In project DyAdd, we compared the fatty acid (FA) profiles of serum phospholipids in adults with attention deficit hyperactivity disorder (ADHD) (n=26), dyslexia (n=36), their comorbid combination (n=9), and healthy controls (n=36). FA proportions were analyzed in a 2x2 design with Bonferroni corrected post hoc comparisons. A questionnaire was used to assess dietary fat quality and use of supplements. Results showed that ADHD and dyslexia were not associated with total saturated FAs, monounsaturated FAs, or n-3 polyunsaturated FAs (PUFAs). However, those with ADHD had elevated proportions of total n-6 PUFAs (including gamma-linolenic and adrenic acids) as compared to those without ADHD. Dyslexia was related to a higher proportion of monounsaturated nervonic acid and a higher ratio of n-6/n-3 PUFAs. Among females none of the associations were significant. However in males, all the original associations observed in all subjects remained and ADHD was associated with elevated nervonic acid and n-6/n-3 PUFA ratio like dyslexia. Controlling for poorly diagnosed reading difficulties, education, dietary fat quality, or use of FA supplements did not generally remove the originally observed associations.

Niacin skin test response in dyslexia

The niacin skin test reflects a flush and oedema owing to the production of prostaglandin D2 from arachidonic acid. A diminished response may indicate abnormalities in the phospholipid metabolism, which has been shown in schizophrenia. There is evidence that dyslexia might also involve phospholipid abnormalities, therefore we examined the skin response in 51 dyslexics and 45 controls. Four concentrations of aqueous methyl nicotinate were applied topically to the forearm. Flushing was rated using a seven-point scale at 3 min intervals over 21 min. Repeated measures ANOVA for the four concentrations across all seven time-points showed no significant effect of subject group, but when analyses were confined to the first 9 min, flushing was reduced in dyslexics. Significant group differences were also found for the lowest niacin concentration (0.0001M) across six out of seven time-points. The results indicate a slightly reduced and delayed response to niacin in dyslexia.

The role of dietary fatty acids in children's behaviour and learning

A growing awareness and understanding of the profiles of local children in County Durham, UK, experiencing learning and behavioural difficulties throughout the education system, has resulted in a number of school based nutritional intervention studies being undertaken. Evidence suggests that some children and young adults with developmental difficulties have a deficiency of particular omega 3 and omega 6 polyunsaturated fatty acids and supplementation with these nutrients can have an impact on their behaviour, concentration and performance on standardised assessments. The first randomised placebo controlled trial to be carried out on children in Durham with developmental coordination disorder has demonstrated significant effects of fatty acid supplementation on behaviour, reading and spelling performance. We are conducting further scientific studies within Durham and neighbouring Authorities in the North of England to be published at a future time. We have also carried out a number of open label treatment studies within schools to help us understand better the role that nutritional intervention can play across a broader range of age groups and abilities. The results suggest positive outcomes for a substantial proportion of children who are more able to engage with the educational opportunities presented to them. This is an important finding to be shared with educationalists, health professionals and importantly the parents.

Membrane fatty acids, reading and spelling in dyslexic and non-dyslexic adults

Increasing evidence implicates functional deficiencies or imbalances of omega-3 and omega-6 fatty acids in dyslexia. The associations between literacy skills and omega-3 and omega-6 fatty acid status were examined. 32 dyslexics and 20 controls completed standardised tests of reading and spelling and gave venous blood samples for analysis of the polar lipid fatty acid composition of red blood cell (RBC) membranes. Relationships between literacy skills and omega-3 and omega-6 concentrations were examined using rank-order correlations. Better word reading was associated with higher total omega-3 concentrations in both dyslexic and control groups. In dyslexic subjects only, reading performance was negatively associated with the ratio of arachidonic acid/eicosapentaenoic acid (ARA/EPA) and with total omega-6 concentrations. There were no significant differences in membrane fatty acid levels between the dyslexic and control subjects. However, the finding that omega-3 status was directly related to reading performance irrespective of dyslexia supports a dimensional view of this condition, and our results also suggest that it is the omega-3/omega-6 balance that is particularly relevant to dyslexia.

Omega-3 fatty acid status in attention-deficit/hyperactivity disorder

Lower levels of long-chain polyunsaturated fatty acids, particularly omega-3 fatty acids, in blood have repeatedly been associated with a variety of behavioral disorders including attention-deficit/hyperactivity disorder (ADHD). The exact nature of this relationship is not yet clear. We have studied children with ADHD who exhibited skin and thirst symptoms classically associated with essential fatty acid (EFA) deficiency, altered plasma and red blood cell fatty acid profiles, and dietary intake patterns that do not differ significantly from controls. This led us to focus on a potential metabolic insufficiency as the cause for the altered fatty acid phenotype. Here we review previous work and present new data expanding our observations into the young adult population. The frequency of thirst and skin symptoms was greater in newly diagnosed individuals with ADHD (n = 35) versus control individuals without behavioral problems (n = 112) drawn from the Purdue student population. A follow up case-control study with participants willing to provide a blood sample, a urine sample, a questionnaire about their general health, and dietary intake records was conducted with balancing based on gender, age, body mass index, smoking and ethnicity. A number of biochemical measures were analyzed including status markers for several nutrients and antioxidants, markers of oxidative stress, inflammation markers, and fatty acid profiles in the blood. The proportion of omega-3 fatty acids was found to be significantly lower in plasma phospholipids and erythrocytes in the ADHD group versus controls whereas saturated fatty acid proportions were higher. Intake of saturated fat was 30% higher in the ADHD group, but intake of all other nutrients was not different. Surprisingly, no evidence of elevated oxidative stress was found based on analysis of blood and urine samples. Indeed, serum ferritin, magnesium, and ascorbate concentrations were higher in the ADHD group, but iron, zinc, and vitamin B6 were not different. Our brief survey of biochemical and nutritional parameters did not give us any insight into the etiology of lower omega-3 fatty acids, but considering the consistency of the observation in multiple ADHD populations continued research in this field is encouraged.

Nutrition and theory of mind--The role of polyunsaturated fatty acids (PUFA) in the development of theory of mind

Breast-milk provides nutrients required for the development of the brain. n-6 and n-3 long-chain polyunsaturated fatty acids (LCPUFAs) have been suggested to be particularly involved. In this study levels of fatty acids in breast-milk were examined in relation to theory of mind (ToM) (n = 13) and WISC-III (n = 22) in six-year-old children. ToM tasks comprised four illustrated stories with questions about emotional (sad) events. Single polyunsaturated fatty acids (PUFA) were estimated as well as ratios between different fatty acids in order to describe putative associations between PUFA and psychological measures. Results show correlations between both ToM and WISC-III with single n-6 PUFA and the ratios DHA/AA and DHA/DPA. The correlations remained when socio-demographic factors were statistically controlled for. The positive findings related to the n-6 and n-3 LCPUFAs corroborate previous findings related to child cognitive development.

Time for an oil check: the role of essential omega-3 fatty acids in maternal and pediatric health

Deficiency of omega-3 fatty acids (omega3FAs) is an often unrecognized determinant of clinical disease; the adequate availability of these essential nutrients may prevent affliction or facilitate health restoration in some pregnant women and developing offspring. The human organism requires specific nutrients in order to carry out the molecular processes within cells and tissues and it is well established that omega3FAs are essential lipids necessary for various physiological functions. Accordingly, to achieve optimal health for patients, care givers should be familiar with clinical aspects of nutritional science, including the assessment of nutritional status and judicious use of nutrient supplementation. In view of the mounting evidence implicating omega3FA deficiency as a determinant of various maternal and pediatric afflictions, physicians should consider recommending purified fish oil supplementation during pregnancy and lactation. Furthermore, omega3FA supplementation may be indicated in selected pediatric situations to promote optimal health among children.

Omega-3 fatty acids in ADHD and related neurodevelopmental disorders

Omega-3 fatty acids are dietary essentials, and are critical to brain development and function. Increasing evidence suggests that a relative lack of omega-3 may contribute to many psychiatric and neurodevelopmental disorders. This review focuses on the possible role of omega-3 in attention-deficit/hyperactivity disorder (ADHD) and related childhood developmental disorders, evaluating the existing evidence from both research and clinical perspectives. Theory and experimental evidence support a role for omega-3 in ADHD, dyslexia, developmental coordination disorder (DCD) and autism. Results from controlled treatment trials are mixed, but the few studies in this area have involved different populations and treatment formulations. Dietary supplementation with fish oils (providing EPA and DHA) appears to alleviate ADHD-related symptoms in at least some children, and one study of DCD children also found benefits for academic achievement. Larger trials are now needed to confirm these findings, and to establish the specificity and durability of any treatment effects as well as optimal formulations and dosages. Omega-3 is not supported by current evidence as a primary treatment for ADHD or related conditions, but further research in this area is clearly warranted. Given their relative safety and general health benefits, omega-3 fatty acids offer a promising complementary approach to standard treatments.

Serum lipid fatty acids, phonological processing, and reading in children with oral clefts

Reading skill is suggested to be related to phonological processing ability and polyunsaturated fatty acids (PUFAs). Here we investigated whether fatty acids (FAs) are related to phonological processing, whether the relations between PUFAs and reading generalize to other FAs, whether these relations are mediated by phonological processing, and whether relations of FAs are specific for language-related functions. Blood samples of 49 ten-year-old children with oral clefts were collected for FA proportion analysis in serum cholesteryl esters and phospholipids. On the same day, they performed tasks of phonological processing, reading, and both verbal and nonverbal intelligence. Sequential regression analyses (adjusted for age, gender, and cleft type) showed that phonological processing was inversely related to myristic acid in phospholipids and positively related to eicosapentaenoic acid in cholesteryl esters. Reading was inversely related to palmitoleic and gammalinolenic acids in phospholipids. The relations between FAs and reading were not mediated by phonological processing and FAs related only to language-related functions.

Dietary fat intake is associated with psychosocial and cognitive functioning of school-aged children in the United States

Using cross-sectional data from the Third National Health and Nutrition Survey, 1988-1994, we examined whether dietary fat intake is associated with cognitive and psychosocial functioning in school-aged children. Based upon 24-h diet recall interviews, dietary intakes of total fat, SFA, monounsaturated fatty, PUFAs, and cholesterol were estimated in 3666 participants aged 6 to 16 y. Psychosocial functioning was evaluated in interviews of each child's mother. Cognitive functioning was measured using achievement and intelligence tests. Overall, total fat and saturated fat were unrelated to measures of cognitive and psychosocial functioning. Compared with equivalent energy intake from saturated fat or carbohydrate, each 5% increase in energy intake from PUFAs was associated with lower risks of poor performance on the digit span test (replacing SFA, OR = 0.58, 95% CI = 0.37-0.91; replacing carbohydrate, OR = 0.61, 95% CI = 0.43-0.88). Cholesterol intake was associated with an increased risk of poor performance on the digit span test (OR = 1.25, 95% CI = 1.11-1.42 for each 100-mg increment intake of cholesterol). The associations were independent of socioeconomic status, maternal education and marital status, and children's nutrition status and were consistent across different methods of energy adjustment in regression models. We conclude that high intake of PUFAs may contribute to an improved performance on the digit span test. In contrast, increased intake of cholesterol may be associated with a poorer performance.

Long-chain polyunsaturated fatty acids in childhood developmental and psychiatric disorders

Both omega-3 and omega-6 long-chain PUFA (LC-PUFA) are crucial to brain development and function, but omega-3 LC-PUFA in particular are often lacking in modern diets in developed countries. Increasing evidence, reviewed here, indicates that LC-PUFA deficiencies or imbalances are associated with childhood developmental and psychiatric disorders including ADHD, dyslexia, dyspraxia, and autistic spectrum disorders. These conditions show a high clinical overlap and run in the same families, as well as showing associations with various adult psychiatric disorders in which FA abnormalities are already implicated, such as depression, other mood disorders, and schizophrenia. Preliminary evidence from controlled trials also suggests that dietary supplementation with LC-PUFA might help in the management of these kinds of childhood behavioral and learning difficulties. Treatment with omega-3 FA appears most promising, but the few small studies published to date have involved different populations, study designs, treatments, and outcome measures. Large-scale studies are now needed to confirm the benefits reported. Further research is also required to assess the durability of such treatment effects, to determine optimal treatment compositions and dosages, and to develop reliable ways of identifying those individuals most likely to benefit from this kind of treatment. Childhood developmental and psychiatric disorders clearly reflect multifactorial influences, but the study of LC-PUFA and their metabolism could offer important new approaches to their early identification and management. Heterogeneity and comorbidity are such, however, that a focus on specific traits or symptoms may prove more fruitful than an exclusive reliance on current diagnostic categories.

EFA supplementation in children with inattention, hyperactivity, and other disruptive behaviors

This pilot study evaluated the effects of supplementation with PUFA on blood FA composition and behavior in children with Attention-Deficit/Hyperactivity Disorder (AD/HD)-like symptoms also reporting thirst and skin problems. Fifty children were randomized to treatment groups receiving either a PUFA supplement providing a daily dose of 480 mg DHA, 80 mg EPA, 40 mg arachidonic acid (AA), 96 mg GLA, and 24 mg alpha-tocopheryl acetate, or an olive oil placebo for 4 mon of double-blind parallel treatment. Supplementation with the PUFA led to a substantial increase in the proportions of EPA, DHA, and alpha-tocopherol in the plasma phospholipids and red blood cell (RBC) total lipids, but an increase was noted in the plasma phospholipid proportions of 18:3n-3 with olive oil as well. Significant improvements in multiple outcomes (as rated by parents) were noted in both groups, but a clear benefit from PUFA supplementation for all behaviors characteristic of AD/HD was not observed. For most outcomes, improvement of the PUFA group was consistently nominally better than that of the olive oil group; but the treatment difference was significant, by secondary intent-to-treat analysis, on only 2 out of 16 outcome measures: conduct problems rated by parents (-42.7 vs. -9.9%, n = 47, P = 0.05), and attention symptoms rated by teachers (-14.8 vs. +3.4%, n = 47, P = 0.03). PUFA supplementation led to a greater number of participants showing improvement in oppositional defiant behavior from a clinical to a nonclinical range compared with olive oil supplementation (8 out of 12 vs. 3 out of 11, n = 33, P = 0.02). Also, significant correlations were observed when comparing the magnitude of change between increasing proportions of EPA in the RBC and decreasing disruptive behavior as assessed by the Abbreviated Symptom Questionnaire (ASQ) for parents (r = -0.38, n = 31, P < 0.05), and for EPA and DHA in the RBC and the teachers' Disruptive Behavior Disorders (DBD) Rating Scale for Attention (r = -0.49, n = 24, P < 0.05). Interestingly, significant correlations were observed between the magnitude of increase in alpha-tocopherol concentrations in the RBC and a decrease in scores for all four subscales of the teachers' DBD (Hyperactivity, r = -0.45; Attention, r= -0.60; Conduct, r = -0.41; Oppositional/Defiant Disorder, r = -0.54; n = 24, P < 0.05) as well as the ASQ for teachers (r = -0.51, n = 24, P < 0.05). Thus, the results of this pilot study suggest the need for further research with both n-3 FA and vitamin E in children with behavioral disorders.

Clinical trials of fatty acid treatment in ADHD, dyslexia, dyspraxia and the autistic spectrum

Considerable clinical and experimental evidence now supports the idea that deficiencies or imbalances in certain highly unsaturated fatty acids may contribute to a range of common developmental disorders including ADHD, dyslexia, dyspraxia and autistic spectrum disorders (ASD). Definitive evidence of a causal contribution, however, can only come from intervention studies in the form of randomised, double-blind, placebo-controlled trials. Published studies of this kind are still fairly few in number, and mainly involve the diagnostic categories of ADHD and dyslexia, although other trials involving individuals with dyspraxia or ASD are in progress. The main findings to date from such studies are reviewed and evaluated here with the primary aim of guiding future research, although given that fatty acid supplementation for these conditions is already being adopted in many quarters, it is hoped that some of the information provided may also help to inform clinical practice.

Blood phospholipid fatty acid analysis of adults with and without attention deficit/hyperactivity disorder

Several psychiatric disorders, including juvenile Attention Deficit/Hyperactivity Disorder (ADHD), have been associated with abnormalities of certain long-chain PUFA (LCPUFA). Despite this reported association, the FA levels of patients with the adult form of ADHD have not previously been evaluated. In this study we measured the total blood phospholipid FA concentrations in 35 control subjects and 37 adults with ADHD symptoms to determine whether adults with ADHD symptoms would show abnormalities of FA relative to control subjects. In the serum phospholipids, adults with ADHD symptoms had significantly lower levels of total saturated, total polyunsaturated, and total omega-6 (n-6) FA, as well as the omega-3 (n-3) LCPUFA DHA (22:6n-3), and significantly higher levels of total monounsaturated FA and the n-3 LCPUFA docosapentaenoic acid (22:5n-3). In the erythrocyte membrane phospholipids, adults with ADHD symptoms had significantly lower levels of total PUFA, total n-3 FA, and DHA, and significantly higher levels of total saturated FA. Neither serum nor erythrocyte membrane phospholipid DHA was related to ADHD symptom severity (as assessed by the Amen questionnaire) in ADHD subjects. Although the exact cause of these variations is unknown, both environmental and genetic factors may be involved.

An explanation for the association between specific language impairment and toxemia

An association between specific language impairment (SLI) and toxemia has been detected in several studies. No clear explanation for this association has been identified to date. However, a number of potential explanations have been offered. These include: (1) toxemia causes fetal anoxia which leads to brain damage; (2) toxemia in the mother is an indication of maternal immune attack on the developing brain; (3) the association between toxemia and SLI is indirect and arises because both are consequences of a common but as yet unknown etiological factor. In this paper we present a fourth possible explanation for the association. That is, that both SLI and toxemia may be the consequence of low circulating levels of essential fatty acids. Evidence supporting this hypothesis is presented and four possible mechanisms underlying the association are discussed.

Visual motion sensitivity and reading

Reading is more difficult than speaking because an arbitrary set of visual symbols must be rapidly identified, ordered and translated into the sounds they represent. Many poor readers have particular problems with the rapid visual processing required for these tasks because they have a mild impairment of the visual magnocellular system. This deficit has been demonstrated using neuropathological, evoked potential, functional magnetic resonance imaging and psychophysical techniques. The sensitivity of the M-system in both good and bad readers correlates with their orthographic abilities, suggesting that the M-system plays an important part in their development. This role is probably to mediate steady direction of visual attention and eye fixations on words. Thus many children with reading difficulties have unsteady eye control and this causes the letters they are trying to read to appear to move around, so that they cannot tell what order they are meant to be in. Therefore, boosting M-performance using yellow filters, or training eye fixation, can improve reading performance very significantly. Several genetic linkage studies have associated reading difficulties with the MHC control region on the short arm of chromosome 6. This system has recently been shown to help regulate the differentiation of M-cells. This association could also explain the high incidence of autoimmune conditions in poor readers. Other chromosomal sites are associated with the metabolism of polyunsaturated fatty acids (PUFAs) as found in fish oils, and this could explain why PUFA supplements can improve reading.

The sensory basis of reading problems

Learning to read is much more difficult than learning to speak. Most children teach themselves to speak with little or no difficulty. Yet a few years later when they come to learn to read they have to be taught how to do it; they do not pick up reading by themselves. This is because we speak in words and syllables, but we write in phonemes. Syllables do not naturally break down into the sounds of letters and letter units (i.e., phonemes) because these do not correspond to physiologically distinct articulatory gestures (Liberman, Shankweiler, & Studdert-Kennedy, 1967). Alphabetic writing was only invented when people realized that syllables could be artificially divided into smaller acoustically distinguishable phonemes that could be represented by a small number of letters. But these distinctions are arbitrary cultural artifacts, and their mastery was originally confined to a select social class. And until about 100 years ago it did not matter much if the majority of people could not read; the acquisition of reading probably had no serious disadvantages. Reading requires the integration of at least two kinds of analysis (Castles & Coltheart, 1993; Ellis, 1984; Manis, Seidenberg, Doi, McBride-Chang, & Petersen, 1996; Morton, 1969; Seidenburg, 1993). First, the visual form of words, the shape of letters, their order in words, and common spelling patterns, which is termed their orthography, has to be processed visually. Their orthography yields the meaning of familiar words very rapidly without needing to sound them out. But for unfamiliar words, and all words are fairly unfamiliar to the beginning reader, the letters have to be translated into the speech sounds (i.e., phonemes) that they stand for, and then those sounds have to be melded together in inner speech to yield the word and its meaning. Reading exclusively by the phonological route is more time consuming than if words can be accessed directly without requiring phonological mediation.

Dyslexia and familial high blood pressure: an observational pilot study

BACKGROUND

Developmental dyslexia is a neurodevelopmental learning disability characterised by unexpectedly poor reading and unknown aetiology. One hypothesis proposes excessive platelet activating factor, a potent vasodilator, as a contributor, implying that there should be a negative association between dyslexia and high blood pressure (HBP). Since both conditions have a partial genetic basis, this association may be apparent at the familial level.

AIMS

To test this prediction in dyslexic and non-dyslexic children.

METHODS

Individuals and families with (HBP+) and without (HBP-) a family history of HBP were compared.

RESULTS

Proportionately fewer dyslexics (49/112) than controls (11/12) were HBP+. Families with multiple, all dyslexic children were less likely to be HBP+ (7/16) than those with a non-dyslexic child (11/11). Within families, mean child scores on reading were higher in the HBP+ group (mean 44.3, SE 0.95) than in the HBP- group (mean 40.3, SE 0.87).

CONCLUSION

HBP+ family history is associated with better performance on reading. The prediction of a negative association between dyslexic status and familial high blood pressure is therefore confirmed.

Could platelet activating factor play a role in developmental dyslexia?

Post-mortem studies by Galaburda and colleagues on the brains of developmental dyslexics found characteristic neuronal abnormalities: ectopias, microgyria, and fewer large-soma cells in sensory thalamus. An association between dyslexia and immune dysfunction has also been proposed. We describe a mechanism which may explain these observations. Platelet-activating factor (PAF) is a pro-inflammatory lipid implicated in neurological disorders. We propose that PAF may also be involved in dyslexia.

The magnocellular theory of developmental dyslexia

Low literacy is termed 'developmental dyslexia' when reading is significantly behind that expected from the intelligence quotient (IQ) in the presence of other symptoms--incoordination, left-right confusions, poor sequencing--that characterize it as a neurological syndrome. 5-10% of children, particularly boys, are found to be dyslexic. Reading requires the acquisition of good orthographic skills for recognising the visual form of words which allows one to access their meaning directly. It also requires the development of good phonological skills for sounding out unfamiliar words using knowledge of letter sound conversion rules. In the dyslexic brain, temporoparietal language areas on the two sides are symmetrical without the normal left-sided advantage. Also brain 'warts' (ectopias) are found, particularly clustered round the left temporoparietal language areas. The visual magnocellular system is responsible for timing visual events when reading. It therefore signals any visual motion that occurs if unintended movements lead to images moving off the fovea ('retinal slip'). These signals are then used to bring the eyes back on target. Thus, sensitivity to visual motion seems to help determine how well orthographic skill can develop in both good and bad readers. In dyslexics, the development of the visual magnocellular system is impaired: development of the magnocellular layers of the dyslexic lateral geniculate nucleus (LGN) is abnormal; their motion sensitivity is reduced; many dyslexics show unsteady binocular fixation; hence poor visual localization, particularly on the left side (left neglect). Dyslexics' binocular instability and visual perceptual instability, therefore, can cause the letters they are trying to read to appear to move around and cross over each other. Hence, blanking one eye (monocular occlusion) can improve reading. Thus, good magnocellular function is essential for high motion sensitivity and stable binocular fixation, hence proper development of orthographic skills. Many dyslexics also have auditory/phonological problems. Distinguishing letter sounds depends on picking up the changes in sound frequency and amplitude that characterize them. Thus, high frequency (FM) and amplitude modulation (AM) sensitivity helps the development of good phonological skill, and low sensitivity impedes the acquisition of these skills. Thus dyslexics' sensitivity to FM and AM is significantly lower than that of good readers and this explains their problems with phonology. The cerebellum is the head ganglion of magnocellular systems; it contributes to binocular fixation and to inner speech for sounding out words, and it is clearly defective in dyslexics. Thus, there is evidence that most reading problems have a fundamental sensorimotor cause. But why do magnocellular systems fail to develop properly? There is a clear genetic basis for impaired development of magnocells throughout the brain. The best understood linkage is to the region of the Major Histocompatibility Complex (MHC) Class 1 on the short arm of chromosome 6 which helps to control the production of antibodies. The development of magnocells may be impaired by autoantibodies affecting the developing brain. Magnocells also need high amounts of polyunsaturated fatty acids to preserve the membrane flexibility that permits the rapid conformational changes of channel proteins which underlie their transient sensitivity. But the genes that underlie magnocellular weakness would not be so common unless there were compensating advantages to dyslexia. In developmental dyslexics there may be heightened development of parvocellular systems that underlie their holistic, artistic, 'seeing the whole picture' and entrepreneurial talents.

Fatty acid metabolism in neurodevelopmental disorder: a new perspective on associations between attention-deficit/hyperactivity disorder, dyslexia, dyspraxia and the autistic spectrum

There is increasing evidence that abnormalities of fatty acid and membrane phospholipid metabolism play a part in a wide range of neurodevelopmental and psychiatric disorders. This proposal is discussed here in relation to attention-deficit/hyperactivity disorder (ADHD), dyslexia, developmental coordination disorder (dyspraxia) and the autistic spectrum. These are among the most common neurodevelopmental disorders of childhood, with significant implications for society as well as for those directly affected. However, controversy still surrounds both the identification and management of these conditions, and while their aetiology is recognized as being complex and multifactorial, little progress has yet been made in elucidating predisposing factors at the biological level. An overview is provided here of the contents of this Special Issue, which contains a selection of reports from a unique multidisciplinary workshop involving both researchers and clinicians. Its purpose was to explore the possibility that ADHD, dyslexia, dyspraxia and autism fall within a phospholipid spectrum of disorders. This proposal could explain the high degree of co-morbidity between these conditions, their aggregation within families and relation to other psychiatric disorders, and a range of associated features that are already well known at a clinical level. The existing evidence for fatty acid abnormalities in these disorders is summarized, and new approaches are outlined that have the potential to improve both the identification and the management of these and related neurodevelopmental and psychiatric conditions.